Lab 7
Goal and Background
The objective for Lab 7 is to offer an understanding and a practice of important photogrammetric tasks on aerial photographs and satellite images. Certain tasks include calculating photographic scales, measuring the areas and perimeters of features, and calculating relief displacement. Lastly, concepts such as stereoscopy and orthorectification will be introduced and implemented with aerial photographs and satellite images.
Methods
Lab 7 began with viewing a JPEG of an aerial photograph of the western part of Eau Claire county, which showed a portion of Interstate 94. Measuring the segment AB on the screen, the photo distance is approximately 2.5 inches. The true ground distance of that distance is 8822.47 feet. To calculate the scale of the image, divide the photo distance from the ground distance (S = PD/GD). The image's scale is approximately 1":42,347".
The second image of eastern Eau Claire was taken by a high altitude reconnaissance conducted by the National Agriculture Imagery Program in 2005. The camera focal length is 152 mm (f). The photograph was taken at an altitude of 20,000 feet (H) and the elevation of Eau Claire county is 796 feet (h). Calculating the scale using the formula S=f/(H-h), the scale if the image is approximately 1":38,509".
Next, open a image of western Eau Claire county from the NAIP 2005 folder and display it in Erdas Imagine. Use the Measure tool in Home tab to open up the Measurement tab. Click Show Panel where the measurements will be displayed. Click the Polyline drop down and select Polygon. Digitize the parameter of the lagoon on the left side of the image. Double click to finish digitizing and the panel will read the area of the lagoon. Select Polyline in the Polyline drop down and digitize the lagoon again. When finished, the panel will read the parameter of the lagoon.
Open the JPEG of the western part of Eau Claire county from the NAIP 2005 folder. The photo was taken 3,980 feet above the datum (H). In order to calculate the relief displacement of the smoke stack, measure the height of the smokestack using a ruler and multiply that by 3209 given by the image's scale. The product is the height of the smoke stake (h). Next, measure the top of the smoke stake to the Principle Point of the image (r). Use these measurements for the formula d = (h x r)/H. The relief displacement of the smoke stake is approximately +0.22".
In Erdas Imagine, open two viewers and display two photos of Eau Claire at 1 m spatial resolution, each at a slightly different frame of reference. Sync both views and evaluate which picture contains the relief displacement. Obtain a pair of polaroid glasses. Next, replace the Eau Claire city and other jurisdictions image with a DEM of the City of Eau Claire at 10 m spatial reolution. From the Terrain tab, click of Anaglyph to open the Anaglyph Generation window. Set the Eau Claire DEM as the Input DEM and set the City of Eau Claire image as the Input Image. Set the put to a personal folder. Make sure the vertical exaggeration is set to 1 and run the model. Display the output and view it with the polaroid glasses (Figure 1).
Next, open two viewers in Erdas Imagine and display the City of Eau Claire with jurisdictions at 1 m spatial resolution image and the Eau Claire DEM at 2 m spatial resolution. Open the Anaglyph Generation window and run the model with these new images. Display the output and view it with the polaroid glasses (Figure 2).
The last part of Lab 7 deals with orthorectification. In Erdas Imagine, bring in the two Palm Springs, California panchromatic images from the Orthorectification folder into the same viewer. Notice how the two images have some spatial problems. Remove the images and open the IMAGINE Photogrammetry window from the Toolbox tab which opens the LPS Project Manager. Click Create New Block File to open its dialog box. Navigate to a personal folder for the orthorecification output. The Model Setup dialog will then open and choose a Polynomial-based Pushbroom and SPOT Pushbroom as the Geometric Model Category. Then the Block Property Setup dialog will open and click the Set button in the Horizontal Reference Coordinate System section, which will then open the Projection Choose dialog. Set Projection Type to UTM, Spheroid Name to Clarke 1866, Datum Name to NAD27(CONUS), UTM Zone to 11, and North or South Field to North. Units should be in meters. There is no need to change the Vertical information. Click OK to close the dialog.
Next, add imagery to the Block and define the sensor model. To begin, highlight the Images folder under the Block Project Tree View within the IMAGINE Photogrammetry Project Manager window. Then select the Add Frame Icon and select the first SPOT panchromatic image of Palm Springs. Click Show and Edit Frame Properties icon to open the SPOT Pushbroom Frame Editor dialog. Click Edit and confirm the Sensor properties are correct. Selecting OK confirms that the properties are correct and the INT. column in the Manger window turns green because a sensor has been specified for the image.
Now it's time to activate it Point Measurement tool and collect GCPs. Select the Start Point Measurement Tool icon and then the Classic Point Measurement Tool. In the Point Measurement Tool Palette, select Reset Horizontal Reference Source, which opens the GCP Reference Source dialog. Check Image Layer because an existing orthorectified image will be used to collect horizontal GCPs. After clicking OK, the Reference Image Layer dialog opens where the orthorecified image of Palm Springs will be selected. In the Point Measurement Tool, check Use Viewer As Reference, which will bring in the orthorectified image into the left side of the tool window.
To begin to collect horizontal GCPs, click Add and a row for the first GCP will appear in the Reference Cell Array. Select Create Point and plot a GCP on the reference image. Select Create Point again and plot a GCP 1 in its corresponding place in the SPOT image. The placement of the GCP in the refernce image is in a coordinate system and the SPOT image GCP is in a pixel coordinate system. Repeat the steps to plot the second GCP. Afterwards, select Automatic (x,y) Drive. This will let the Manager approximate the placement of the GCP in the SPOT image after the placement of a GCP in the reference image. Plot GCPs 3 through 9.
The next two GCPs will be called Point ID 11 and PointID 12 so they'll be easier to distinguish in the array as they be collected from a different horizontal reference source. Select Reset Horizontal Reference Source from the Tool Pallete. This will also be an Image Layer, then select the second orthorectified image from the Reference Image Layer dialog. The new image replaces the previous one. Add a new point row and rename its ID 11. Plot the tenth (ID 11) GCP on the reference image. Add a new row and call it PointID 12. Plot the next GCP.
Uncheck Use Viewer As Reference. Now select Reset Vertical Reference Source. The Vertical Reference Source dialog opens. Specify DEM and Find DEM. Select the Palm Springs DEM in the Add DEM File Name dialog. This is to collect elevation information for the horizontal GCPs that were just collected. In the Reference Cell Array, select all points. Click Update Z Values on Selected Points. All the Z values are recorded in the Reference Cell Array, taken from the DEM. Select None in the Point # column.
Next, set the Type and Usage. Left click the Type column and select Formula to open its dialog. In the Formula box, type Full and click Apply. This changes all the GCP points to a Full type. Do the same for the Usage column, changing them to Control. Save the work and close out of the Point Measurement Tool.
In the LPS Manager, click Add Frame and select the SPOT panchromatic B image of Palm Springs. Go to Frame Properties to confirm the sensor information. Then, open the Point Measurement Tool again, this time, it's displaying the first panchromatic image along side the second panchromatic image. In the Reference Cell Array, select PointID 1. Point 1 is then shown in the first panchromatic image where it was placed. Find its corresponding point in the panchromatic B image and plot a point. Do the same for points 2, 5, 6, 8, 9, and 12. The GCPs not mentioned don't have their corresponding locations in the panchromatic B image. Select None in the Point # column, and save the work.
Next, collect tie points. To do this, click Automatic Tie Point Generation Properties from the palette, which opens its dialog. For Images Used, select All Available. Set Initial Type to Exterior/Header/GCP. Confirm the the Image Layer Used for Computation is set to 1. In the Distribution tab, set the Intended Number of Points/Images to 40. Keep All Point unchecked and run it. Tie points are then automatically generated, their Type being None and Usage being Tie. Read the Auto Tie Summary and close the window. Check the tie point for accuracy and inactivate any that are poor. Save and close the tool window.
With GCP and tie points, triangulation is possible. Click Edit < Triangulation Properties. In the Triangulation dialog, change the Iterations With Relaxation to 3. Confirm that the Image Coordinate Units for Report is set to Pixels. In the Point tab, select Same Weighted Values for the Ground Point Type and Standard Deviations Type. Change the X, Y, and Z values to 15 because the first reference image spatial resolution was 20 meters. 15 will ensure that the GCPs are accurate to approximately 15 meters. In the Advanced Options tab, verify that the Simple Gross Error Check Using box is checked and the default value of Times of Unit Weight is 3. Run the triangulation. The Triangulation Summary Report open. Click report and save the report as a ASCII Text File to a personal folder. Review the information and close the report. Accept the Triangulation Summary and click OK. According to LPS Manager, not the exterior orientation information has been supplied. Save the block.
Now, it's time to create the orthorectified images. Select Ortho Resampling Process in the LPS Manager. In the Ortho Resampling dialog, click the DTM source drop down list an select DEM. for DEM File Name, choose Find DEM and input the Palm Springs DEM. Set the Output Cell Sizes for X and Y to 10. Save the output to a personal folder. In the Advanced tab, confirm that the Resampling Method is Bilinear Interpolation. Click Add which will open the Add Single Output dialog. Make sure that the Input File Na,e is the panchromatic B image and check Use Current Cell Sizes. Click OK to close the dialog. Both SPOT panchromatic images have been added to the Ortho Resampling dialog with the same parameters. Click OK to run the model. View the images in the same viewer in Erdas Imagine (Figure 3).
The last part of Lab 7 deals with orthorectification. In Erdas Imagine, bring in the two Palm Springs, California panchromatic images from the Orthorectification folder into the same viewer. Notice how the two images have some spatial problems. Remove the images and open the IMAGINE Photogrammetry window from the Toolbox tab which opens the LPS Project Manager. Click Create New Block File to open its dialog box. Navigate to a personal folder for the orthorecification output. The Model Setup dialog will then open and choose a Polynomial-based Pushbroom and SPOT Pushbroom as the Geometric Model Category. Then the Block Property Setup dialog will open and click the Set button in the Horizontal Reference Coordinate System section, which will then open the Projection Choose dialog. Set Projection Type to UTM, Spheroid Name to Clarke 1866, Datum Name to NAD27(CONUS), UTM Zone to 11, and North or South Field to North. Units should be in meters. There is no need to change the Vertical information. Click OK to close the dialog.
Next, add imagery to the Block and define the sensor model. To begin, highlight the Images folder under the Block Project Tree View within the IMAGINE Photogrammetry Project Manager window. Then select the Add Frame Icon and select the first SPOT panchromatic image of Palm Springs. Click Show and Edit Frame Properties icon to open the SPOT Pushbroom Frame Editor dialog. Click Edit and confirm the Sensor properties are correct. Selecting OK confirms that the properties are correct and the INT. column in the Manger window turns green because a sensor has been specified for the image.
Now it's time to activate it Point Measurement tool and collect GCPs. Select the Start Point Measurement Tool icon and then the Classic Point Measurement Tool. In the Point Measurement Tool Palette, select Reset Horizontal Reference Source, which opens the GCP Reference Source dialog. Check Image Layer because an existing orthorectified image will be used to collect horizontal GCPs. After clicking OK, the Reference Image Layer dialog opens where the orthorecified image of Palm Springs will be selected. In the Point Measurement Tool, check Use Viewer As Reference, which will bring in the orthorectified image into the left side of the tool window.
To begin to collect horizontal GCPs, click Add and a row for the first GCP will appear in the Reference Cell Array. Select Create Point and plot a GCP on the reference image. Select Create Point again and plot a GCP 1 in its corresponding place in the SPOT image. The placement of the GCP in the refernce image is in a coordinate system and the SPOT image GCP is in a pixel coordinate system. Repeat the steps to plot the second GCP. Afterwards, select Automatic (x,y) Drive. This will let the Manager approximate the placement of the GCP in the SPOT image after the placement of a GCP in the reference image. Plot GCPs 3 through 9.
The next two GCPs will be called Point ID 11 and PointID 12 so they'll be easier to distinguish in the array as they be collected from a different horizontal reference source. Select Reset Horizontal Reference Source from the Tool Pallete. This will also be an Image Layer, then select the second orthorectified image from the Reference Image Layer dialog. The new image replaces the previous one. Add a new point row and rename its ID 11. Plot the tenth (ID 11) GCP on the reference image. Add a new row and call it PointID 12. Plot the next GCP.
Uncheck Use Viewer As Reference. Now select Reset Vertical Reference Source. The Vertical Reference Source dialog opens. Specify DEM and Find DEM. Select the Palm Springs DEM in the Add DEM File Name dialog. This is to collect elevation information for the horizontal GCPs that were just collected. In the Reference Cell Array, select all points. Click Update Z Values on Selected Points. All the Z values are recorded in the Reference Cell Array, taken from the DEM. Select None in the Point # column.
Next, set the Type and Usage. Left click the Type column and select Formula to open its dialog. In the Formula box, type Full and click Apply. This changes all the GCP points to a Full type. Do the same for the Usage column, changing them to Control. Save the work and close out of the Point Measurement Tool.
In the LPS Manager, click Add Frame and select the SPOT panchromatic B image of Palm Springs. Go to Frame Properties to confirm the sensor information. Then, open the Point Measurement Tool again, this time, it's displaying the first panchromatic image along side the second panchromatic image. In the Reference Cell Array, select PointID 1. Point 1 is then shown in the first panchromatic image where it was placed. Find its corresponding point in the panchromatic B image and plot a point. Do the same for points 2, 5, 6, 8, 9, and 12. The GCPs not mentioned don't have their corresponding locations in the panchromatic B image. Select None in the Point # column, and save the work.
Next, collect tie points. To do this, click Automatic Tie Point Generation Properties from the palette, which opens its dialog. For Images Used, select All Available. Set Initial Type to Exterior/Header/GCP. Confirm the the Image Layer Used for Computation is set to 1. In the Distribution tab, set the Intended Number of Points/Images to 40. Keep All Point unchecked and run it. Tie points are then automatically generated, their Type being None and Usage being Tie. Read the Auto Tie Summary and close the window. Check the tie point for accuracy and inactivate any that are poor. Save and close the tool window.
With GCP and tie points, triangulation is possible. Click Edit < Triangulation Properties. In the Triangulation dialog, change the Iterations With Relaxation to 3. Confirm that the Image Coordinate Units for Report is set to Pixels. In the Point tab, select Same Weighted Values for the Ground Point Type and Standard Deviations Type. Change the X, Y, and Z values to 15 because the first reference image spatial resolution was 20 meters. 15 will ensure that the GCPs are accurate to approximately 15 meters. In the Advanced Options tab, verify that the Simple Gross Error Check Using box is checked and the default value of Times of Unit Weight is 3. Run the triangulation. The Triangulation Summary Report open. Click report and save the report as a ASCII Text File to a personal folder. Review the information and close the report. Accept the Triangulation Summary and click OK. According to LPS Manager, not the exterior orientation information has been supplied. Save the block.
Now, it's time to create the orthorectified images. Select Ortho Resampling Process in the LPS Manager. In the Ortho Resampling dialog, click the DTM source drop down list an select DEM. for DEM File Name, choose Find DEM and input the Palm Springs DEM. Set the Output Cell Sizes for X and Y to 10. Save the output to a personal folder. In the Advanced tab, confirm that the Resampling Method is Bilinear Interpolation. Click Add which will open the Add Single Output dialog. Make sure that the Input File Na,e is the panchromatic B image and check Use Current Cell Sizes. Click OK to close the dialog. Both SPOT panchromatic images have been added to the Ortho Resampling dialog with the same parameters. Click OK to run the model. View the images in the same viewer in Erdas Imagine (Figure 3).
Results
The first anaglyph image of Eau Claire wasn't very accurate (Figure 1). Using the polaroid glasses, none of the buildings showed any elevation. Only forested areas showed elevation while everything else remain flat. This might be because the image used had high levels of relief displacement and had a spatial resolution of 2 meter, while the DEM has a spatial resolution of 10 meters.
Figure 1: The first anaglyph image of Eau Claire.
The second anaglyph was more accurate than the first one (Figure 2). Tall building as well as forested areas displayed elevation with the polaroid glasses. This might be because the image used had minimal relief displacement and its spatial resolution was 1 meter, while the DEM used had a spatial resolution of 2 meters. This isn't nearly as extreme of a difference than the first anaglyph.
Figure 2: The second anaglyph image of Eau Claire.
The orthorectified images of the two panchromatic SPOT images in the same viewer create a near seamless boundary at the spatial overlap. Orthorectified images have planimetric accuracy, which have minimal positional and elevation errors.
Figure 3: Both orthorectified images of the Palm Springs panchromatic SPOT satellite images.
Sources
National Agriculture Imagery Program (NAIP) (2005). Satellite Images. United States Department of Agriculture.
Digital Elevation Model (DEM) (2010). Eau Claire, WI DEM. United Stated Department of Agriculture Natural Resources Conservation Service.
Li-DAR-Derived Model. (n.d.) Eau Claire DSM. Eau Claire County.
Li-DAR-Derived Model. (n.d.) Chippewa DSM. Chippewa County.
SPOT Satellite. (2009) Spot Satellite Images. Erdas Imagine.
Digital Elevation Model (DEM) (2009). Palm, Springs, CA. Erdas Imagine.
National Aerial Photography Program (NAPP) (2009). 2 meter images. Erdas Imagine.
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