Lab 7: Photogrammetry and Orthorectification

Goals and Objectives

The main goal of this laboratory exercise is to develop your skills in performing key photogrammetric tasks on aerial photographs and satellite images. Specifically the lab is designed to train you in understanding the mathematics behind the calculation of photographic scales, measurement of areas and perimeters of features, and calculating relief displacement. Moreover this lab is indented to introduce you to stereoscopy and performing orthorectification on satellite images. At the end of this lab exercise, students will be in a position to perform diverse photogrammetric tasks.

Methods

Photogrammetry 

Four different photogrammetry methods were used to come up different scales and relief displacement.  The first method we were given an aerial image and the actual distance measured.  We had to find the scale by using a ruler and measuring the distance on the aerial image.  The scale was found using this equation: Actual distance Measured/Measured Distance on the Map.  The second method we were given the focal lens length, the height of the aerial flight, and the elevation of the point on the surface.  We calculated the scale by this equation: Focal Lens Length/(Height of Aerial Flight-Elevation Point).  The third method we used was to find the area and perimeter of a lagoon on the Southwest side of Eau Claire.  We had to use the area and perimeter tool in ERDAS.  I digitized the lagoon and the area was given.  It was in hectares and miles.  The perimeter was in meters and miles.  The fourth method used was to calculate the relief displacement when we were given the height of the smoke stack in real life and the height of the camera.  This was calculated by this equation: Height of Object in Reality x Radial Distance from Principal Point to Top of Object / Height of Camera.

Sterescopy

This tool was rather simple to use.  With a DEM given, certain parameters were changed to get the wanted end result.  I had to create a stereoscopic image of the city of Eau Claire.  The end result was an image that displayed the elevation of the City of Eau Claire.

Orthorectification

This was a long, tedious process!  I first had to set ground control points on my images.  I created 12 GCP's.  I then had to assign the image a DEM and another panchromatic image to correct. 

Results

Photogrammetry Results

The image below is the first task of the photogrammetry section of the lab.  I calculated the scale to be 1:38,498.

The image below is the second task in photogrammetry.  I calculated the scale to be 1: 38,509.

The image below is the third task in the photogrammetry section of the lab.  I calculated the area and perimeter of the lagoon in acres, hectares, miles, and meters.

The image below is the last part of the photogrammetry section of the lab.  I had to calculate the relief displacement of the smoke stack.

Stereoscopic Results

The image below is the result of the stereoscopic task.  It is suppose to be almost a 3D image of Eau Claire, but it is hard to see the elevation and relief without 3D glasses on.

Orthorectification Results

The image below is the results of the orthorectification lab section.  Through multiple steps like adding GCP's, importing a DEM, and rectifying the image the image was created.

Conclusion

This was the longest lab of the semester so far for this class.  It took a long time to complete.  Overall, I believe it was a very helpful lab that taught us a lot.  The photogrammetry skills in this lab were very helpful and could be used to get a job.