This exercise is designed to introduce image processing methods for geometric restoration for satellite imagery. In other words you will add geographic coordinate information to some satellite imagery. The result is an image which essentially becomes a map, therefore you can use it as such, make measurements and determine areas using real world units. This is particularly important when you want to use the image with other geographic information, such as in any GIS analysis procedures.
In this exercise you will register an area of the Hong Kong Landsat TM image to real world geographic coordinates. The approach we will use involves establishing mathematical relationships between the adresses of pixels in an image and the corresponding coordinates of those points on the ground (image to map registration). To do this we identify Ground Control Points (GCP's), these are points which are clearly identifiable in both the image and on a map. For these points we extract the pixel locations and associated map locations. Then define a mathematical equation which relates the pixel and map coordinates, so that given any pixel coordinate we can use the equation to derive the map coordinate and vice versa. Once the Hong Kong Landsat image has been registered, you will use this to register a high resolution panchromatic image of Hong Kong (image to image registration).
It is assumed that you have already completed the ENVI Tutorial and are therefore, somewhat familiar with the workings of ENVI. You should also have a directory named 'RSData' as a subdirectory of your home directory containing a copy of a Landsat TM image of Hong Kong and its associated header file. If you completed the tutorial all should be in order. If for some reason you need to set up the 'RSData' directory containing the imagery go to download information, otherwise continue on.
Before beginning the exercise you will also need an additional image file. This is a panchromatic image (single band) of Kowloon and Hong Kong Island with a 10 meter resolution. Later you will register this image to real world coordinates using the process of image to image registration.
| You will be prompted for the location to save the image file during the download process. Make sure you specify 'RSData' as the destination directory. Go ahead and click the download icon. |
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The image and its header file have been downloaded to you as a Zipped self extracting executable. In order to use this file you must first Unzip it. This is done by opening your Windows file manager (Windows NT Explorer), navigating to your "RSData" directory and double clicking on the filename. You will be asked where you wish to expand (place) the contents of the Zip file. Make sure you specify your 'RSData' directory as the destination location. Again, using the Windows NT Explorer, check to see if both files were successfully placed. You should have the following files in your 'RSData' directory:
Move on and begin the exercise .....
