Photogrammetry

Goals:

The purpose of this lab was to develop skills in photogrammetry. The main goals of this lab were to calculate scales, measure areas and perimeters, calculate the amount of relief displacement. Also a focus was to develop skills in stereoscopy and finally orthorectification of satellite images

Methods

Part 1: Scales, Measurements and Relief Displacements 

To be able to calculate the scale of a vertical aerial image we compared the size of objects measured in the real world with the same objects measure on a photograph and used the scale to complete the mathematical equation. We also used an equation finding the relationship between the camera lens focal length and elevation of the aircraft.

We then created a polygon shape around the edge of the lake in order to calculate the water bodies' area and perimeter.

Relief displacement which is the displacement of a part of the image was corrected by applying an equation and reprocessing the image.

Part 2: Stereoscopy

We created  3D images with a digital elevation model. The result was an anaglyph which we were able to further analyze using special polaroid glasses with a red and blue lense.    

We created anaglyph using the function in Terrain in Erdas and compared the two images that we had created.

Part 3: Orthorectification

The next part of the lab used digital photogrammetry for triangulation and the orthorectification of images.  We used the LPS system to orthorectify images. We were able to create a planimetrically true image (Figure 3). We used two orthorectified images for a SPOT image and an orthorectified aerial photo and to collect ground control points (GCPs).  To orthorectificatify these images we would create a new project ad select a horizontal reference source then we would collect GCPs (Figure 2) (Figure 3). We then added an image to block file and collected GCPs from this image as well. We then performed an automatic tie point collection which bound the points from the two photos and triangulated the images. We were then able to orthorectify the images and inspect the image in greater more accurate detail.

Figure. 1 Work screen displaying GCPs and SPOT image

Figure. 2 Display of GCP points from the two images

Results:

Figure. 3 Final orthorectified image

The orthorectified image produced from the method displays a higher degree of spatial accuracy, specfically in the overlaping area of the two photographs.

Sources:

Digital Elevation Model of Eau Claire, WI: U.S. Department of Agriculture Natural Resources Conservation Service, 2010

DSM of areas of Eau Claire and Chippewa: Eau Claire County and Chippewa County government.

Erdas Imagine, 2009.