Image Orthorectification

This chapter explains how to use the ER Mapper Geocoding wizard to geometrically correct rawimage data and orthorectify it to real-world coordinate systems and map projections.

Orthorectification corrects local and global distortions in an image by adjusting for cameracharacteristics, platform positions, and terrain details.

The camera characteristics, derived from a camera calibration report, are stored in a camera filefor use by the Geocoding wizard.

The terrain details are supplied in the form of a DEM. If the terrain is relatively flat, you can usean average height value.

In the case of advanced orthorectification, the platform position is determined by exteriororientation values that describe the exact position of the aircraft at the time the image wastaken, and how this relates to the image. The following parameters are specified:

• Attitude Omega – The tilt angle (roll) of the aircraft, which is the rotation about the X axis(direction of travel).

• Attitude Phi – The swing angle (pitch) of the aircraft, which is the rotation about the Y axis.

• Attitude Kappa – The azimuth angle (yaw) of the aircraft, which is the rotation about the Zaxis.

• Exposure Center XYZ – The coordinates of the exposure center of the image.

If the exterior orientation parameters are not known, you must specify 4 to 6 GCPs for theGridding wizard to compute them.

To use orthorectification you must have the following information available:

• Camera file containing camera calibration information

• DEM file (you can enter an average height if the terrain is relatively flat)

• Exterior orientation (Only for advanced orthorectification; otherwise, you must select GCPs)

• GCPs referenced by their XYZ coordinates.

The diagram below illustrates the required inputs for orthorectification.

Image Orthorectification file:///C:/Program Files/Intergraph/ERDAS IMAGINE 2013/ERMHELP/...

1 de 27 23/06/2013 14:10

These exercises give you practice using ER Mapper’s Geocoding wizard to orthorectify animage.

After completing the exercises, you know how to perform these tasks in ER Mapper:

• Use the Geocoding wizard to orthorectify an airphoto

• Use the Camera wizard to create a camera file from a calibration report

• Locate fiducial marks on an airphoto

• Select suitable ground control points

Before beginning these exercises, make sure all ER Mapper image windows areclosed. Only the ER Mapper main menu should be open.

Note: In these exercises, you use the Geocoding wizard to orthorectify an airphoto image ofSan Diego taken in 1997. The example images are used with permission from Aerial Fotobank.

In this exercise, you learn how to use the Geocoding wizard to orthorectify an airphoto. You alsolearn how to use the Camera wizard to create a Camera file with given calibration parameters.

Opening the Geocoding Wizard


2 de 27 23/06/2013 14:10

To open the Geocoding wizard, follow these steps:

1. Click the Ortho and Geocoding Wizard button on the Common Functions toolbar.

The Geocoding wizard opens with the Start tab selected.

2. Click the Load Algorithm or Dataset button in the Input File section to open the filechooser.

3. Select the path ending with examples from the directories drop-down list.

4. Double-click the ermapper directory to open it.

5. Double-click the Applications directory to open it.

6. Double-click the Airphoto directory to open it.

7. Double-click the 1_Geocoding directory to open it.

8. Double-click the San_Diego_Airphoto_34_not_rectified.ers file to select it.

9. Click the Orthorectify Using Ground Control Points button.

Note: In this example, you do not have exterior orientation parameters that provideinformation on the position of the platform or aircraft. Instead, you select GCPs so that thewizard can compute the exterior orientation parameters. If these parameters are available,you can select the Orthorectify using Exterior Orientation option.

10. Click the Ortho Setup tab.

Entering Terrain and Camera Details

The Ortho Setup tab lets you enter the terrain details in the form of a DEM or as an averageheight value. Obviously, using a DEM produces a more accurate result. However, if the terrain isrelatively flat, you can enter an average value. In this example, you enter the name of a DEMfile.


3 de 27 23/06/2013 14:10

You supply the camera details to the Geocoding wizard in the form of a camera file. If theapplicable camera file does not exist, you can use the Camera wizard to create one.

To enter terrain and camera details, follow these steps:

1. Click the Use a DEM file as Height button in the DEM Setup section.

Note: The DEM Setup section changes according to the option that you choose. Becauseyou selected the Use a DEM File as Height option, the DEM Setup section displays a fileand a band chooser for you to select the DEM file and the required data band.

2. Click the Load Input DEM File button to open the file chooser.





7. Double-click the 1_Geocoding directory to load it.

8. Select the San_Diego_DEM.ers file to open it.

9. Click OK to return to the Geocoding wizard.

10. Click the Camera Wizard button in the Camera Details section to open the CameraWizard dialog.

Creating Camera Files

The Camera wizard creates a camera file for the Geocoding wizard to use. It does this byproviding a number of dialogs for you enter camera calibration information. You normally get this


4 de 27 23/06/2013 14:10

information from a camera calibration report. If you do not have a valid calibration report for thecamera that was used to take the image, you can use a generic report for that camera model.However, this could result in some inaccuracies.

To create a camera file, follow these steps:

1. Click the Create New button on the Introduction page in the Camera wizard to create anew camera file.

Note: You can choose to edit an existing camera file, in which case the wizard provides youwith a Camera File field and chooser to enter the name of the existing file.

2. Click the Next button to go to the Camera Identification page.

Note: The information you enter here is not used by the Geocoding wizard. It is, however, agood idea to include it because it is a means of identifying the camera and the calibrationreport in the future.

3. Enter the following information in the applicable fields:


5 de 27 23/06/2013 14:10

• Manufacturer – Wild

• Model – RC20

• Lens Serial Number – 13115

• Date Calibrated – Day: 31, Month:10, Year: 1998

4. Click the Next button to go to the Camera Attributes page.

Note: Use this page to enter information on the focal length of the camera lens. In addition,you can enter information on the position of the principal point relative to the lens center as ameasure of lens distortion. Any distortion in the lens would cause the principal point to beoffset from the lens center.

5. Enter the following information in the applicable fields:

• Focal Length – 152.793

• X Offset to Principal Point – 0

• Y Offset to Principal Point – 0

6. Click the Next button to go to the Number of Fiducial Points page.


6 de 27 23/06/2013 14:10

Aerial photography cameras insert fiducial marks around the edges of the airphoto images.The Geocoding wizard uses the positions of these marks to relate the image to the cameramodel.

Note: Different cameras insert these marks in different places on the image. Use this pageto specify where the camera has placed the Fiducial marks. If you specify four fiducial markswhere the camera has, in fact, inserted eight, the Geocoding wizard only takes intoconsideration the four you specified.

7. Click the All 8 button.

This indicates that the fiducial points are on the four corners and the middle of edges of theimage.

8. Click the Next button to go to the Fiducial Point Offsets page.

This page lets you specify the positions of the fiducial points relative to the principal point.

9. Enter the following values in the applicable fields:

• Top Left – X:-105.99 Y:106.01


7 de 27 23/06/2013 14:10

• Middle Top – X: 0.011 Y: 110.01

• Top Right – X:106.01 Y:106.02

• Middle Left – X:-109.99 Y: 0.012

• Middle Right – X:110.01 Y: 0.013

• Bottom Left – X:-105.99 Y:-105.99

• Middle Bottom – X: -0.005 Y: -109.99

• Bottom Right – X:106.01 Y:-105.99

10. Click the Next button to go to the Finish page.

11. Click the Save button in the Camera File field to select a directory and file name towhich to save the new camera file.

12. Select the path ending with examples from the Directories menu.


14. Double-click the Miscellaneous directory to open it.

15. Double-click the Tutorial directory to open it.

16. Type camera_<your initials> in the Save As field.

17. Click the OK button to return to the Camera wizard.

The file name and directory you entered displays in the Camera File field.

18. Click the Finish button to return to the Geocoding wizard.

19. Click the Load Camera File button in the Geocoding wizard Camera File field toopen the file chooser.


8 de 27 23/06/2013 14:10

20. Select the path ending with examples from the Directories menu.




24. Double-click the camera_<your initials> file you saved to load it.

Editing Fiducial Points

The Fiducial Point Edit tab lets you enter the locations of the fiducial points on the image intoER Mapper.

1. Click the Fiducial Point Edit tab.

ER mapper opens two image windows: one in ZOOM mode and the other in OVERVIEWROAM mode.

2. Check the Auto Zoom check box on the Fiducial Point Edit tab.

This causes the ZOOM window to automatically zoom to the selected fiducial mark.


9 de 27 23/06/2013 14:10

3. Select the Pointer Tool on the Standard toolbar.

4. Click Top Left in the Name column in the table on the Fiducial Point Edit tab.

5. Click the fiducial mark in the top-left corner of the image in the OVERVIEW ROAM window.

The image in the ZOOM window automatically zooms to the selected fiducial mark. Use thisto adjust the position of the cursor to the center of the red circle.

6. Click Top Right in the Name column in the table.

7. Click the fiducial mark in the top-right corner of the image in the OVERVIEW ROAMwindow.


8. Click Bottom Left in the Name column in the table.

9. Click the fiducial mark in the bottom-left corner of the image in the OVERVIEW ROAMwindow.


10. Click Bottom Right in the Name column in the table.

11. Click the fiducial mark in the bottom-right corner of the image in the OVERVIEW ROAMwindow.


12. Click Middle Left in the Name column in the table.

13. Click the fiducial mark in the middle of the left side of the image in the OVERVIEW ROAMwindow.


14. Click Middle Right in the Name column in the table.

15. Click the fiducial mark in the middle of the right side of the image in the OVERVIEWROAM window.


16. Click Middle Top in the Name column in the table.

17. Click the fiducial mark in the middle of the top of the image in the OVERVIEW ROAMwindow.


18. Click Middle Bottom in the Name column in the table.

19. Click the fiducial mark in the middle of the bottom of the image in the OVERVIEW ROAMwindow.


10 de 27 23/06/2013 14:10


After selecting the fiducial markers, the table on the Fiducial Point Edit tab should be similarto what is shown below.

The RMS column displays values of less than 1.00.

The image window should now have all the fiducial points labeled.

20. Check the Errors check box on the Fiducial Point Edit tab.

21. Adjust the position of the selections in the direction of the indicated errors.

The x10 option enlarges the error markers for a more accurate indication.

Setting up GCPs

The GCP Setup tab lets you specify the way that you want to choose control points. You canenter control points manually, chosen from a reference image, chosen from a digitizing tablet, orchosen using a combination of these three methods.


11 de 27 23/06/2013 14:10

In this exercise, you use a previously orthorectified reference image to locate GCPs.

To set up ground control points, follow these steps:

1. Click the GCP Setup tab.


12 de 27 23/06/2013 14:10

2. Click the Geocoded Image, Vectors or Algorithm check box.

This tells ER Mapper you plan to select corresponding points between two images on thescreen.

3. Click the Load Corrected Algorithm or Dataset button.

4. Select ER Mapper Raster Dataset (.ers) from the Files of Type drop-down list.






10. Double-click the San_Diego_Airphoto_34_rectified.ers image to load it.

This is the already rectified image containing coordinate information.

Setting up Parameters for Image Rectification

The Datum, Projection, and Coordsys Description fields in the Output Coordinate Space sectiondisplay the coordinate system of the output rectified file. These parameters are includedautomatically from the CORRECTED (rectified) Airphoto image.

The Datumshift Code field displays the datumshift method used for reprojection. Normally, the


13 de 27 23/06/2013 14:10

default method is fine. You can click the Change Datumshift Code button to change it whengoing from NAD27 to NAD83(HARN) because the method is specific to each state.

To set up parameters for the image rectification, follow these steps:

1. Click the Choose Coordinate System button.

The ERMapper Coordinate System Chooser dialog opens showing available coordinatesystems.

2. Change the settings to what is displayed above, if necessary.

3. Click OK to close the ERMapper Coordinate System Chooser dialog.

Editing GCPs

The GCP Edit tab lets you edit ground control points.


14 de 27 23/06/2013 14:10

Selecting GCPs in the Upper-Left of Images

Note: Make sure the main ER Mapper menu is not hidden by the image window before startingthis exercise. You should move it slightly, if needed, so you can easily access the toolbars.

To select a ground control point in the upper-left portion of both images, follow these steps:

1. Click the GCP Edit tab.

ER Mapper opens several image windows and dialogs. You should see a screen setupsimilar to this one:

If your system does not position the windows automatically, rearrange them as shownabove before proceeding.


15 de 27 23/06/2013 14:10

2. Check the Auto Zoom check box on the GCP Edit tab.

The ZOOM windows automatically zooms in to the point selected in the correspondingOVERVIEW ROAM windows.

3. Click a well-defined feature in the UNCORRECTED GCP (OVERVIEW ROAM geolink)window to select it.

The UNCORRECTED GCP ZOOM window zooms in to the selected point.

4. Click once in the CORRECTED GCP (OVERVIEW ROAM geolink) window to activate it,and then click the same feature to select it as a GCP.

The CORRECTED GCP ZOOM window zooms in to the selected point.

5. Use the two ZOOM windows to adjust the positions of the ground control point.

You have now selected a ground control point in the image.

Selecting a Second GCP in the Lower-Left of Images

To select a second ground control point in the lower-left portion of both images, follow thesesteps:

1. Click the Add New GCP button on the Edit GCP tab.

2. Click a well-defined feature in the UNCORRECTED GCP (OVERVIEW ROAM geolink)window to select it.

The UNCORRECTED GCP ZOOM window zooms in to the selected point.

3. Click in the CORRECTED GCP (OVERVIEW ROAM geolink) window to activate it, andthen click the same feature to select it as a ground control point.

The CORRECTED GCP ZOOM window zooms in to the selected point.

4. Use the two ZOOM windows to adjust the positions of the ground control point.

You have now selected a second ground control point in the image.

5. Select four more ground control points near the upper-right, lower-right, and middle of theimages using the steps above.

The more ground control points you select, the lower the possibility of errors. You need atleast six for orthorectification.

Using Other Features on the GCP Edit Tab

To use other features on the GCP Edit tab on the Goecoding wizard, follow these steps:

1. Click any ground control point number in the Name column in the table on the GCP Edittab.

ER Mapper moves the crosshairs to select that point in all the OVERVIEW ROAM andZOOM windows.

2. Clear the Auto Zoom check box to turn it off.

3. Click any ground control point number in the Name column.

ER Mapper moves the crosshairs to select that point in the OVERVIEW ROAM windows, butnot the ZOOM windows.


16 de 27 23/06/2013 14:10

4. Click the Zoom to Current GCP button.

ER Mapper zooms in to the selected ground control point in the ZOOM windows.

5. Delete the number text for a ground control point in the Name column, and type a shortname.

Note: You can give ground control points text labels as well as numbers to help identifythem.

6. Click On in the second column for any ground control point.

The text changes to Off and all the RMS errors are recomputed without including thatground control point. This is an easy way to see how the positional error of any groundcontrol point influences the RMS of the others. For example, turning off a ground controlpoint with a large RMS often reduces the RMS of the others. Also, this can be importantwhen choosing which ground control points to use for the final image rectification.

7. Turn off other ground control points to see the effect, but turn all on again when finished.

8. Click Edit in the third column for any ground control point.

The text changes to No and the X and number marking it in the image turns green. Thiseffectively locks a ground control point so it cannot be edited (that is, clicking in the imagewindows do not redefine its position). This is useful when you have several very goodground control points, and you need to lock them to avoid accidentally changing them.

9. Check the Errors check box.

The magnitude and direction of the calculated positional error are shown graphically by aline for each ground control point on the image. If you have very small RMS errors, youmight not see the error line even if you increase the line length by a factor of 10 using thex10 option.

10. Check the Grid check box.

A polynomial grid displays over all three image windows. This grid is a preview of the way inwhich the FROM (raw) image pixels are reprojected onto the new coordinate grid of the TOimage. This grid is only an approximation, because the lines are actually curved.

11. Click the Add New GCP button and select a point on the CORRECTED image.

12. Click the Calculate Uncorrected Point button. The wizard automatically positions thecorresponding ground control point on the UNCORRECTED image.

13. Use the ZOOM windows to adjust the ground control point position.

This facility is available once you have positioned four points.

14. Click Save in the Geocoding wizard dialog.

15. Click Yes when asked confirm saving the GCPs to disk.

This saves the geocoding information into the header file of the UNCORRECTED image.

Rectifying Images

This tab lets you rectify images.


17 de 27 23/06/2013 14:10

To rectify the image, follow these steps:

1. Click the Rectify tab.

2. Click the file chooser button for the File field.





7. Type a name for the file in the Save As field using your initials at the beginning, and thenclick OK. For example, type:

CK_Airphoto_orthorectified

8. Click the Edit Extents button to open the Geocode Output Extents dialog.


18 de 27 23/06/2013 14:10

This dialog lets you specify how much of the orthorectified image you want to save. You havethree main options:

• Maximum Extents – Saves the whole image including any portion not visible in the currentlyactive image window.

• Optimum Extents – Automatically calculates the extents of airphotos to exclude the blackedges around them.

• Custom Extents – Lets you specify the top-left and bottom-right coordinates of the area toinclude. If you click the Snapshot button, ER Mapper selects the extents of the visible part ofthe image in the currently active image window.

9. Click the Optimum Extents button to remove the black edges.


11. Select Nearest Neighbor from the Resampling drop-down list on the Rectify tab.

Note: The Cell Attributes box also lets you resample the output image to a different cell size(Output Cell width and height), and specify a null cell value.

12. Click Save to save the orthorectification parameters in the San_Diego_Airphoto_34_not_rectified.ers header file.

13. Check the Display Rectified Image check box to display the image after it is rectified.

14. Click the Save File and Start Rectification button.

ER Mapper opens a status dialog to indicate the progress of the rectification.

15. Click OK when the operation finishes.

16. Click the Close button to exit the Geocoding wizard.

You have rectified the uncorrected airphoto image to correspond to the 1927 North American


19 de 27 23/06/2013 14:10

Datum (NAD27) and UTM zone 11 (NUTM11) map projection.

Note: Do not close the image window with the orthorectified image

Evaluating Image Orthorectification

To evaluate the image orthorectification, follow these steps:

1. Click the Edit Algorithm button on the Common Functions toolbar to open theAlgorithm dialog.

The Algorithm dialog displays the Red, Green, and Blue layers of the orthorectified image<your initials>_Airphoto_orthorectified.

2. Click the Blue Layer in the Algorithm dialog to select it.

3. Click the Load Dataset button in the algorithm process diagram.






9. Click the San_Diego_Airphoto_34 _rectified.ers image to select it.

10. Click the OK this Layer Only button to load it into the Blue layer.

Note: The Red and Green layers should still have the <your initials>_Airphoto_orthorectifiedimage.

11. Select B3:Blue from the band selection drop-down list for the Blue layer.

Displaying Images to Evaluate Registration

To display the two images to evaluate registration, follow these steps:

1. Click the Refresh Image with 99% Clip on Limits button in the Algorithm dialog.

This image combines two different images: one in the Red and Green layers and one in theBlue layer. If your images are well-aligned, the image appears normal. If you see areas thatare dominantly yellow or blue, this indicates poor registration.

2. Check the Smoothing check box.

3. Click the Zoom Box Tool button on the Standard toolbar.

4. Drag a zoom box over a very small area of the image that contains land and water.

Errors in registration appear as either blue or yellow pixels because this is where the twoimages do not align perfectly. This is a very simple way to evaluate the registration of twoimages. If the RMS errors of your GCPs were generally less than one, you should not seemore that one pixel offsets or registration errors.


20 de 27 23/06/2013 14:10

Closing all Windows and Dialogs

To close the image window and Algorithm dialog, follow these steps:

1. Click the Close button in the upper-right corner of the image window.

The window closes and disappears from the screen.

2. Click Close to close the Algorithm dialog.

Only the ER Mapper main menu is now open.

In this exercise, you learn how to use ER Mapper’s Geocoding wizard to orthorectify an airphotousing Exterior Orientation parameters. You orthorectify the same image as in the previousexercise. This time, instead of using ground control points, you enter Exterior Orientationparameters which have been obtained from a photogrammetry, aerial triangulation, orgeoposition system external to ER Mapper.

In the previous exercise, you saved orthorectification parameters in theSan_Diego_Airphoto_34_not_rectified.ers file. This means that you do not have to re-enterthem in this exercise.

Opening the Geocoding Wizard

To open the Geocoding wizard, follow these steps:

1. Click the Ortho and Geocoding Wizard button on the Common Functions toolbar.

The Geocoding wizard opens with the Start tab selected.

2. Click the Load Algorithm or Dataset button for the Input File field to open the filechooser.






8. Double-click the San_Diego_Airphoto_34_not_rectified.ers image to select it.

Note: This is the same file you used in the previous exercise.

9. Click the Orthorectify Using Exterior Orientation button.


21 de 27 23/06/2013 14:10

Note: In this example, you enter exterior orientation parameters that provide information onthe position of the platform or aircraft.

10. Click the Ortho Setup tab.

The fields on the Ortho Setup page should contain the information that you entered in theprevious exercise because it was saved to the header file of the image being orthorectified.

11. Click the Fiducial Point Edit tab.

The fields in the Fiducial Point Edit page should also contain the information you entered inthe previous exercise.

Entering Exterior Orientation Parameters

Exterior Orientation parameters contain information on the position of the platform or aircraft atthe time the image was taken. You must obtain this data from a system external to ER Mapper.If these parameters are not available, you can use ground control points as in the previousexercise.


22 de 27 23/06/2013 14:10

To enter exterior orientation parameters, follow these steps:

1. Click the Exterior Orientation Setup tab.

2. Enter the information in the relevant fields as shown in the table below:

Field Name Description Enter Value

AttitudeOmega

The tilt angle (roll) of the aircraft; which is therotation about the X axis (direction of travel).

0.024233136466399

Attitude PhiThe swing angle (pitch) of the aircraft; which isthe rotation about the Y axis.

0.028555797949162

AttitudeKappa

The azimuth angle (yaw) of the aircraft; whichis the rotation about the Z axis.

0.0019776681959326

ExposureCenter X

The X coordinate of the exposure center of theimage.

483681.44788264

ExposureCenter Y

The Y coordinate of the exposure center of theimage.

3621463.0778646

ExposureCenter Z

The Z coordinate of the exposure center of theimage.

3182.9321414632

ScaleThe scale of the image expressed as adecimal value.

0.000048745007960398

3. Click the Change button to open the ER Mapper Coordinate System Chooser dialog.

4. Select the coordinate system as shown below.


23 de 27 23/06/2013 14:10

NAD27 / UTM Zone 11N is the coordinate system.

Rectifying Images

To rectify the image, follow these steps:

1. Click the Rectify tab.

2. Click the file chooser button in the Output Info section.





7. Type a name for the file in the Save As field using your initials at the beginning, and thenclick OK. For example, type:

JL_Airphoto_orthorectified_advanced

8. Click the Edit Extents button to open the Geocode Output Extents dialog.

This dialog lets you specify how much of the orthorectified image you want to save. Youhave three main options:

• Maximum Extents – Saves the whole image including any portion not visible in thecurrently active image window.


24 de 27 23/06/2013 14:10

• Optimum Extents – Automatically calculates the extents of airphotos to exclude theblack edges around them.

• Custom Extents – Allows you to specify the top-left and bottom-right coordinates of thearea to be included. If you click the Snapshot button ER Mapper automatically selectsthe extents of the visible part of the image in the currently active image window.

9. Select the Optimum Extents button to remove the black edges.


11. Select Nearest Neighbor from the Resampling drop-down list.

Note: The Cell Attributes section also lets you resample the output image to a different cellsize (output cell width and height), and specify a null cell value.

12. Click the Save button to save the orthorectification parameters in theSan_Diego_Airphoto_34 _not_rectified.ers header file.

13. Check the Display Rectified Image check box to display the image after it is rectified.

14. Click the Save File and Start Rectification button.

ER Mapper opens a status dialog to indicate the progress of the rectification.

15. Click OK when the operation finishes.

16. Click Close to exit the Geocoding wizard.

You have rectified the uncorrected airphoto image to correspond to the 1927 North AmericanDatum (NAD27) and UTM zone 11 (NUTM11) map projection.

Note: Do not close the image window with the orthorectified image.

Evaluating Image Orthorectification

To evaluate the image orthorectification, follow these steps:

1. Click the Edit Algorithm button on the Common Functions toolbar to open theAlgorithm dialog.

The Red, Green, and Blue layers of the orthorectified image <yourinitials>_Airphoto_orthorectified_advanced display.

2. Click the Blue Layer to select it.

3. Click the Load Dataset button in the process diagram.






9. Click the San_Diego_Airphoto_34 _rectified.ers image to select it.


25 de 27 23/06/2013 14:10

10. Click the OK this Layer Only button to load it into the Blue layer.

Note: The Red and Green layers should still have the <yourinitials>_Airphoto_orthorectified_advanced image.

11. Select B3:Blue from the band selection drop-down list for the Blue layer.

Displaying Images to Evaluate Registration

To display the two images to evaluate registration, follow these steps:

1. Click the Refresh Image with 99% Clip on Limits button in the Algorithm dialog.

This image combines two different images: one in the Red and Green layers and one in theBlue layer. If your images are well-aligned the image appears normal. If you see areas thatare dominantly yellow or blue, this indicates poor registration.

2. Check the Smoothing check box.

3. Click the Zoom Box Tool button on the Standard toolbar.

4. Drag a zoom box over a very small area of the image that contains land and water.

Errors in registration appear as either blue or yellow pixels because this is where the twoimages do not align perfectly. This is a very simple way to evaluate the registration of twoimages. If the RMS errors of your GCPs were generally less than one, you should not seemore than one pixel offset or registration errors.

Closing all Windows and Dialogs

To close the image window and Algorithm dialog, follow these steps:

1. Click the Close button in the upper-right corner of the image window.

The window closes and disappears from the screen.

2. Click Close to close the Algorithm dialog.

Only the ER Mapper main menu is now open.

After completing the exercises, you know how to perform these tasks in ER Mapper:

• Use the Camera wizard to create a camera file

• Select fiducial markers on an airphoto image

• Use options to modify the GCP display and edit GCPs

• Enter Exterior Orientation parameters for advanced orthorectification

• Use the Geocoding wizard to orthorectify a raw airphoto image to the chosen datum and mapprojection


26 de 27 23/06/2013 14:10

Copyright © 1982 - 2012Intergraph CorporationP.O. Box 240000Huntsville, AL 35813 USA


27 de 27 23/06/2013 14:10

Documents

Image Orthorectification