Lab 7: Photogrammetry

Lab 7: Photogrammetry

 

 

Goal and Background

Lab 7 consists of several main goals. Part 1 is aimed at understanding how to calculate image scales based on altitude of a flight path and the focal length of the camera used to take aerial photographs. Part 1 also looks calculating relief displacement based on height of the object and distance from the principal point of the image. Part 2 of Lab 7 involves creating an 3D anaglyph of Eau Claire, WI. Part 3 uses Erdas Imagine Lecia Photogrammetric Suite to create orthorectified images.

Methods

 Part 1

Using the equation Scale= focal length/altitude of flight path we are able to calculate the scale of the aerial photograph. Given is the focal length is 152mm and the flight path is 19204ft above the land surface we can calculate the scale using simple unit conversions. Next we are able to calculate relife displacement using the equation displacement=(height of the object * radial distance)/flying height of the camera.

Part 2

Part 2 of Lab 7 uses a digital elevation model of an area and combines it with a geometrically correct aerial photograph to create a 3D anaglyph that shows general surface features.  

 

Part 3

 Part 3 of the lab was learning how to use previously orthorectified images to geometrically correct other images from the Palm Springs, CA area. We start by defining the projection of the image to be corrected. Next we collect ground control points on the already geometrically corrected image and the image that needs to be corrected. After collected 10 GCPs we also need to collect GCPs from another geometrically correct orthophoto and a digital elevation model to create elevation coordinates. Next, we use LPS to generate 40 automatic tie points in the images.  Finally, we use triangulation and resampling to create the orthorectified photograph.

 

 

Results

 Part 1

Based on the scale equation above we can calculate that the scale of the Eau Claire_West-se image is 1:38498. We can also conclude, based on the relief displacement equation above, that the relief displacement of the smoke stack located on the UWEC campus has a relief displacement of .35inches on the image.

 

Part 2

Using 3D glasses we are able to distinguish some of the 3D features in the anaglyph of Eau Claire. These features are only noticeable when zoomed in. Figure 1 below shows a zoomed in screenshot of the anaglyph focusing on the UWEC campus area. There is a significant change in elevation in the forrested area that spans horizontally across the image.

Figure 1 3D anaglyph of the UWEC campus area.

Part 3

 Figure 2 below is the final output of the orthorectification of the aerial photo of Palm Springs, CA. The orthophoto has a very high degree of spatial accuracy.

 

 

Figure 2 Orthorectified photo of Palm Springs, CA

Sources

 

National Agriculture Imagery Program (NAIP) images are from

United States Department of Agriculture, 2005.

 

Digital Elevation Model (DEM) for Eau Claire, WI is from United States Department of 

Agriculture Natural Resources Conservation Service, 2010.

 

Spot satellite images are from Erdas Imagine, 2009.

 

Digital elevation model (DEM) for Palm Spring, CA is from Erdas Imagine, 2009.

 

National Aerial Photography Program (NAPP) 2 meter images are from Erdas Imagine, 2009.