Lab 6: Geometric Correction

Goal

The name of this lab is "Geometric Correction" and our main goal was to fix the distortion between two maps that are representing the same image and creating a new map with less to no distortion. During this lab we learned a few new skills while doing it, for instance we learned two major types of geometric correction, one was the pre-processing of activities prior to the extraction of the biophysical and sociocultural information from satellite images. In order to complete these tasks and to learn these skill sets, we needed to use Erdas Imagine to help us complete each of the tasks that were represented to us in the lab. 

Methodology/Results 

The first step of the lab was to upload two maps that represented the same location and try to fix the distortion for one of them so than both maps would match exactly. In order to do this we had to upload both maps into Erdas, and than find the control points that were made on the map originally, the points that were causing the distortion in the first place. Once we deleted all of the control points it was our job to make our own and try to get the points to match correctly in each map so than the points would be in the exact same location. Once we created three control points and attempt to match them up every point after that would automatically match up because the polynomial order is at 1 meaning that there only needs to be three points for the points to start matching up by themselves. After we got our four points on their our goal was to get the Root Mean Square (RMS) error down to 2.0 or lower, the lower the RMS was the less distortion we would have in the image. Below is an image of the maps known as figure 1 with the four control points on it and with the RMS lower than 2.0 or is this case at 1.5757.

Figure 1

The next step for the lab was the same objective as the first, compare two images that are representing the same area and try to find and get rid of the distortion by using Erdas Imagine. This time its a little more difficult though because we were asked to change the polynomial order from 1 to 3 which means that we need to use more control points before they automatically get added to the corresponding map. In this case we had to add ten different control points all over the map and try our best to match the points from one map to the other before they would automatically match. After we added the ten control points we were asked to add two more and then try to get the RMS error below 1.0. In order to do this we needed to change the location of almost every single control point ever so slightly so than the RMS would read below 1.0. Below is an image known as figure 2 and this figure represents the two new maps being compared, with 12 control points and with an RMS of 0.7137. 

Figure 2

This lab was very helpful is finding out different ways on Erdas to remove distortion from images or at the very least get rid of some of the distortion. I thought of this lab as a great learning experience, and plan to use all of the skills picked up this lab in the future.