Photogrammetry
Goal
This lab introduced students to photographic scale and how to calculate scale when various photographic measurements are available. The lab also introduced basic concepts of photogrammetry, relief displacement and orthorectification.
Methodology
Scale
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| Figure 1: Western Eau Claire, Wisconsin |
The ground distance between points A and points B (Figure 1) is 8,822.47 ft. Students measured the distance between points A and B on the JPEG photograph using a ruler to determine the scale of the photograph.
Ground Distance = 8,822.47 ft.
Measured Distance = 2.1 inches
8,822.47/2.1 = 4201.2
Scale: 1 inch = 4201.2 ft
Students also calculated the scale using focal length, focal height and terrain elevation. The focal height of the photograph was 20,000 ft above sea level and the focal length was 152 feet.
152mm/20,000 ft – 796 ft
152mm/19,204 ft = 1mm/ x ft
Scale: 1 mm = 126.34 ft
Relief Displacement
Students determined the relief displacement of the smoke stack identified by the letter ‘A’ in Figure 2. The height of the camera was 3,980 ft and the scale of the photograph was 1:3,209. To calculate the relief displacement, students measured the height of the smoke stack with a ruler to find its real world height. The radial distance between the principle points of the photograph and the top of the smoke stack was also measured.
Stereoscopy
An anaglyph image was created in this lab to show a 3D perspective view of the City of Eau Claire, Wisconsin. A digital elevation model was added to an aerial image using the Terrain-Anaglyph tool in ERDAS Imagine 2013. The vertical dimension of the image was exaggerating by 2 using this tool.
Elevation features of the city can be seen in the resulting image using Polaroid glasses (Figure 3).
Orthorectification
Students performed orthorectification using ERDAS Image Lecia Photogrammetric Suite (LPS) for SPOT satellite images of Palm Springs, California. The process of orthorectification is used to create a planimetrically true orthoimage. Before an image can be orthorectified, ground control points must be collected to geometrically correct the image. Once the image has been corrected, a panchromatic image is added to the block file and more ground control points are collected. The number of GCPs collected for each image in this lab was 12. 12 Verticle Reference points were collected for the panchromatic image (Figure 4).
The next step was to perform automatic tie point collection to triangulate the images. Figure 5 displays the triangulation report including the RMSE value of the ground control points.
Students determined the relief displacement of the smoke stack identified by the letter ‘A’ in Figure 2. The height of the camera was 3,980 ft and the scale of the photograph was 1:3,209. To calculate the relief displacement, students measured the height of the smoke stack with a ruler to find its real world height. The radial distance between the principle points of the photograph and the top of the smoke stack was also measured.
Radial
Distance = 11 in
Tower Height
= 1 in
D = (3,209 x
11)/3,980 ft
Relief Displacement: 8.87 in
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Figure 2: Eau Claire, WI
Relief Displacement of smoke stack
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An anaglyph image was created in this lab to show a 3D perspective view of the City of Eau Claire, Wisconsin. A digital elevation model was added to an aerial image using the Terrain-Anaglyph tool in ERDAS Imagine 2013. The vertical dimension of the image was exaggerating by 2 using this tool.
Elevation features of the city can be seen in the resulting image using Polaroid glasses (Figure 3).
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| Figure 3: Anaglyph Image of Eau Claire, Wisconsin |
Orthorectification
Students performed orthorectification using ERDAS Image Lecia Photogrammetric Suite (LPS) for SPOT satellite images of Palm Springs, California. The process of orthorectification is used to create a planimetrically true orthoimage. Before an image can be orthorectified, ground control points must be collected to geometrically correct the image. Once the image has been corrected, a panchromatic image is added to the block file and more ground control points are collected. The number of GCPs collected for each image in this lab was 12. 12 Verticle Reference points were collected for the panchromatic image (Figure 4).
The next step was to perform automatic tie point collection to triangulate the images. Figure 5 displays the triangulation report including the RMSE value of the ground control points.
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| Figure 4: GCPS & Verticle Reference Points Collected for Orthorectification & Triangulation |
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| Figure 5: Triangulation Report |
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