Lab 6: Geometric Correction

Goal:

The purpose of this lab is to gain experience with different remote sensing concepts and georeference a raster image of the Chicago Metropolitan Statistical Area and Sierra Leone.

Methodology:

Part 1:

I began by adding two images to two separate views in ERDAS imagine. I then used a polynomial equation in the software to geometrically correct the image. To do so I first had to delete the current ground control points of the image. I then added four ground control points. There are certain parameters to follow when choosing these points. First, it needs to be something that is non-changing and has a defined start and end point. Often the curb on a corner or the corner of a roof are good locations. Natural things such as river connections are not good because they can change over time.  Secondly, it is good to have them along the outer edges of the image and scattered.

Once finished, I then calculated the root mean square (RMS) error. This tells me how accurate the georeferenced image is. At first the RMS was very high. I then zoomed into the points and made them more exact on both images until the RMS was less than 2 (Figure 1).

      Figure 1 Screenshot showing a RMS of 0.0002 

Part 2:

For this section I added two images of Sierra Leone. I will be rectifying one of them and the other is used as a reference. I followed the same methods as in part one to fix the images coordinate system. I set the GCPs and then calculated the RMS. I then moved the GCPs to a more accurate location on both images until the RMS was below .1. My RMS is seen below.

Figure 2 Screen shot showing an RMs of less than .1

 Results:

These are the following fixed images created through geometric correction. Figure 3 was created with a nearest neighbor resampling method. While figure 4 used a bilinear resampling method.

Figure 3 part I final image

figure 4 part II final image

Conclusion:

This lab helped me gain experience created a referenced image with the use of geometric correction techniques. It also helped me understand the various methods and techniques that can be used during this process and helped to understand some of the reasons behind each one.

References:

Satellite images are from Earth Resources Observation and Science Center, United States

Geological Survey

Digital raster graphic (DRG) is from Illinois Geospatial Data Clearing House.