GIS@Grinnell : Training

Terraserver Image Registration

1. Determine area of interest and level of detail required.
2. Log on to Terraserver.
3. Navigate to desired Location using either Image Map or "FIND".
4. Select level of detail using zoom and "Image Size Selection".
   1. The highest level of "Zoom" is equivalent to 1 pixel per meter.
   2. The largest "Image Size" Selection (Large) is 800 x 600 pixels.
5. Select "Image Info" link.
   1. The "Image Info" page includes the image's metadata in text format at the top and a view of the map with georeferencing information at the bottom.
   2. From the metadata record pixel size of image (i.e., 400 x 200).
   3. From the metadata record projected coordinate system (i.e., UTM NAD 1927 Zone 12N).
   4. From the image record coordinate pairs for upper left and lower right corners of the image (The image includes lat./long. and UTM coordinates. Use whichever you intend to use in your GIS).
6. Download Image.
   1. Left-Click "Download".
   2. Left-Click "Free Download".
   3. Right-Click image, select your browsers equivalent of the "Save Image As" menu item, and save image file (Note: Carefully select your folder and file names).
7. Create Link Table file using a text editor (example):
   1. Use a text editor such as Notepad (do not use a wordprocessor).
   2. Line 1 should simply have the text "link table".
   3. Each subsequent line corresponds to a particular pixel on the image and includes four values separated by tabs.
   4. The four values should correspond to coordinate pairs (X of Image, Y of image, X of geographic coordinate system, and Y of geographic coordinate system).
      1. The first point of the image is 0 [tab] 0 and corresponds to the upper left corner.
      2. The second point of the image corresponds to the lower right (usually something like 400 [tab] -200 or 800 [tab] -400).
   5. NOTE: Do not include carriage returns at the end of the last line.
8. Georeference image:
   1. Load image into ArcMap.
   2. Load Georeferencing Toolbar if it is not already available (On MENU select VIEW -> TOOLBARS -> Georeferencing).
   3. Click on "View Link Table" button on Georeferencing toolbar.
   4. Click on "Load" button in Link Table dialog box (lower left corner of dialog box) and select the Link Table file that was created previously.
   5. Click on "OK" and then pan and zoom to registered image in map.
   6. From the Georeferencing Toolbar select the Georeferencing Drop-Down Box and select Update Georeferencing to permanently associate the new coordinate system with the image.
9. Did it work?
   1. If your image properly aligns with your base data go on to step 10.
   2. If the image does not align properly with your base data, the image is probably using the NAD83 datum and your base data is probably using the NAD27 datum.
   3. The easiest way to fix this problem is to add and subtract values interactively from the X Map and Y Map values in the Link Table Dialog until the image and map data align.
   4. NOTE: Look for a feature visible in both maps and use the Measure tool in the Tools toolbar to estimate the x and y offsets. Remember to change both X Map values the same amount to avoid stretching the image. DO the same with both Y Map values.
10. Permanently associate the new coordinate system with the image.
    1. From the Georeferencing Toolbar select the Georeferencing Drop-Down Box and select Update Georeferencing.