ArcGis workflows

From website:https://courseware.e-education.psu.edu/courses/geog484/L03_compiled.html

(Goes from lesson 1 thru 6)

Lesson 3: Georeferencing Raster Images

Scenario: Registering an Image for the Purpose of Data Creation

Introduction

A. Goals

Upon completion of this project, you will be able to georeference a raster image for the purposes of heads-up digitizing, or for the sake of adding visual information to accompany existing GIS data.

B. Background

We have been using spatial vector data provided by vendors, we have been creating our own vector data, and in Lesson 5 we will be downloading data from the Web. Effective use of the analytical and display capabilities of GIS software often requires that all layers pertinent to a given area of interest be in registration--be in the same georeferenced coordinate system. In Geography 482 you learned that such coordinate systems can be either spherical or Cartesian. Spatial data representing mapped, or flattened, portions of the world are stored in 2-dimensional Cartesian coordinates based on a map projection. In contrast are spherical coordinates, represented by degrees of longitude and latitude (often referred to, for the sake of convenience, as the "geographic" projection, though it is not a map projection, per se). You may want to review some of the material in Lesson 2 of Geography 482.

Viable GIS datasets compiled from different sources may be in different georeferenced coordinates -- for example, UTM or State Plane or Albers Equal Area Conic or Lambert Azimuthal Equal Area. (Remember that UTM and State Plane are technically referred to as "coordinate grid systems," not map projections, because in both cases the measured Cartesian grid has an origin other than at the origin of the map projection on

which they are based.) A robust GIS has tools that allow you to change from one coordinate system or map projection to another. In other words, it has tools that enable you to re-project the already georeferenced data.

This lesson is not about changing map projections, however. We will visit that process in Lesson 5 and again in the Final Project.

When the source of new data for use in the GIS is a tablet digitizer or a scanner, there is an arbitrary Cartesian coordinate system imposed on the new dataset by the digitizing method [XY coordinates in inches from the tablet digitizer, or cells (or pixels) per inch from the scanner]. The process of converting from the digitizing method-imposed coordinates to georeferenced coordinates is known as georeferencing. In general, converting from any referencing system to coordinates that define a location on the surface of the Earth is referred to as georeferencing. For example, converting from postal addresses to longitude-latitude coordinates (address-matching) is a type of georeferencing.

The process that we refer to as georeferencing actually comes about via one of four transformation methods. In this lesson you will apply two different transformation methods to three different datasets, via two software techniques:

1. Using an affine transformation, and explicit XY coordinates of control points, you will georeference a USGS DRG that has "lost" its georeferencing information.

2. Using an affine transformation and, again, explicit XY coordinates of control points, you will georeference a scanned portion of a paper version of the same USGS topo quad represented by the DRG referred to in #1 above.

3. Using a second-order polynomial transformation, you will attempt to georeference a vertical aerial photograph (not orthorectified) by using an interactive tool to specify pairs of control points.

Learn more about coordinate transformation and georeferencing in the Concept Gallery.

The transformation methods are usually best-fit using a statistical method that seeks to minimize what is called the root mean square error, RMSE, or RMS error. The RMS error provides a comparison of the measured and predicted control points. Which gives us an indication of the quality of the transformation.

Learn more about RMS error in the Concept Gallery.

C. Overview

1. Georeference a USGS DRG.

2. Georeference a scanned USGS paper topographic quadrangle.

3. Georeference a vertical aerial photo that has not been orthorectified.

D. Lesson Data Preparation

The data you need for Lesson 3 are available here for download.

Lesson3.zip

This single zip file is ~14 MB and will take approximately 33 minutes to download over a 56 Kbps modem.

If you are, in deed, connecting via a modem I have broken the Lesson 3 data up into 4 .zip files. Instead of attempting to download the single Lesson3.zip file you could download these four.

Lesson3_1.zip 23 KB, it'll take 3 seconds

Lesson3_2.zip ~2.6 MB, approximately 6 minutes via modem

Lesson3_3.zip ~3.2 MB, approximately 7.5 minutes via modem

Lesson3_4.zip ~8.1 MB, approximately 19 minutes via modem (I'm sorry, I cannot make it smaller.)

Once you have downloaded the .zip file(s), extract the archived files. If you use the extract feature of your compression software and be certain that you extract the Lesson3 folder along with its contents. Else you can create a Lesson3 folder in your \WCGIS\GEOG484 directory path and drag-and-drop the individual files out of your compression utility into it.

Your Lesson3 folder, when viewed via Windows Explorer or a My Computer window, should contain 11 files:

DRG_utmControlPoints.txt

map_utmControlPoints.txt

statecollege_DRG.tif

statecollege_map.tif

statecollege1963.jpg

StCol_Rds.dbf

StCol_Rds.prj

StCol_Rds.sbn

StCol_Rds.sbx

StCol_Rds.shp

StCol_Rds.shx

The files are now ready to use in this lesson. The two .txt files contain information duplicated in the lesson write-up. I provide these text files to give you the option to copy-and-paste versus key-stroke entering of information. The two .tif files and the .jpg files are images that you will georeference in the course of the lesson. The remaining 6 files, all having the same StCol_Rds root name, comprise a shapefile dataset, named, you guessed it, StCol_Rds.

E. Deliverables

These deliverables are due two weeks after the Lesson is revealed. See the course Calendar for the specific due date.

1. A single Microsoft Word document should be submitted, containing all of the deliverables for this Lesson. (If you use WordPerfect please save as a .doc file before you submit. Please do not send a WordPerfect document. Please DO NOT submit a PowerPoint document.)

Incorporate your name into the name of your document file: something similar to "JSloan_Lesson3.doc" (your first initial and your last name).

Upload your document file to the Lesson 3 Drop Box - Don't forget to hit the Submit button!

Your document should contain the following, in the order specified:

a. Screen captures of the three data frames, taken where specified in the lesson write-up.

Each screen capture should show:

the ArcMap interface Table of Contents, so we can determine the activated layer.

the entire Link Table, so we can see the list of links and the Transformation method and RMS error.

the coordinate readout slot, at the bottom of the ArcMap interface window.

Your screen capture images need to be clear and comprehensible. Please do not include your desktop background as part of the image(s). (If you use the Print Screen button to capture the screen image, know that by holding down the Alt-key when hitting the Print Screen button you will be able to capture only the active window. This can help make your screen captures more space-efficient.) Switching the page format of your Word document to landscape orientation will allow for placement of wider images. The image file formats most often used include .png, .jpg, .gif, .bmp or .tif. Lastly, be sure to review your document in either a print layout view or the print preview (change zoom to 75%) before uploading and submitting.

b. Show how you calculated the threshold value of "an acceptable RMS error" that was called for in Part II Section B Step 7.

c. Based on the discussion in the Concept Gallery, and on the comments in the Lesson write-up, answer the following questions. The explanations asked for are important--we want to be certain you understand the concepts. Be succinct.

Does the RMS error that you ended up with for the statecollege_DRG.tif have any diagnostic value? Explain your answer. If it does, do you consider it acceptable? Explain why.

Does the RMS error that you ended up with for the statecollege_map.tif have any diagnostic value? Explain your answer. If it does, do you consider it acceptable? Explain why.

Does the RMS error that you ended up with for the vertical air photo of State College have any diagnostic value? Explain your answer. If it does, do you consider it acceptable? Explain why.

d. List a minimum of 5 factors that might limit your ability to arrive at a low RMS error when georeferencing raster image data.

2. Make an entry in your e-Portfolio, reflecting upon the Lesson. (Do NOT post any of the specific results of the Lesson homework to your e-Portfolio web site.)

3. Take the Lesson 3 quiz.

Lesson 3: Georeferencing Raster Images

Scenario: Georeferencing an Image for the Purpose of Data Creation

Part I: Getting Started

A. Organize the data - Create three map documents

In this section you will set up 3 map documents.

1. Open ArcCatalog.

2. Create a connection to your Lesson3 directory. Note the contents of the Lesson3 folder: 2 text files, 3 image files and 1 shapefile dataset.

Let's create the first map document .

3. Open a new map document in ArcMap.

4. Use the Add Data button (the Plus-sign tool on the Standard toolbar) to bring the statecollege_DRG.tif image into your map document.

5. In the Create Pyramids for... box that appears, select Yes. This process may take several seconds, but creation of the pyramids file will increase the subsequent rendering speed of the image.

6. Click OK to the "...missing spatial reference information...." message. It should not be a surprise that we received this message. After all, the point of the exercise is to georeference the image file.

It is possible that the image will display as either solid black, or in shades of gray. Please let me know if this happens to you. It should be in color, looking like a typical USGS topographic quadrangle map. If your image appears black or in gray-scale, right-click on it in the Table of Contents pane and Remove it. Then Add it again. It should now be alright. If it initially came in as a solid black you may have to Remove it and add it a second time. This behavior is new with version 9.x of the software. I have yet to track down an explanation. With past versions of the software the .tif images came in to the ArcMap session in color, as expected. The

rendering in grays or in black seems to only happen with TIFF image files, not with JPEG images for example. Going into the ArcCatalog interface before attempting to add the image files to an ArcMap session, right-clicking on each image file, and choosing to both Calculate Statistics and Build Pyramids (accepting all default settings) is a more proactive way of preventing the black/gray-scale symbolization from happening, but I have no explanation yet as to why.This may happen with the second TIFF image you add, below, too.

7. Change the name of the data frame from the default Layers to State College DRG by right-clicking on Layers and selecting Properties. The Name is found under the General tab. (Or, simply left-click, on the Layers name, pause, then left-click on it again. The Layers name should be highlighted and you can then type over it.)

If, via Windows Explorer or a My Computer window, you look in your Lesson3 folder you will now see a statecollege_DRG.rrd file and a statecollege_DRG.aux file. You may need to View | Refresh. (The .rrd file may initially show a name similar to : ...DRG_1192214622.rrd.) These were just created. The .rrd file is the pyramids file. The file extension letters stand for reduced resolution dataset. The file is actually a lower-resolution copy of the original image. The .aux file is an auxiliary file that is associated with raster datasets. You were briefly introduced to the auxiliary file in Lesson 2. Again, to learn more about it, open the ArcGIS Desktop Help and Search on aux. Look at the About auxiliary (AUX) files topic.

The statecollege_DRG.tif file is a USGS DRG that I have made "lose" its georeferencing information. (A USGS DRG is, by definition, in the Geotif format; a TIFF image with georeferencing information built into it.) You will georeference it, based on the UTM (meters) coordinates of the corners of the map. Because the image is derived from a DRG it is free of distortion, and so you should be able to do an accurate job of georeferencing.

Let's do a few more things:

8. Right-click on the name of the image file on the Table of Contents pane, and select Properties.

9. In the Layer Properties window that opens, click the Source tab. Scroll down through the information, taking note of the Cellsize, the Extent values, and the fact that the Spatial Reference information is undefined.

Given that the map image that we are dealing with is a reproduction of a USGS 1:24,000 scale topographic map, we can surmise that the Extent

values are in units of inches. A paper version of this map would be approximately 20.6 inches wide and 27.4 inches high. Given that the units are in inches, the Cellsize of .004 equates to 1/250th of an inch. Or in other words, the resolution of the image file is 250 cells per linear inch.

10. Click the Cancel button to close the Layer Properties window.

11. Now, right-click in the data frame/map display area and select Data Frame Properties (In v.9.1 the choice is Properties.) to bring up the Data Frame Properties window. Click the General tab and change the Units, Map: and the Display: units to Inches. This way you get the proper, more easy to read values in the coordinate read-out slot at the bottom-right of the ArcMap interface.

12. Next, while you are still in the Data Frame Properties window, click the Frame tab. In the Background area of the dialog, go to the dropdown arrow and chose a color other than white. Then click OK to close the Data Frame Properties window. You can now see the true extent of the image file. Put your mouse cursor in the lower-left corner of the white map collar. This is where the 0,0 origin of the image file coordinate system is.

13. Activate the Georeferencing toolbar (View | Toolbars | Georeferencing).

14. Go to the File menu and Save the map document to your Lesson3 folder. Name it DRG_<your first initial and your last name>. For example, DRG_JSloan.

Next we will create a second map document .

15. From the File menu choose New, and with the lower-left radio button for Document selected, click OK. Or click the New Map File icon on the Standard tool bar (the white page icon).

16. Change the name of the data frame from the default Layers to Map State College.

17. To the data frame, add the statecollege_map.tif image.

18. Build the pyramids, and click OK to the "...missing spatial reference information...." message. This image should be in color. If it is not, attempt the steps that I outlined above in the Step 6 Note. The statecollege_map.tif file is a scan of a portion of a USGS paper topo sheet. You will georeference it, based on the UTM (meters) coordinates of four tick marks found on the map.

The statecollege_map.tif image file has no georeferenced--or real-world--spatial reference information associated with it either. But, chances are, you did not receive the "...missing spatial reference information..." message after you built the pyramids. If we were to have closed ArcMap, then reopened it before adding the image file of the map we would have received the "...missing spatial reference information..." message. What's more, if we were to have added the image file to the new map document that we had created from the already-open ArcMap session, via the drag-and-drop method from ArcCatalog, we may have actually received the "...missing spatial reference information..." message. I find disconcerting the fact that you do not always get the"...missing spatial reference information..." message. The lesson we should take away from this is to investigate the Properties of a dataset via ArcCatalog in order to directly learn what we can about the data we are working with.

19. If you bring up the Layer Properties of the statecollege_map.tif image you will see that the resolution of this image file is also 250 cells per linear inch (.004 inches on a cell side): It is a scan of only the lower right portion of the paper quadrangle map, so its dimensions are approximately 8.5 by 14 inches; the cell size is .004 by .004 (inches).

20. Go ahead and change the Map: and Display: units to Inches for this data frame, too. If you desire, change the background color of the data frame as well.

21. Activate the Georeferencing toolbar.

22. Save the map document and name it Map_<your first initial and your last name>. For example, Map_JSloan.

Next we will create the third map document.

23. Create a third map document -- you know how to do it.

24. Change the name of the data frame from the default Layers to State College 1963 Photo.

25. Add first and separately the statecollege1963.jpg image into the State College 1963 Photo data frame. This is a black-and-white image.

26. Build the pyramids. Again, even though this image file has no real-world spatial information associated with it, dependng upon how you created the new map document, you may not see the "...missing spatial reference information...." message.

27. Now, Add the StCol_Rds.shp layer to this data frame. Even though it shows in the Table of Contents pane, it will not appear in the map display area; its

coordinates do not match those of the photo, so they do not appear together....yet. Leave the data frame in this state.

28. Do not alter the Map: or Display: units this time.

The statecollege1963.jpg file is a scanned image of a vertical aerial photo. It is NOT orthorectified. This implies that the horizontal scale varies throughout the photo, and that the photo is not projected into any sort of Cartesian coordinate system. You will still attempt to georeference it, based on creating transformation links between road intersection locations.

29. Activate the Georeferencing toolbar.

30. Save the map document and name it Photo1963_<your first initial and your last name>. For example, Photo1963_JSloan.

That is it for Part I

You have just completed Part I of this activity, which involved preparing three image files (in three separate map documents) for georeferencing. In Parts II and III, you will register the images to georeferenced, or real-world, coordinates.

Lesson 3: Georeferencing Raster Images

Scenario: Georeferencing an Image for the Purpose of Data Creation

Part II: Georeferencing Using Explicit XY Coordinates of Control Points

In this Part of the project you will be working with the two TIFF images that you added, respectively, to the first two data frames that you created in Part I. The first is a DRG (Digital Raster Graphic) of the State College 1:24,000 USGS topographic quadrangle that no longer has georeferencing information associated with it. (Recall that a USGS DRG, by definition, is a Geotif, and therefore is georeferenced. For the sake of the lesson I have destroyed the georeferencing information.) The second image is a scan of the lower-right portion of a paper version of the same State College topographic quadrangle. (Although it is an older version than the DRG.) Be certain to examine the characteristics of the paper map that can be viewed in the image. Note the fold near the top.

Control points, or transformation links, come in pairs: an x-y coordinate location corresponding to a point on the un-georeferenced layer and an x-y coordinate for the same location in the georeferenced, or real-world, coordinate system that you are transforming the coordinates of the un-georeferenced layer to. In both of the cases

dealt with in this Part of the Lesson, you will be establishing the values of the control points on the digitized (un-georeferenced) layer by interactively clicking on specific locations on the image of the topo map. You will then explicitly add the coordinate values for the georeferenced counterparts of those same locations by typing in (or copy-and-pasting) the UTM (meters) coordinate values.

(For those of you who realize that the topographic quadrangle maps used in Part II of this lesson are actually cast on a polyconic map projection, and not on the UTM system, I offer the following excerpts from Paul Bolstad, GIS Fundamentals, 2002, Eider Press: "...USGS 1:24,000-scale maps are cast on a polyconic projection. If these maps are digitized, it would be preferable to register them to the appropriate polyconic projection, and then re-project these data to the desired end projection. This is often not done, because the error in ignoring the projection over the size of the mapped area is typically less than the positional error associated with digitizing. Experience and specific calculations have shown that the spatial errors in using a transformation instead of a projection are small at these map scales under typical digitizing conditions." So, technically we are transforming between map projections, something that should normally be avoided. Again, from Bolstad: "...USGS 1:24,000 maps are often digitized directly into a UTM coordinate system with no obvious ill effects, because the errors in map production and digitizing are often much larger than those in the projection distortion for the map area. However, you should not infer this practice is appropriate under all conditions, particularly when working with smaller-scale maps." So, for the sake of the lesson and the questions you are to answer in part (c) of the Deliverables, consider our use of transformation techniques to georeference the State College topo maps to be valid.)

Regarding the management of your time relative to this lesson: You should plan to go through Sections II-A and II-B with out stopping. And once you begin Section II-C do not stop until you get through Section II-D. Then, without stopping, do all of Part III. You can do these three phases separately, just do not stop within them. If you find it necessary to do so, then I advise that you start over with the georeferencing of the image involved. There are guidelines for starting over in the Note at the end of Step II-B-12.

A. Create temporary transformation links

In Step II-B-7 you are asked to perform a calculation. I recommend that you read through the lesson to that point, then attempt that calculation before beginning Section II-A of the step-by-step instructions. That way you will be able to proceed from Step II-B-7 to Step II-B-8 without interruption.

1. Open the DRG_<your name> map document.

2. Before proceeding let's do a little bookkeeping. We are going to set the coordinate system of the data frame. Based on the discussion in the introduction to this section and on the information that can be seen in the lower-left portion of the map collar we are going to be georeferencing the

image file to the UTM Zone 18 NAD27 coordinate system. By explicitly defining the coordinate system of the data frame the name of the coordinate system will be automatically associated with the georeferenced image file once we complete the georferencing steps.

a. Right-click in the map display area/data frame and bring up the Data Frame Properties dialog window.

b. Click on the Coordinate System tab. In the lower pane of properties window you will see that the coordinate system of the data frame is currently Unknown.

c. Expand the Predefined list through Projected Coordinate Systems, then UTM, then Nad 1927, then...

d. select (click to highlight) NAD 1927 UTM Zone 18N

e. Click the OK button. (You may need to use the Full Extent tool to bring the map back into view.)

3. Notice that the label in the coordinate readout slot now reads Meters. The units of the UTM coordinate system are meters.

4. Verify that the statecollege_DRG.tif file name appears in the Layer: window of the Georeferencing toolbar. (It should be, it is the only layer in that data frame!)

5. On the Georeferencing toolbar, click on the View Link Table button . The Link Table will open.

6. In the lower-left of the Link Table note the check box labeled Auto Adjust. We are going to leave it checked. As a result you will witness slight alterations/movements in the image as you go through the next 5 steps. (The Auto Adjust setting is also located under the Georeferencing pulldown menu.)

7. Move the Link Table so it is not obscuring the map display area.

8. Zoom in on the upper-left corner of the map neat line, labeled "1" in red. (The neatline is the black/brown border of pixels that bounds the map.) Attempt to zoom in until you can clearly see the cell resolution of the image file, but not so far in that you loose track of where you are in the context of the image. See Figure 1.

9. Select the Add Control Points tool by clicking on it.

10. Establish the first image-based control point (the "From" control point) by clicking on the upper-left corner of the map neat line. Then, for the time being, establish the georeferenced control point (the "To" control point) by clicking anywhere, a short distance away. [See Figure 1.] An entry will appear in the Link Table. You have created the first transformation link.

In Step11 you will be instructed to create 3 more links at the remaining corners of the map. You can toggle among the Full Extent tool, the Zoom In tool and the Add Control Points tool in order to create the remaining three links. It does not matter where you initially specify the "To" or georeferenced control point location (the second left-click defining each control point pair), since you will be explicitly specifying these coordinates in a later step.

When interactively establishing control point locations that define transformation links, you always establish the control point on the un-georeferenced layer first, then define the control point on the georeferenced, or target layer. The TIFF image of the DRG is what we have set out to georeference, so we establish the first control point of each link in reference to it.

11. Now, add links for the other three control points in the same manner. They are located at the other three corners of the map, and should be added in the order that they are numbered (see the large, red numerals adjacent each corner of the map).

If you look at the Link Table after you add each link you will see that the values in the Residual column, and the value for the Total RMS Error will be blank or 0, until you add the fourth link. Recall from the Concept Gallery that, even though the Affine transformation can be performed based on 3 control point pairs (links), it requires at least 4 control point pairs for the RMS Error to be calculated. In our case, at this point, even though there are now four control point pairs in the Link Table the residuals and the RMS error are meaningless because you have yet to define the "To" points in georeferenced coordinates--the UTM values of the map projection.)If you had un-checked the Auto Adjust box before beginning the creation of the control points, the RMS error and the residual values would not show at all, until you reactivated the AutoAdjust.

B. Update the "To" coordinates of the transformation links in the Link Table

map corner X_coord Y_coord name

UL 257730.594 4528648.872 Upper-Left

UR 268265.246 4528310.190 Upper-Right

LR 267829.563 4514432.325 Lower-Right

LL 257275.067 4514770.789 Lower-Left

Table 1. Georeferenced (real-world) values for DRG control points (UTM Zone 18, NAD27). (The longitude-latitude coordinates that define the corners of the topo quad can be converted to UTM Zone 18 NAD27 meters values using tools such as that found on the Web at http://www.ngs.noaa.gov/cgi-bin/utm_getut.prl.)

1. Retrieve the Link Table if it is hidden. It should list 4 control point link pairs.

2. In the Lesson3 folder, find and open the DRG_utmControlPoints.txt file. (If the columns and column headings do not line up, change the font to Arial.) You are going to replace the values in the X Map and Y Map columns of the Link Table with the values from the Xcoord and Ycoord columns from the text file. The same values are found in the Table 1, above.

3. In the Link Table, uncheck the Auto Adjust box, found in the lower-left.

4. Now, in turn, highlight each value in the X Map and Y Map columns in the Link Table, and replace it with the corresponding Xcoord and Ycoord value from the DRG_utmControlPoints.txt file. You have to click once to highlight the row, in the Link Table, then click on the X or Y value to highlight it. You can avoid errors if you copy-and-paste from the text file into the Link Table. Note the values for the Residuals in the Link Table. They will change to something more meaningful in the next step.

A more realistic scenario, perhaps, would have the control point links being established at road intersections, for example. The georeferenced coordinates of the control point locations coming from surveyed or GPS measurements.

5. Had we left the Auto Adjust active, the map image would have drastically distorted as you supplied the X Map and Y Map values. As fun as this might be to witness, it also tends to slow down your computer as it processes each alteration of the display caused by the modification of the control point pairs.

After you have finished entering the georeferenced (UTM) coordinate values, re-activate the Auto Adjust. The map display area will probably go

blank. You will need to reset the extent of the data frame. Right-click on the statecollege_DRG.tif layer in the Table of Contents and select Zoom to Layer. Or, just click on the Full Extent tool.

6. If you run the cursor over the map display area, you should notice that the coordinates in the lower right of the window are now much larger values that they were before you began the georeferencing process. The values are now reflecting the fact that you are transforming the image file into UTM coordinate space.

7. Turn your attention back to the Link Table.

Now, since supplying the UTM coordinate values for the "To" control points, the Total RMS Error value in the lower-right of the Link Table means something--it is diagnostic of the quality of the placing of the control point links, diagnostic of the georeferencing process--for two reasons: (1) you have replaced the temporary values of the "To" control points with the correct and appropriate georeferenced coordinate values, and (2) there are four valid pairs of control points--four transformation links. By "appropriate" in #1 of the previous sentence I mean that the coordinates of the "To" control points are in the same coordinate system as that of the map that was scanned. Alluded to in #2 above is the fact that you need 4 control point pairs in order for the RMS error to be calculated.

A rule-of-thumb for what is an acceptable RMS error when georeferencing a raster image is... what? Do you recall from the Concept Gallery? Given that this is an original USGS DRG file and therefore has a cell (pixel) resolution of 250 cells/inch, and that the scale of the original scanned topo sheet is 1:24,000, can you determine how many meters on the ground the side of one cell represents (since we are working in UTM meters)? Then, based on the rule-of-thumb referred to above can you arrive at what is a reasonable/acceptable RMS error for this exercise? I hope so.

I want you all to grapple with this on your own, without any help from me or from each other via the message board. When you feel you have grappled enough and want verification of, or help with, your calculations, contact me (Jim Sloan) via the Course e-mail system. (Do not spend an inordinate amount of time on this. I just want you to take a good stab at it.)

Also, be certain to supply your complete calculation in the deliverables for this lesson.

8. If you have an inordinately high RMS error you can do one of two things: Based on the values in the Residual column you can highlight and delete, from within the Link Table, individual links having high residual values. (The stylized X button at the upper-right of the table is the Delete button. The center of the cross hair of the selected control point turns from blue to

yellow.) Or you can Delete Control Points from the Georeferencing dropdown menu. This will delete all links. You will need to update the data frame with the Full Extent tool in order to bring the image back into view. If you replace any links, be certain to copy and paste the correct values for the "To" coordinates from the text file.

Making a mistake while typing or copying-and-pasting the XMap and YMap values will result in a high RMS error.

9. At this point, if you are satisfied with your RMS error, hit the Save button that is in the Link Table window. You will be saving the coordinates of the control point links in a text file. Give the file an appropriate name and save it in your Lesson 3 folder. This is not always necessary, but is not a bad idea. (If you want to view the contents of the text file, it is better rendered with WordPad than it is with NotePad.) DO NOT close the Link Table.In the following step you are asked to make the first of three screen captures that are to be part of your Deliverables for the Lesson. The Link Table would NOT be retained by simply saving the ArcMap session; if you finish the lesson and close ArcMap before you make your screen capture you will not be able to retrieve the Link Table. Having saved the Link Table contents to a .txt file gives you something to fall back on, just in case.

10. Make your screen capture. This is a required part of your deliverables. See Figure 2. for what I expect to see in your screen captures.

11. Now, go to the Georeferencing dropdown menu and select Update Georeferencing. This is a crucial step.

This Note pertains to the results if you are using version 9.2. If you are using version 9.0/9.1, take a look at the next Note. In Windows Explorer, or My Computer, look in your Lesson3 folder. You may need to View | Refresh. If you have installed Service Pack 2 or 3 or 4 for version 9.2 you will see two new files. One named statecollege_DRG.tif.aux.xml and one named statecollege_DRG.tfwx. If you have not yet installed Service Pack 2 the only new file will be the statecollege_DRG.tif.aux.xml. (One of the reasons for Lesson 0!) The file with the .tfwx extension is the world file. Open the world file with WordPad. This world file contains information crucial to the georeferencing of the statecollege_DRG.tif file. As long as the image file and the world file are kept together in the same directory the image will be interpreted by the GIS program as being georeferenced. The GIS software, however, will not know WHAT the georeferenced coordinate system is--look again in the world file, there is no information in it stating that the coordinate system is UTM NAD1927 Zone 18. The .xml file contains the georeferencing information, too, but it also contains

the name of the coordinate system. This is by virtue of our having set the coordinate system of the data frame before we began the georeferencing process. So, if the original image file and either the .xml file or the .tfwx file are kept together, in the same folder, the GIS will be able to properly display the image file in the georeferenced coordinate system. The .xml file is more complete in that it can store the name of the coordinate system, but the contents of the world file (the .tfwx file) are accessible via a text editor, which can come in handy if you perceive of a need to alter any of the parameters that it contains. The scope of this course does not allow us to explore the need to do so. The world file is also often necessary when the image file is intended for use in software other than ArcGIS. (If you have not complied with Lesson 1 and have not installed Service Pack 4 (or at least SP2) for version 9.2 all is not lost (except maybe my patience with you! -- kidding), because, as is explained above, all of the necessary information required for your georeferencing efforts to be viable is contained in the statecollege_drg.tif.aux.xml file. As long as the image file and the .xml file are kept together in the same directory the image will be interpreted by the GIS program as being georeferenced, and the GIS will know WHAT the georeferenced coordinate system is. A last note, regarding the .aux file. Prior to version 9.2 the .aux file used to serve a purpose similar to that of the .xml file. (See the Note below.) This no longer is the case in version 9.2. The .aux file does not get updated with the name of the coordinate system as it does in versions 9.0/9.1.

If you are using version 9.0/9.1 things are a bit different: In Windows Explorer, or My Computer, look in your Lesson3 folder. You may need to View | Refresh. You should find one new file, called statecollege_drg.tfw. You should also notice that the time stamp on your statecollege_drg.aux file has been updated.(Recall that the .aux file was actually first created when you Added the image to your ArcMap session.) The .tfw file is called a world file. Its extension is automatically formed by taking the first and last letters of the .tif extension, then adding a "w". The world file contains the 6 coefficients for the two equations created during the affine transformation. (Recall the information in the Help files, referred to in the Concept Gallery.) Open the world file with WordPad. This world file contains the information crucial to the georeferencing of the statecollege_drg.tif file. As long as the image file and the world file are kept together in the same directory the image will be interpreted by the GIS program as being georeferenced. The GIS software, however, will not know WHAT the georeferenced coordinate system is--look again in the world file, there is no information in it stating that the coordinate system is UTM NAD1927 Zone 18. The .aux, or auxiliary, file contains the georeferencing information, too, but it also

contains the name of the coordinate system, if it has been supplied. So, if the original image file and either the .aux file or the .tfw file are kept together, in the same folder, the GIS will be able to properly display the image file in the georeferenced coordinate system. The .aux file is more complete in that it can store the name of the coordinate system, but the contents of the world file (the .tfw file) are accessible via a text editor, which can come in handy if you perceive of a need to alter any of the parameters that it contains. The scope of this course does not allow us to explore the need to do so. The world file is also often necessary when the image file is intended for use in software other than ArcGIS.

One last point: If you want to re-georeference an image file, it is necessary to delete the world file, the .aux file and the .xml file (if using v.9.2), and to set up a new map document before doing so.

12. Before we move on let's check the Properties of the image file again. Right-click on the name of the statecollege_DRG.tif image file on the Table of Contents pane, and select Properties.

13. In the Layer Properties window that opens, click the Source tab. Scroll down through the information, comparing the Cellsize, the Extent values, and the Spatial Reference information to what you recall from doing so in Step A-9 of Part I.

Instead of .004 the Cellsize is now 2.438 (if you did a good job of positioning the "From" control points). What are the units? The Extent values reflect the fact that the coordinates are now in terms of the UTM system. The Spatial Reference information is now present.

14. Cancel out of the Properties window.

15. Save the map document.

This exercise served, hopefully, to give you a feel for what it is like to georeference an image file where you can expect the RMS error to be low. The image file, one I derived from a USGS DRG, was, for all intents and purposes, distortion-free. And the coordinate values for the georeferenced control points you entered explicitly, rather that interactively (as you will do in Part III). So, the primary source of error that would contribute to an unsatisfactory RMS error was your use of the Add Control Points tool to place the un-georeferenced ("From") control points--on the image. If you were careful, and patient, you should have come up with an RMS error within an acceptable range. Keep all this in mind and compare it to the situation in the next portion of the lesson.

C. Georeference the scanned image of a paper map

The TIFF image that you will work with in this section was created by scanning, on a flatbed scanner, a portion of an older paper version of the same USGS topographic quadrangle that you dealt with above. So, the scale of the original paper map is 1:24,000. And, as with the DRG-based image in the previous Section, the cell (pixel) resolution of this scanned image is 250 cells/inch. You will be executing the same basic steps as you did above in order to georeference it, but you will have the option to use an alternative way of supplying the "To" control points values (note Steps 7 and 8, below), and, in Section D, you will learn the second way to assign the coordinate system definition to an image file.

map loc X_coord Y_coord name

UL 264458.724 4519169.425 Cross-hair

UR 267974.667 4519058.254 47'30" side

LR 267829.563 4514432.325 LR Corner

LL 264311.416 4514543.472 47'30" bottom

Table 2. Georeferenced values for the statecollege_map.tif control points (UTM Zone 18, NAD27).

1. Open the Map_<your name> map document..

2. Familiarize yourself with the image, particularly the fold near the top. Find the four labeled (in black numerals this time) locations that define the positions of the control points that I want you to use. The four locations are comprised of a cross hair mark (in the middle-left of the map), two side-ticks labeled 47'30", and the lower-right corner of the map neat line. The side-tick marks and the cross hair denote 2.5-minute marks. Do not be confused by the note in the margin of the map that reads, "(CENTER HALL 1:62,500)." It refers to a neighboring map from the 1:62,500 series. As I said above, the scale of the map that I scanned to produce the statecollege_map.tif image is 1:24,000.

3. Open the Link Table if it is not still open from your earlier work.

4. If the Link Table is not empty go to the Georeferencing dropdown list and choosing Delete Control Points.

5. This time disable the Auto Adjust by un-checking the box.

6. Open the map_utmControlPoints.txt found in your Lesson3 folder.

7. You can establish the temporary transformation links, just as you did for the DRG image (See Figure 3 and Figure 4) by creating the four links with dummy "To" values, then changing the XMap and YMap values in the Link Table to those found in the Xcoord and Ycoord columns of the map_utmControlPoints.txt file.

OR

8. Right-click instead of left-clicking to create the dummy "To" control points (the second click defining the control-point pair). This will bring up a box from which you can choose Input X and Y. Then you can change the values of the "To" control points to the UTM values listed in the text file as you create the control point pairs, instead of editing the Link Table. Not an earth-shatteringly different technique, but I wanted you to know about it. (Note, that once you initiate this method, were you to create subsequent "To" points by left-clicking in the map display area, as was done in the previous Section, the new "To" x-y values will be in UTM coordinates, not scanner coordinates, but will still need to be edited/replaced with the values from the map_utmControlPoints.txt file.)

9. After you have created the four control point links enable the Auto Adjust feature. The Residual list and the Total RMS Error should now become populated with meaningful values.

10. If necessary, update the display by using either Zoom to Layer, or the Full Extent tool.

11. If the map display area comes up empty (you may see only the control point cross hairs), and the check box next to the layer name is grayed out, change the Map: and Display: units to Meters.

How does the Total RMS Error look compared to what you got with the DRG? What about the Residuals? Are you able to improve upon the RMS error by deleting links and recreating them? In your Deliverables document discuss possible explanation(s) for why not.

12. Save the Link Table contents when you are satisfied that you cannot improve upon the RMS error.

13. Make your screen capture for the Deliverables!

14. Update Georeferencing.

15. Save the map document.

Again, If you want to re-georeference the image file, it is necessary to delete the world file, the .aux file and the .xml file (if using v.9.2), and to set up a new map document before doing so.

D. Define the coordinate system of the now-georeferenced image in ArcCatalog

Notice that I did not have you define the coordinate system of the data frame before you georeferenced the statecollege_map.tif image. We will now learn a second way to provide the coordinate system definition for a georeferenced image file. The statecollege_map.tif image file is georeferenced, and we know what the coordinate system is because we georeferenced it based on UTM values for the "To" control points. But, the GIS program does not know the coordinate system of the image file. (If you don't believe me, check the Properties of the statecollege_map.tif image.)

1. Now, in ArcCatalog, right-click on the statecollege_map.tif image file and select Properties.

2. Scroll down to the Spatial Reference section.

3. Click the Edit button.

4. Click the Select button.

5. Double-click on Projected Coordinate Systems.

6. Double-click on UTM.

The datum for this paper USGS topo sheet is NAD27:

7. Open the Nad 1927 list.

The State College, PA quadrangle is in UTM Zone 18 North:

8. Double-click, or highlight and Add, NAD 1927 UTM Zone 18N.prj.

9. Click OK twice to finish defining the coordinate system.

The coordinate system information you supply here is stored in the .tif.xml file that got created when you hit Update Georeferencing. (If you are using version 9.0/9.1 the .aux file gets updated with the coordinate system information.) So, if you delete the .tif.xml file (or the .aux file in the case of v9.0/9.1), you will lose the information that ArcMap needs in order to recognize the coordinate system of the image file.

After you define the coordinate system of the image file, you may be inquisitive enough to remove and then add the statecollege_map.tif image file back to your open ArcMap session. Before doing so, though, you should first go to the View menu in ArcCatalog and choose Refresh. If you do not do this, the image will come into your ArcMap session properly, but if you look at the Properties of the layer holding the image, the Spatial Reference property will display unknown, rather than show the description of UTM Zone 18 North, NAD27 coordinate system.

That is it for Part II

You have just completed Part II of this activity, which involved graphically/interactively adding "From" control points and explicitly adding "To" control points in order to georeference two images. In Part III, you will georeference an image by graphically adding both the "From" and the "To" control points.

This Try This! uses a copy of the statecollege_DRG.tif image file, and has you creating a new ArcMap document. You might want to come back to it AFTER you have completed Part III. I placed it here because of its relation to the image file you used above.

Try This! A. Prepare by making a copy of the image file and starting a new ArcMap session

1. In either My Computer or Windows Explorer make a new folder in your Lesson 3 folder called TryThis.

2. Make a copy of the statecollege_DRG.tif image file and place it in the new TryThis folder.

3. Open a new map document in ArcMap.

4. Add the statecollege_DRG.tif image file from your TryThis folder. Be certain NOT to add the statecollege_DRG.tif image file that resides in your Lesson3 folder.

5. Build the pyramids.

6. Define the coordinate system of the data frame to be UTM Zone 18 NAD27.

In neither of the two georeferencing exercises above, involving the two topo map images, did we alter the inherent coordinate system of the original image file. The crucial georeferencing information is contained in the XML file and in the world file (or, with 9.1, in the AUX file and in the world file). What if you do not want to

worry about keeping track of those files? The Rectify command will actually perform the georeferencing transformation, prescribed in the world file, on the pixels in the TIFF image file, creating a new image file in the process. The coordinate system of this new image file will no longer be that of the scanner platform, but will be the georeferenced coordinate system from which came the "To" control point coordinates. And as long as you have defined the coordinate system of the data frame prior to performing the georeferencing steps the new image file will retain the proper coordinate system name.

In this Try This! there are two versions of the Try This! B steps. The first is for those of you with version 9.2 of the software, the second is for those with v9.0/9.1.

Try This! B. Create a new georeferenced image that stands alone

If you are using version 9.2 of the ArcGIS software follow these steps. Otherwise, if you are using version 9.0 or 9.1 proceed with the steps in the Alternate Try This! B section, below. (You might want to read through the steps that are specific to version 9.2, since they reflect the current state of the software relative to this topic.)

1. This will be good practice: create the 4 control point pairs that will enable the Affine transformation (Steps II-A-9 through II-B-8). Don't forget to replace the "To" coordinate values.

2. DO NOT select the Update Georeferencing option!

3. Instead, once you are satisfied with your 4 control points choose Rectify from the Georeferencing drop down list.

4. Accept the default settings for Cell Size and Resample Type, but rationalize them to yourself.

5. For Output Location, browse to your Lesson3/TryThis folder. Set the Format to TIFF. You can accept the default Name which should be statecollege_DRG1.tif. (Make sure in the process of setting the name and output destination that the output file format does not change from TIFF.)

6. Click OK to save the image. This process may take some time. (We are creating a new, ~35Mb TIFF image. I think it took my machine about 4 minutes to process.)

7. If you look at the Spatial Reference properties of the statecollege_DRG1.tif image you should see that they reflect the UTM coordinate specifications that we assigned to the data frame.

How many new statecollege_DRG1.___ files are now in your Lesson3/TryThis folder? You should find a .tif file, along with a .aux, a .rrd and a .tif.vat.dbf file. If you move (make a copy to be safe) the new statecollege_DRG1.tif file, by itself, to another directory, then add it from there to a new, empty ArcMap session or to a new data frame, you will find that the data frame coordinate system has been defined as UTM. Try it and see. So, the new TIFF image is a stand-alone, georeferenced image file with a properly-defined coordinate system. Do you understand the difference between Update Georeferencing and Rectify as far as what files are created and where the georeferencing information is stored?

Alternate Try This! B. (For those using version 9.0/9.1) Create a new georeferenced image that stands alone

If you are using version 9.0/9.1 of the ArcGIS software follow these steps.

1. This will be good practice: create the 4 control point pairs that will enable the Affine transformation (Steps II-A-9 through II-B-8). Don't forget to replace the "To" coordinate values.

2. DO NOT select the Update Georeferencing option!

3. Instead, once you are satisfied with your 4 control points choose Rectify from the Georeferencing drop down list.

4. Accept the default settings for Cell Size and Resample Type, but rationalize them to yourself.

5. For Output Raster, browse to your Lesson3 folder and save the image in TIFF format as rectifystatecollege_DRG.tif.

6. Click OK to save the image.

7. If you look at the Spatial Reference properties of the rectifystatecollege_DRG.tif image you should see that they reflect the UTM coordinate specifications that we assigned to the data frame.

How many new rectifystatecollege_DRG.___ files are in your Lesson3/TryThis folder? Even though there are a world file and an auxiliary file accompanying the new TIFF image, you should be able to move (make a copy to be safe) the rectifystatecollege_drg.tif file, by itself, to a new folder, then add it from there to an new, empty ArcMap session and find that the data frame coordinate system has been defined as UTM. Try it and see. Do you understand the difference

between Update Georeferencing and Rectify as far as what files are created and where the georeferencing information is stored?

Lesson 3: Georeferencing Raster Images

Scenario: Georeferencing an Image for the Purpose of Data Creation

Part III: Georeferencing Using a Target Layer

A. Register the image

1. Open the Photo1963_<your name> map document.

2. Because, in Part I when you set up the data frame, you added the un-georeferenced air photo image file first to the data frame, the data frame coordinate system is undefined. (This behavior concerning how the coordinate system of the data frame is defined will be elaborated upon in Lesson 5.) If you look at the Properties of the StCol_Rds layer you will see that its coordinate system is State Plane Pennsylvania-North, NAD83 (the units are meters). Define the coordinate system of the data frame to match it.

3. In the Table of Contents, right-click on the StCol_Rds and select Zoom to Layer. This is the target layer in the context of what we are about to perform.

4. On the Georeferencing toolbar, confirm that StateCollege1963.jpg is selected as the Layer. (It will be, because it is the only image file in the data frame.)

5. Select Georeferencing > Fit to Display. Which ever image file (where there more than one in the Table of Contents) is named in the Layer window, is re-drawn so that it appears in the same coordinate space as the target data. [See Figure 5] (In this particular case the StateCollege1963.jpg entry is the only choice from which to choose in the Layer window.)

6. Change the color of the target layer so that it shows up clearly against the image background.

7. Open the Link Table, unless it is still there from Part II. Make certain that it is empty.

8. Enable Georeferencing > Auto Adjust.

This photo of State College, Pennsylvania was taken in 1963. Using the Control Points tool, you will define links FROM street intersections on the air photo image (StateCollege1963.jpg), TO the corresponding street intersection on the target roads layer (stcol_rds.shp). Links are established such that the air photo image location is clicked first, then its corresponding target location on the roads layer is clicked second. In a project like this, it is always helps if you are familiar with the study area. We have identified 5 street intersections that you can use as link locations:

o L1: College Ave/Corl St in the southwest corner

o L2: Curtin Rd/Porter Rd in the north-central part of the image near Beaver Stadium

o L3: Orchard Rd/Puddintown Rd in the northeast corner

o L4: S Atherton St/Allen St in the southeast corner

o L5: College Ave/Allen St near the center of the image

9. Visually locate these intersections on the image. Then, locate the corresponding intersection in the StCol_Rds layer. You will find it useful to turn on labels for the roads, labeling them with the contents of the name field. You could use the Identify tool to determine street names when you are zoomed in, if necessary.

If, when you zoom in on the image, it goes black try zooming in further to see if the definition of the image returns. If not, remove it and go to ArcCatalog and right-click on the image file and calculate the statistics. Then add the image back to the data frame.

In order to help define the links accurately, you can use the Magnifier window. You can decide. When placing the links, keep in mind that the roads layer represents the centerlines of the roads. Cross hairs have been placed on the image to help you determine where the roads layer and the image layer should coincide. [See Figure 6]

10. Click on the Add Control Points tool .

11. Select Window | Magnifier. Right click on the window title bar and select Properties. For the Modify main view by option (In v.9.2: Zoom | Magnify By:), select 1000% and click OK. (You can resize the Magnifier window. Zooming in or out on the data frame view effects what is magnified.)

12. Drag the Magnifier window so that the cross hairs line up with the landmark L1 in the image. Click on the intersection next to the L1 label.

13. Drag the window so that the cross hairs line up with the L1 intersection in the target layer. Click on the intersection. Because the Auto Adjust is enabled, the image will automatically adjust itself based on the established link. After establishing a link, the extent of the data frame may change such that parts of the image disappear. If necessary, use the Pan tool to change the extent of the data frame. Then, re-activate the Control Points tool to continue establishing links.

14. Repeat steps 11-12 for the other four control points in the target layer (L2-L5).

After each link is entered, the software adjusts the image as best it can to fit to all of the links. If you pan around the map, you will notice that some areas of the map have been adjusted more accurately than others. This is a function of the links that we have chosen to use. Five different links would result in a different pattern of accuracy.

Also, as you add transformation links pay attention to the Transformation: dropdown window at the bottom of the Link Table; see if/when it allows you to expand it to see more than just the 1st Order Polynomial (Affine) choice. After you create each new link, check to see how many choices there are. (Those of you using version 9.2 will notice that, after 3 links are added to the table, there will be an Adjust choice in the Transformation list. We will ignore that for now. If you are curious, search the Help on "Georeferencing image files.")

15. Note the RMS error reported in the bottom right of the Link Table window. Based on the information provided in the Concept Gallery, and knowing what you do about the image data involved in this part of the exercise, can you put much stock in the RMS error? Elaborate in the discussion you submit with your deliverable.

16. After you have created the 5 links from the points that were specifically indicated on the photo, continue to add links, paying attention to the Transformation: dropdown list.

Suggested intersections that may make reasonable additional link locations are:

o Park Av and Shortlidge Rd (though the curve in the road makes this an exercise in extrapolation)

o Westerly Py and Sparks St (the trees make this a challenge)

o Beaver Av and Allen St

After you have added 6 control point pairs does the choice list in the Transformation dropdown change? Opt for the new choice; select it. What is the new transformation choice? Make certain it is in your discussion deliverable.

17. Create a total of at least 7-8 links (including the original L1-L5 points). Be certain to pull out to Full Extent and witness what has happened to the once-rectangular image; look closely at the edges of the image--are they still straight?. Choosing the alternative to the affine transformation when it is first available will show an RMS error and residual values of 0 in the Link Table. This is similar to what happens when you have only 3 control point pairs when using the affine transformation. The residual values and the RMS error will appear when you have added more control point pairs.

18. Do not forget to make your screen capture, showing the transformation choice that you switched to after entering the 6th control point link.

19. In the Georeferencing dropdown, choose Update Georeferencing.

In version 9.2, with 2nd Order Polynomial picked as the Transformation: method, there will be a .jgwx file created. Ostensibly it is a world file. (In older versions of the software, because we are not using the affine transformation there is no world file created when we choose to Update Georeferencing.) However, this .jgwx file does not serve in the same capacity as does the world file associated with the results from using the Affine transformation: if you put this .jgwx file and the original .jpg image file in a folder by themselves the image file will NOT come in to the GIS in the proper coordinate space. The transformation equation coefficients for the higher-order transformation methods are stored in a .jpg.aux.xml file in the case of v9.2; and in the .aux file in the case of version 9.0/91.

20. Save the map document.

21. In ArcCatalog, check to see that the coordinate system information is associated with the statecollege1963.jpg file. You may need to View | Refresh. It should be, since we defined the coordinate system of the data frame in Step III-A-2.

Keep in mind that this photo has not been orthorectified. Orthorectification involves using elevation data to correct for the scale variations inherent in a vertical aerial photo. The workflow we are using in this project is best when applied to relatively flat areas. The positional accuracy of the image will decrease as the relief within the area increases. Because we usually want the most accurate data possible, most aerial photos you work with in the GIS field are not only georeferenced, but also orthorectified. (Orthorectification often implies that the photo is georeferenced, due to

the fact that the terrain model used in the rectification process is usually georeferenced.)

B. Deliverables

Project Evaluation criteria include:

Quality and Completeness: 90%A document that includes: three screen captures showing proof of having georeferenced three image files, description of a specific RMS error calculation, discussion of RMS error diagnostic value, and discussion of limiting factors when it comes to georeferencing image files. (See below.)

Timeliness: 10%Upload and submit the required content to the lesson drop box. Post by assigned due date. Most project deliverables are due on Thursdays, one week and a day from the official start of the assignment (two weeks and a day from the day the Lesson is available). Refer to the course calendar for the exact schedule. Please make every effort to submit your deliverables on time. Remember, to be consistent and fair we must deduct the 10% for late submissions, no matter what.

These deliverables are due two weeks after the Lesson is revealed. See the course Calendar for the specific due date.

1. A single Microsoft Word document should be submitted, containing all of the deliverables for this Lesson. (If you use WordPerfect please save as a .doc file before you submit. Please do not send a WordPerfect document. Please DO NOT submit a PowerPoint document.)

Incorporate your name into the name of your document file: something similar to "JSloan_Lesson3.doc" (your first initial and your last name).

Upload your document file to the Lesson 3 Drop Box - Don't forget to hit the Submit button!

Your document should contain the following, in the order specified:

a. Screen captures of the three data frames, taken where specified in the lesson write-up.

Each screen capture should show:

the ArcMap interface Table of Contents, so we can determine the activated layer.

the entire Link Table, so we can see the list of links and the Transformation method and RMS error.

the coordinate readout slot, at the bottom of the ArcMap interface window.

Your screen capture images need to be clear and comprehensible. Please do not include your desktop background as part of the image(s). (If you use the Print Screen button to capture the screen image, know that by holding down the Alt-key when hitting the Print Screen button you will be able to capture only the active window. This can help make your screen captures more space-efficient.) Switching the page format of your Word document to landscape orientation will allow for placement of wider images. The image file formats most often used include .png, .jpg, .gif, .bmp or .tif. Lastly, be sure to review your document in either a print layout view or the print preview (change zoom to 75%) before uploading and submitting.

b. Show how you calculated the threshold value of "an acceptable RMS error" that was called for in Part II Section B Step 7.

c. Based on the discussion in the Concept Gallery, and on the comments in the Lesson write-up, answer the following questions. The explanations asked for are important--we want to be certain you understand the concepts. Be succinct.

Does the RMS error that you ended up with for the statecollege_DRG.tif have any diagnostic value? Explain your answer. If it does, do you consider it acceptable? Explain why.

Does the RMS error that you ended up with for the statecollege_map.tif have any diagnostic value? Explain your answer. If it does, do you consider it acceptable? Explain why.

Does the RMS error that you ended up with for the vertical air photo of State College have any diagnostic value? Explain your answer.

If it does, do you consider it acceptable? Explain why.

d. List a minimum of 5 factors that might limit your ability to arrive at a low RMS error when georeferencing raster image data.

2. Make an entry in your e-Portfolio, reflecting upon the Lesson. (Do NOT post any of the specific results of the Lesson homework to your e-Portfolio web site.)

3. Take the Lesson 3 quiz.

That is it for Part III...and for Lesson 3

You have just completed Lesson 3. Do not forget...if you have any questions, feel free to post them to the Lesson 3 Message Board.

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