Lab 7-Photogrammetry

Background: 

The focus of this lab was to understand photogrammetry and to practice performing  photogrammetric tasks on images. More specifically, this lab focuses on understanding the calculations behind photographic scale, understanding stereoscopy and performing orthorectification

 Methods

Part 1:
The first section of the lab focused on understanding photographic scale. Using various equations, I calculated the scale for two aerial images of Eau Claire county. For the first image I was given the ground distance and measured the photo distance on my screen using a ruler. The scale was then calculated using the equation in figure one below

Figure 1:
Equation where S=Scale, pd= photo distance and gd=ground distance

For the second image, I was given the focal length of the camera, the elevation of the camera above sea level and the elevation of the terrain in the image. The scale was calculated using the equation seen below in figure 2,

Figure 2
Equation where S=Scale, f=focal length, H= Altitude above Sea level and h =terrain elevation

This section of the lab also focused on calculating relief displacement in tall objects. Relief displacement was calculated using an image showing a large smokestack on the UWEC campus. I was given the altitude of the sensor and measured the real world height of the smokestack on the image using a ruler. The radial distance, or distance of the object from the principal point, was also measured. Relief displacement was calculated using the equation seen below in figure 3

Figure 3
Relief Displacement Equation where d= displacement, h= real world object height,
r= radial distance and H=camera height above local datum.

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Part 2:

The second part of this lab focused on stereoscopy, or in other terms creating 3-D or stereoscopic images. A stereoscopic image is an image that has been generated using some elevation model. For this assignment we generated two stereoscopic images using a Digital Elevation Model (DEM) and a Digital Surface Model (DSM) created from LiDar data. These images may be seen in the results section of this report. 

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Part 3: 

The third and most in depth section of this lab focused on the process of orthorectification. This is a process that simultaneously removes positional and elevation errors from aerial or satellite images. Using the Imagine Photogrammetry Suite I placed ground control points to orthorectify two images showing an area around Palm Springs. These images were then orthorectified and an orthoimage was created. The results from this process may be seen in the results section of this report
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Results:

Anaglyph images.

Figure 4
Anaglyph image generated using a 10 meter spatial resolution DEM

Figure 5
Anaglyph image generated using a 2 meter Lidar DSM

Out of the two Anaglyph images generated, the second one is a better quality image. This can be attributed to the smaller spatial resolution which results in much more detail in the image.

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Figure 6-
 Ortho-Block project in Photogrammetry Suite

Figure 7
Final Ortho Images

The ortho images generated using orthorectification appear to be accurate from a distance. Overall, the results are acceptable, however when zoomed in some displacement can be seen.

Figure 8
Displacement between the two images.