arcgis workflows

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ArcGis workflows From website: (Goes from lesson 1 thru 6)Lesson 3: Georeferencing Raster Images Scenario: Registering an Image for the Purpose of Data CreationIntroductionA. 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. 2. 3.

Georeference a USGS DRG. Georeference a scanned USGS paper topographic quadrangle. 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.

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 file you could download these four. 23 KB, it'll take 3 seconds ~2.6 MB, approximately 6 minutes via modem ~3.2 MB, approximately 7.5 minutes via modem ~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 CreationPart I: Getting StartedA. Organize the data - Create three map documents In this section you will set up 3 map documents. 1. 2. Open ArcCatalog.

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 pyramid


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