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GeoreferencingTutorial

Georeferencing

GEOREFERENCE

with

TNTmips®

and TNTedit™

Georeferencing

Before Getting Started

You can print or read this booklet in color from MicroImages’ Web site. TheWeb site is also your source for the newest tutorial booklets on other topics.You can download an installation guide, sample data, and the latest versionof TNTmips.

http://www.microimages.com

This tutorial introduces techniques for adding geographic control to your projectmaterials. You will use this Georeference process to define the spatial positionand coordinate reference system of your geodata objects. The TNT productsautomatically relate georeferenced objects to each other when they are displayed,measured, combined, and processed. Accurate georeferencing is an importantstep in preparing your geospatial materials for further use in the TNT products.

Prerequisite Skills This booklet assumes that you have completed the exercisesin the tutorial booklets Displaying Geospatial Data, TNT Product Concepts, andCoordinate Reference Systems. Those exercises introduce essential skills andbasic techniques that are not covered again here. Please consult those bookletsand other TNT reference materials (installed or on MicroImages’ web site) for anyreview you need.

Sample Data The exercises presented in this booklet use sample data that isdistributed with the TNT products. If you do not have access to a TNT productsDVD, you can download the data from MicroImages’ web site. In particular, thisbooklet uses sample files in the GEOREF and CB_DATA data collections. Make aread-write copy of those files on your hard drive; you may encounter problems ifyou work directly with the sample data on the DVD.

More Documentation This booklet is intended only as an introduction togeoreferencing geospatial data. A number of Technical Guides (installed and onMicroImages’ web site) provide further details and examples of georeferencingoperations.

TNTmips® Pro and TNTmips Free TNTmips (the Map and Image ProcessingSystem) comes in three versions: the professional version of TNTmips (TNTmipsPro), the low-cost TNTmips Basic version, and the TNTmips Free version. Allversions run exactly the same code from the TNT products DVD and have nearlythe same features. If you did not purchase the professional version (which re-quires a software license key) or TNTmips Basic, then TNTmips operates inTNTmips Free mode. All the exercises can be completed in TNTmips Free usingthe sample geodata provided.

Randall B. Smith, Ph.D., 5 January 2012©MicroImages, Inc., 2003-2012

Georeferencing

STEPSchoose Main /Georeference from theTNTmips menuin the Georeferencewindow, press theOpen icon button(or choose File /Open)select SEC32COMP fromthe SEC32G Project File

Starting Georeference

The exercises on pages 3-5introduce the Georeferenceprocess interface and theuse of reference objects.Exercises on pages 6-10show you how to positionand add control points usingsimple graphical tools.Concepts of residuals andresidual models arediscussed on pages 11 and12. Exercises on pages 13-15 show you how to select,delete, and edit controlpoints. Additional topicsand advanced features arediscussed on pages 15-19.

The Georeference process lets you create, edit, andstore control information that relates the positionsof raster cells and geometric elements in your spatialobjects to map coordinates in a specified coordinatereference system. Accurate georeferencing allowsyou to overlay a spatial object correctly with all yourother project materials.

In our first series of exercises you will work with ascanned color-infrared aerial photograph to add toand and improve its georeference. This raster ob-ject illustrates one of the most common types ofgeoreference information, control pointgeoreference. Control points are locations withinthe spatial object where map coordinates in somecoordinate reference system have been determinedand stored. Control points are most often deter-mined visually from other georeferenced data (thereference object). They are thus usually at loca-tions that can be recognized in both the input andreference objects. To get us started, our scannedphotograph has been provided with three controlpoints in the centers of road intersections near thecorners of the image.

TNTmips storesgeoreference controllinformation in ageoreference subobjectfor each spatial object.

The spatial object you select forgeoreferencing is automaticallydisplayed in the Georeference InputView. The input raster for this seriesof exercises has been provided withthree control points, shown by thenumbered cross symbols.

Georeferencing

The Control Point ListThe Georeference window is the control and information center for theGeoreference process. To start with we will focus on the center part of thiswindow, which shows a list of the current control points with columns listingcoordinates and other information for each point.

Each control point is assigned a number in the ID column; this ID is also shownin the Input View next to the point’s symbol. Each control point also has a pair ofobject coordinates that define its position using the internal coordinates nativeto the object. Since we are working with a raster object, the object coordinates inthis case are the fractional column and row positions within the raster, and theobject coordinate columns are thus labeled Column and Row. (If we weregeoreferencing a geometric object, these columns would be labeled Object X andObject Y.) Each point also has a pair of map coordinates that define the point’slocation in the specified coordinate reference system (CRS). Our sample rasterobject is georeferenced to the NAD83 / UTM zone 14N CRS (as shown above thepoint list) in which map coordinates are expressed as Easting and Northing (inmeters). These primary reference coordinate fields are therefore named Eastingand Northing.

To the right of the primary CRS fields is a pair of fields that show map coordinatesin an alternative secondary CRS, which defaults to a geographic (latitude/longi-tude) coordinate system using the same datum as the primary CRS. (In thisexample the datum is NAD83.) The secondary CRS columns in this case thushave headings Longitude and Latitude.

Object Coordinates Map Coordinates(Primary CRS)

Map Coordinates(Secondary CRS)

You can change the CRS used for the secondarymap coordinate columns by choosing Secondary CRSfrom the Georeference window’s Options menu.

Georeferencing

STEPSfrom the Options menuon the Georeferencewindow choose Show2D Reference Viewon the ReferenceView, press theAdd Layer icon buttonand select Quick-Addfrom the menuselect SEC32VEC from theSEC32G Project Fileon the Georeferencewindow’s toolbarpress the AddControl Pointsicon buttonopen the Georeferencewindow’s Options menuand make sure that theGeolock Views settingis toggled on

Choose a Reference ObjectTo improve the georeference for this aerial image weneed to add more control points. You can use anytype of accurately-georeferenced spatial object as areference object. Here we open a separateGeoreference Reference View and add a vector ob-ject as reference. This vector shows road centerlinesas black lines and property boundaries in cyan. Inthe portions of the scene that are occupied by agri-cultural fields, many of the property boundary linescoincide with vegetated fence lines that are visiblein the aerial image.

When you open an object that has existinggeoreference, as in this example, the Georeferencewindow’s default mode allows you to view controlpoints and edit their locations (more about editinglater). Press the Add Control Points icon button tochange modes to enable adding new points. Whenyou do so, the Crosshair tool is activated in both theInput and Reference views, and a crosshair appearscentered ineach view. When you turn on Add Control Points mode, the Crosshair tool is

automatically activated in the Input View and Reference View.

NOTE: View windows open with a sidebar that can show a legend, locator, andmagnifier. You can turn a view sidebar on and off using the Show/Hide Sidebar iconbutton. The views above are shown with the sidebars turned off to conserve space.

Georeferencing

The Crosshair ToolSTEPS

left-click on the titlebarof the Input Viewmove the cursor in theInput View to the roadintersection near thelower left corner of theimagepress 3 on yourkeyboard to zoom in tothat location in bothviewsin the Input View left-click at the center of theintersection to move thecrosshair to thatlocationuse the arrow keys onyour keyboard to adjustthe crosshair position ifnecessary

You use the crosshair tool to indicate correspond-ing control point positions in the Input View and theReference View. You can move the crosshair tool inseveral ways. You can left-click in the view to snapthe crosshair intersection to that location. You canalso drag the crosshair intersection to the desiredlocation. The arrow keys on your keyboard are use-ful for making fine adjustments in the crosshairlocations. When you move the cursor near one ofthe crosshair lines (but not near their intersection)the cursor changes from a cross to a double-arrowshape, allowing you to rotate the crosshairs to alignwith linear features in the view.

If you use the Zoom Box or Reposition tool in eitherview, remember to press the Corresponder tool iconbutton afterward to reactivate this tool. Instead ofswitching tools, you can use keystroke equivalentsto zoom and pan. You can see a list of availablekeystroke actions using the Hotkey button on ei-ther view. A view must be the active window inorder for you to use hotkeys for zooming at the cur-sor location.

The Geolock Views feature (on the Georef window’sOptions menu) is turned on by default, so that zoom-ing or panning one view automatically causes theequivalent action in the other view (if enough con-trol points exist to determine correspondinglocations).

Keyboard HotKeyscan be used forzooming and panningeither view at thecursor locationwithout deactivatingthe crosshair tool.

Crosshair positioned at the lower left road intersectionin the Input View (left) and Reference View (right).

Georeferencing

STEPSnote the estimated mapcoordinates for the newpoint in the control pointlistin the Reference Viewdrag the crosshairintersection to the road-line intersectionwhen both crosshairsare in correspondinglocations, pressthe Apply iconbutton on theGeoreference windowto add the control point

Estimate from ModelWhen you are adding points, the control point listautomatically includes an entry for the next point tobe added (shown with an * in the ID column). Notethat when you placed the crosshair in the Input View,the Reference View crosshair also changed position,and map coordinates appeared in red in the Easting,Northing, Longitude, and Latitude fields in the list-ing for this point. If you place the mouse cursorover this listing, a DataTip informs you that thesecoordinates were “Predicted from Model Solution”.

This behavior is the result when the Estimate fromModel icon button is turned on in the Referencesection of the Georeference window’s toolbar (thedefault condition). When the new point is initiallyplaced in the Input View, the reference coordinatesare automatically estimated based on the previously-placed points. When the same button is also turnedon for the Input View (also the default state), inputcoordinates are estimated automatically if you firstplace the new point manually in the Reference View.(Note that further adjustments of the point positionin either view do not trigger the estimation proce-dure.) This is a convenience feature; you shouldalways manually adjust the “estimated” position toprovide the best visual match between input andreference positions.

When you have moved the crosshair tool to thecorresponding positions in both Input and Refer-ence views, you add the new control point bypressing the Apply icon button on the Georeferencewindow or by simply right-clicking with the mouse.

Several “helper” modes toassist in placing controlpoints are selected usingicon buttons in the Input andReference toolbars on theGeoreference window.The default mode for both isEstimate from Model.

Estimate from Model

Georeferencing

Snap to Reference ElementsWhen you are using a geometric object as the refer-ence, two other Reference modes are useful: Snap toEnd or Point, and Snap to Vertex. When the inputcrosshair is moved in either view in these modes,the reference crosshair snaps to the relevant vectorfeature nearest the estimated position.

The Snap to End or Point mode snaps the crosshairto the nearest point element or to the nearest end ofa line element, which can include the intersection oftwo or more lines. Thus this mode is useful whenyou are using road intersections in a geometric ob-ject as reference locations, as in this exercise.

The Snap to Vertex modesnaps the crosshair tothe nearest vertex in thenearest geometric ele-ment in the referenceobject. Vertex locations are usually only evidentwhere there is a pronounced corner in a line elementor polygon boundary, as in the right-angle cornersof many property boundaries in our reference ob-ject.

STEPSzoom the viewsto full extentsin the active view,position the cursor nearthe road intersectionnorth of control point 3and press 2 to zoom inin the Reference groupin the Georeferencewindow’s toolbar, turnon the Snap toEnd or Point iconbutton

position the Inputcrosshair on the roadintersection

note that the crosshairin the Reference viewhas snapped to theexact intersection of thetwo black road lines

add thecontrolpoint

Snap to Endor Point

Snap toVertex

Snappedcoordinatesare alsoindicated incolor in thecontrol pointlist and by aDataTip.

Georeferencing

Overlay Mode and the Tie Point ToolSTEPS

zoom the Input View tofull extentspress the AddLayer icon buttonon the Input View andselect Quick-Add fromthe menuselect SEC32VEC from theSEC32G Project Filezoom the Input View into center of the image,near which twofencelines intersect atright anglesturn on theTie Point toolon the Input Viewposition the mouse onthe fence intersection inthe input imageleft-click and drag the ‘>’end of the tie point lineto the property lineintersection in thereference vectorrelease the mousebuttonadd the controlpoint

If the input object you are georeferencing has atleast three control points, you can add a referenceobject to the Input View as an overlay. Using anoverlay is very useful when the reference is a geo-metric object (vector, CAD, or shape). Using ageometric overlay allows you to visually comparethe registration of features in the input and refer-ence in any area, not just at the control pointlocations.

The Tie Point tool is provided for creating and edit-ing control points when you have a referenceoverlay. With the Tie Point tool active, you dragwith the mouse to create an elastic line in the InputView. The start of the line is marked with a crosssymbol (+), which corresponds to the control pointposition in the input object. The end of the TiePoint line is marked by an arrowhead symbol (>),which denotes the control point position in the ref-erence object.

IMPORTANT: always drag the Tie Point toolFROM the input object location TO thereference object location.

After you have drawn the tie pointline, you can adjust the position ofeither end of the line by dragging theend marker with the mouse. Whenthe Snap to End or Point mode is active for the refer-ence, you can drag the line close to the desiredreference line end or point, and the Tie Point tool’sreference end snaps to that feature.

Start draggingthe tie pointline at thecontrol pointlocation in theinput object.

Drag the tie point line to the referencecontrol point location, in this case theintersection of the property lines.

Georeferencing

Using a Reference RasterSTEPS

press the LayerManager iconbutton in the Input Viewin the Layer Manager,right-click on the listingfor the vector layer andchoose Remove Layerfrom the menu (you cando this instead in thesidebar legend if open)repeat for theReference Viewon the Reference View,press the AddLayer icon buttonand select SEC32G.RVC /SEC32ORTHO

turn on the Crosshairtool in either viewadd some more newcontrol points at roadand fence line junctions,with a goal of arelatively evendistribution ofpoints

You should now have five control points near theedges of the input image and one near the center.We can find additional control point locations usingan image as a reference. The new reference we aregoing to use is a color-composite raster (natural colorimage) extracted from orthoimage coverage of theregion. (An orthoimage has been processed to cor-rect distortions due to terrain and the geometry ofimage acquisition.)

Working with the Reference View, we can now usethe Crosshair tool as before to add more new controlpoints at features that we can recognize in both theinput and reference images. When you are startingwith an ungeoreferenced object, you should placethe initial control points at features near the outeredges and corners. Additional points should be dis-tributed as evenly as possible over the area of theobject.

Georeferencing

ResidualsSTEPS

turn off the AddControl Pointsicon buttonin the Georeferencewindow chooseOptions / Residual Units/ Metersnote the values in theResidual column and theRMS Residual values inthe Statistics panelchoose Options /Residual Units / Cells

The Georeference process provide a mathematicalassessment of the “quality” of control points in theform of residuals, or deviations from expected loca-tions as computed from a mathematical model. Aresidual model is an equation that transforms pointlocations between object coordinates and map co-ordinates in the specified CRS. You select themathematical form (complexity) of the equation us-ing the Model menu. The terms in the equation arethen computed automatically based on the controlpoint coordinates. Each form of residual model hasa minimum number of control points needed to sat-isfy the equation. Once the number of control pointsexceeds the minimum required, multiple solutions tothe equation are possible, and a “best fit” solutioncan be found, as described in the sidebar.

The Residual column in the control point list showsthe difference between modeled and actual pointpositions for each control point. This distance canbe shown in either object coordinates (cells for araster object) or in the distance unit characteristic ofthe specified CRS (meters in our example). The over-all residual for the entire set of control points,including its components in the X and Y directions,is shown in the Statistics panel.

The “best fit” solution to theresidual model has theminimum value for the RootMean Square (RMS) error:the square root of the meanof the squared residuals forthe individual control points.The individual control pointresiduals are the distancesbetween modeled andactual control pointlocations.

Residuals can beshown in objectcoordinates (left)or in CRScoordinate units(below).

Using cells as the residualunit provides a measurethat is independent of thecell size of the raster.

Georeferencing

Residual ModelsSTEPS

in the Options menu onthe Input View, makesure that the Warp toModel option is toggledonchoose Plane Projectivefrom the Model menu onthe Georeferencewindow

When the Warp to Modeloption is turned on for theInput View, the input objectis automatically reprojectedto the reference CRS usingthe current residual modeland control points.

High residual values for one or more control pointsmay result from errors in identifying correspondinglocations in the input and reference objects. How-ever, even when control points are “correctly” placed,high residuals may persist for some control points.For aerial and satellite images, high residuals mayresult from spatial shifts of image features by differ-ent amounts and in different directions (distortion)due to topography (relief displacement), a non-ver-tical angle of acquisition (tilt distortion), or the opticsof the imaging system.

The Georeference process provides a number of re-sidual models with different degrees of mathematicalcomplexity to account for different types of spatialdistortion that might be present in the data you aregeoreferencing. The minimum number of non-colin-ear points required to compute residuals increaseswith increasing model complexity. Some of the morecommonly used residual models are shown in thetable at the bottom of the page.

The aerial image we are georeferencing suffers fromtilt distortion and local relief displacement effects.

The Plane Projec-tive residual modelcompensates forthe tilt distortion,resulting in lowerresiduals com-pared to the defaultAffine model.

Use the Model menu tochoose the mathematicalform of the residual model.Using a model appropriatefor the input makes it easierto spot blunders in controlpoint placement.

Our control points show lower residuals when the PlaneProjective model is used rather than the Affine model.

AffinePlane ProjectiveOrder 2 Polynomial

346

Linear scaling in X and Y directions, rotation, shearProjection between non-parallel planes, models tilt distortionModels variable non-linear distortions

Model Minimum Points / Description

A sample of commonly-used residual models

For a full listing of residual models see the Technical Guide entitledGeoreference: Choosing a Model.

Georeferencing

Select, Disable and Enable Control PointsEach control point in the list has a checkbox controlon the left to disable or enable the point. Changingthe status of any point automatically causes a newresidual model to be computed using only the cur-rently enabled control points. You can thereforetoggle the status of individual points to assess theeffect on the residual values for other control pointsand the overall RMS residual value for all enabledpoints. Residuals continue to be shown for the dis-abled points, and are typically higher than forenabled points.

Enabled and disabled control points are shown inthe views in different colors. Points you have se-lected in the list are shown in a third color. You canassign colors for enabled, disabled, and selectedpoints by choosing Options / Colors from theGeoreference window. Selections on the ControlPoints menu allow you to enable or disable all points.

Disabling points allows you to identify problematicpoints that you may want to reposition or delete.You can delete any selected points using the Deleteicon button, or delete all disabled points using anoption on the Control Points menu.

STEPSleft-click on the list entryfor any control point toselect ithold down the Shift keywhile clicking on two listentries to select a rangeof pointshold down the Ctrl keywhile clicking on a listentry to toggle selectionon or offturn off the Enable/Disable checkbox forseveral points with highresidual values and notethe effect on residualsfor the enabled points

Select Colors window forselecting colors to indicatethe status of individualcontrol points in the views.

Control point listwith severalhigh-residualcontrol pointsdisabled.

You can select one or morecontrol points in the list fordeletion or other operations.

Georeferencing

Edit Control PointsWhen the Add Control Points mode is turned off,you can edit (adjust the position of) any existingcontrol point. You must first select the point to beedited in the control point list. The icon button forthe currently available placement tool (Crosshair orTie Point) then is activated in the Input View (andReference View if open) and can be turned on. Thenumbered control point symbol is then replaced inthe views by the tool graphic, allowing you to editthe point position graphically. The residual valuefor the point is automatically updated as you makechanges in the point position in either view, allow-ing you to preview the effect of your changes. Youcan also edit any of the coordinate values for thepoint directly in its fields in the control point list.

When you have finished editing the point, pressingthe Apply button accepts your changes. If you se-lect another point in the list before applying thechanges, a dialog window pops up to ask whetheryou want to apply the changes to the active point.

When the viewsare zoomed in,selecting adifferent point toedit automaticallyzooms bothviews to thenewly selectedpoint.

STEPSchoose Enable All fromthe Control Points menuzoom in on a controlpoint with a highresidual valueleft-click on that point’sentry in the control pointlist to select itturn on the Crosshairtooladjust the point positionin the Input orReference view (orboth)press Apply toaccept thechanges

when you are satisfiedwith the set of controlpoints, pressSave to save thegeoreference subobject

Georeferencing

Raster / Raster OverlaySTEPS

open raster COMP2from the SEC32G

Project File as the inputobjecton the Input View,choose Options /Raster/Raster Overlay /Green-Redin the Input Viewsidebar legend or LayerManager, click on theraster layer name tomake it the active layeradd the SEC32ORTHO

raster from theSEC32G Project File to theInput Viewpress the AddControl Pointsicon button on theGeoreference windowturn on the TiePoint tool in theInput View

Input raster ingreen-scale

Reference rasterin red-scale

Overlay of reference and input rasters usingGreen-Red color scheme.

Bright road features in Green-Red:

Good registration:bright roadscoincide as yellow.

Poor registration:offset green andred road features.

When both the input and reference are raster ob-jects, you can add the reference raster as an overlayin the Input View. You can add the overlay in one ofa number of special display modes that show theinput raster and the partially-transparent referenceoverlay in shades of separate complementary col-ors. Different color combinations may work betterthan others for particular images, depending on theimage colors present; you can easily switch combi-nations until you find one that shows features clearlyin both images. In this exercise we use green shadesfor the input image and red shades for the reference.In places where bright features (such as the roads)are well-aligned, the green and red add to create yel-low. Where the images are misaligned, color fringesor offset duplicate features are visible.

You also have the option to overlay the reference infull color. When you use that option, be sure toopen the Raster Layer Controls for the reference andon the Options panel set a transparency value forthe overlay.

With the referenceraster overlay in theInput View, you usethe Tie Point tool toadd and edit controlpoints, just as youdid with a referencevector overlay.

Georeferencing

Multiband Image InputSTEPS

press the Openicon buttonnavigate to the CB_DATA

data collection and intothe CB_TM Project Filechoose rasters BLUE,GREEN, RED, PHOTO_IR,TM_5, and TM_7press [OK] on theDisplay Bands dialogthat openson the Georeferencewindow pressthe Image BandCombination icon buttonin the Display Bandsdialog, choose TM_7 forRed, PHOTO_IR for Green,and GREEN for Blue

You can select and simultaneously georeference allbands of a multiband image that have the same cellsize and dimensions. After you select the rasterobjects, you are automatically prompted to chooseany single band or any 3-band RGB combination ofbands to display in the Georeference Input View.(You can change this display combination at anytime using the Image Band Combination icon buttonon the Georeference window.) When you savegeoreference information, it is automatically savedto all of the selected image bands.

The Georeference process by defaultshows only the total residual for eachpoint in the control point list. You canadd columns for X and Y residualsfrom a dialog opened by choosingOptions / Columns. You can alsochoose whether to show columns forelevation, the secondary CRS coordi-nate columns, and a point name field.

from the Options menuin the Georeferencewindow, chooseColumnsin the Choose Columnsdialog window, turn onthe toggle buttons forResidual X andResidual Y

If there are bands named Red,Green, and Blue, the DisplayBands dialog automaticallyassigns them to thecorresponding color channelfor display. However, youcan choose any RGBcombination of the bands todisplay in the Input View.

Added columns for X and Y residuals

Georeferencing

Ungeoreferenced InputSTEPS

in the Georeferencewindow, openraster SIMPLE.RVC /LKMEAD from the GEOREF

data collectionin the CoordinateReference Systemwindow that opens,expand the Global andRegional group on thePredefined tabbed panelexpand the UniversalTransverse Mercator(UTM) subgroupscroll down and selectUTM zone 11N (CM 117)press [OK] in theCoordinate ReferenceSystem windowin the Selectgeoreference modelwindow that opens,note the explanationsfor the availablegeoreference models

keep the Selectgeoreference modelwindow open andproceed to the nextexercise

In the Georeference process, selecting a spatial ob-ject lacking georeference as input triggers theappearance of a sequence of dialog windows. TheCoordinate Reference System window appears first,enabling you to designate the spatial referencingsystem (datum and coordinate system) to use togeoreference the object. This is the standard dialogwindow used throughout the TNT products for thispurpose (see the Tutorial entitled Coordinate Ref-erence Systems for further details).

After you set the coordinate reference system, theSelect georeference model window appears and pre-sents the georeference models available for the typeof input object you have selected. A description ofthe selected model appears in the right side of thiswindow to provide context for your choice.

Expand the Globaland Regional group...

then the UniversalTransverse Mercatorsubgroup...

then choose theindicated UTM zone.

Explanations are providedfor the georefence modelsin the Select georeferencemodel window.

Georeferencing

Simple GeoreferenceSTEPS

choose Simple on theSelect georeferencemodel window andpress [OK]in the Create SimpleImage Georeferencewindow that appears,enter 30 in the Columnand Row fields in theCell Size groupboxchoose Upper LeftCorner from the ImageLocation menuin the Coordinatesgroupbox, enter 707280in the Easting Fieldenter 4013640 in theNorthing fieldkeep the default settingof Projection Upright onthe Orientation menupress [OK] on theCreate Simple ImageGeoreference window

The choice of Simple georeferenceis integrated with georeferencemodel selection.

To set up Simple georeference specify the raster cellsize, the reference point location in the image, itsreference coordinates, and the image orientation.

The reference location in this exampleis the upper left corner of the image.

In some cases you may acquire images withgeoreference information only in a nonstandardmetadata or text file that cannot be automaticallyparsed by TNTmips during import. This georeferenceinformation is most often in the form of simplegeoreference, which specifies the size of image cellsand the reference coordinates for a designated ref-erence point in the image (most commonly the upperleft corner). In most cases image rows and columnsare exactly aligned to the map grid of the coordinatereference system (projection upright), but other ori-entations can be specified as well.

The choice of simple georeference is presented inthe Select georeference model window as an alter-native to designating a residual model for controlpoint georeference. You can then enter the requiredparameters in the Create Simple Image Georeferencewindow. When all parameters have been set andyou press OK on this window, affine georeferenceparameters are computed and automatically savedfor the input object, completing the process.

Georeferencing

Advanced FeaturesAuto-Register Creating georeference control points manually for a large aerialor satellite image to improve its registration to reference geodata can be a time-consuming task. The Auto-Register operation in the Georeference processautomatically generates hundreds to thousands of control points for an inputimage using a reference image of the same area. The reference image you usedoes not have to match the cell size, coordinate reference system, or extents ofthe input image. The reference image can be a single grayscale raster, an RGBdisplay of separate image bands, or a color-composite raster. It can reside in aTNT Project File, any image file format supported for direct use (GeoTIFF, GeoJP2,...), or in a standard web tileset structure (Google Maps, Google Earth, or BingMaps) on your local network or on the web, including the publicly-available webtilesets hosted by MicroImages. For accurate results you should use a referenceimage with spatial resolution equal to or better than that of the input.

Import GPS Control Points If ground control points have been acquired in aGPS survey over the area of your input data, the GPS points can be importeddirectly from standard GPX, CSV, or text files to use as georeference controlpoints. Map coordinates from a GPX file are automatically converted to thereference coordinate reference system if necessary.

Snap to Map Grid For input objects that include map grid lines or grid intersec-tion tick marks, such as scanned topographic maps, the Snap to Grid mode on theReference toolbar lets you quickly enter control points with the appropriate mapcoordinates. You define a virtual map grid that specifies the coordinate referencesystem and grid line spacings found in the input object. Once the virtual grid isestablished, placing the Crosshair tool in the Input View automatically sets thatcontrol point’s map coordinates to those of the nearest virtual grid intersection.

Transfer Georeference Some satellite images include image bands with differ-ent spatial resolutions (cell sizes). Once you have georeferenced thehigher-resolution bands, the Transfer Georeference operation in the Georeferenceprocess allows you to transfer that georeference to the lower-resolution bands,with appropriate adjustments for the differing cell sizes.

More information about these and other features can be found in the a series ofGeoreference Technical Guides available at microimages.com, including:

Auto-Register to Reference ImageAuto-Register Landsat 5 to a Global Web TilesetImport GPS Control Points from GPX FileSnap Control Points to Elements or Reference GridMultiband and Multiresolution Images

OverviewChoosing a ModelControl Point ListSimple and Implied

GeoreferencingAdvanced Software for Geospatial Analysis

MicroImages, Inc.

MicroImages, Inc. publishes a complete line of professional software for advanced geospatialdata visualization, analysis, and publishing. Contact us or visit our web site for detailed productinformation.

TNTmips Pro TNTmips Pro is a professional system for fully integrated GIS, imageanalysis, CAD, TIN, desktop cartography, and geospatial database management.

TNTmips Basic TNTmips Basic is a low-cost version of TNTmips for small projects.

TNTmips Free TNTmips Free is a free version of TNTmips for students and profession-als with small projects. You can download TNTmips Free from MicroImages’ web site.

TNTedit TNTedit provides interactive tools to create, georeference, and edit vector, image,CAD, TIN, and relational database project materials in a wide variety of formats.

TNTview TNTview has the same powerful display features as TNTmips and is perfect forthose who do not need the technical processing and preparation features of TNTmips.

TNTatlas TNTatlas lets you publish and distribute your spatial project materials on CD orDVD at low cost. TNTatlas CDs/DVDs can be used on any popular computing platform.

Index

GEOREFERENCE

Add Control Points mode................5-13,15advanced features.................................19auto-register.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19control point...........................3-5,9-14control point list....................4,7,11,13,14Control Points menu......................13,14coordinate reference system....2,4,11,17,19Crosshair tool..........................5-8,10,14,19disable control point.............................13edit control points..............................14enable control point................................13Estimate from Model................................7Geolock views..................................5,6hotkeys.............................................6import GPS control points.....................19Input View..........3,5-7,9-10,12,14-16,19map coordinates..................................4multiband image...............................16,19

object coordinates................................4overlay mode................................9,15raster/raster overlay.......................15reference object...............3,5,8-10,12reference view......................5-7,10,14residual model.................11-13,17,18residuals . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-14,16s a v e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4SelectColors window.......................13select control point..........................13simple georeference........................18Snap to End or Point.....................8,9Snap to Map Grid..............................19Snap to Vertex.................................8Tie Point tool..........................9,14,15Transfer Georeference.....................19Warp to Model..................................12

e tutorial e r e georeferencing - microimages, inc....georeferencing a geometric object, these...

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