Lab 7

Introduction:

The main goal of this laboratory exercise is to develop my skills in performing key photogrammetric tasks on aerial photographs and satellite images. Specifically the lab is designed to train me 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 me to stereoscopy and performing orthorectification on satellite images. At the end of this lab exercise, I will be in a position to perform diverse photogrammetric tasks.

Methods:

                The lab was broken up into three parts. Part one had us calculating scales, measurements, and relief displacement.  We had to calculate the scale of an image by only being given two points on the image and the distance between them. To do this we had to take that distance and the distance on the screen as measured by a ruler and run an equation to find the representative scale. Another image that we had to calculate the scale for was where we were only given the altitude of the aircraft that took the photo, the focal length of the lens, and the elevation of Eau Claire. This was simple division after we converted everything to inches.  We were also introduced to the measurement tools in Erdas and some different ways we can calculate area and perimeter.

                The second part of the lab was creating a stereoscopic images in Erdas. This was very interesting and to complete the task we needed an image and a DEM of that image. The result of the tool we ran was an anaglyph image. The process of making that anaglyph image was just entering the files into the tool and running it. By using polaroid glasses we could view the image as if it was in 3D.

                The final and longest part of the lab was orthoreticifying two images together in Erdas to be used for triangulation and other analysis that requires two images. The roots of the tool that we ran (which is called LPS or Lecia Photogrammetric Suite) is setting it up for the two images that we will input. We had to verify that the images were collected in a polynomial based SPOT pushbroom technique to help figure out the geometry of the tool. Then we added the correct coordinate systems for the images and then began the select point measurement tool. In this tool we have our two different images next to each other with different views of the images that get more and more detailed. We simply had to place one Ground Control Point (GCP) on the first image and then find the same location so that we could place it on the second image. After placing two GCPs we were able to Automatically drive the x,y coordinates from the first image to the second. As we kept adding points, the automatic point generation got closer and more accurate to the first image. We started just entering in the coordinates for the first image and then having the next point driven to the second image of where we verified where the point was.

                The next step was to set the vertical reference source by using a DEM file for Palm Springs. It was the same technique as used in the first step but this time it also updated the Z elevation for the image. This process was very quick and led into the next step which was automatically tieing points together and resampling the triangulation and ortho images. This consisted of many adjustments made to the output images that we were about to create and after they were finished processing we were able to bring them back into an Erdas viewer to see how accurate the images were rectified together.

Results:

Anaglyph image that can be seen in 3D when using polaroid lenses, can you see it?

Final Orthorectification image pair that I created.

 

Summary:

                This lab consisted of many valuable tools that we learned from finding the scale of an image and how to measure it, to making our own 3D image, to orthorectifying images together. These tools can be used in a variety of ways for a wide range of potential careers and by having the ability to say that I can  run these image processing tools, I am able to market myself in a very experienced way.

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.