Image Registration Info Available from Terraserver

By Joseph J. Kerski, USGS

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Since mid-1998, Terraserver ( terraserver.microsoft.com) has been serving up millions of images each month from compressed USGS Digital OrthoPhoto Quads (DOQs), Russian SPIN-2 imagery, and more, and recently the USGS topographic maps in digital format (Digital Raster Graphics) and links to the USGS stream gaging stations from these DRGs. The Microsoft TerraServer web site is one of the world's largest online databases, with 20 terabytes of disk storage, allowing anyone to quickly and easily use maps and images to explore the United States and certain places around the world with a standard web browser. An average of 40,000 users request 4,000,000 images from the site everyday. This magnificent site grew out of a cooperative research and development agreement with Microsoft to compress Terrabytes of images using MrSID compression routines. Some images have been available for download and in all cases, for purchase.

The DOQs have been useful in exposing a wide variety of users, mostly non-GIS users, to the power and utility of digital imagery of the landscape. They have not been able to be used in GIS software directly from the Terraserver without the user placing them side-by-side with vector data and usinig registration and rectification algorithms within these software packages... until now.

Yes, that's right! I'm pleased to report that when a user clicks on the "download" button, he or she has the option of downloading a header file! This will allow the user to directly use This header file is a text file and should be saved with a .jgw extension [note that there is an error on the web page that indicates the wrong naming convention] with the base name the same as the image. Therefore, if you download a "blair.jpg" image, you should name the header file "blair.jgw" so that your GIS software will read it.

I tried this recently, downloading an image of Blair, Nebraska. The DOQs, as most USGS data, are in UTM meters. Then I downloaded USGS 100,000-scale digital line graph (DLG) roads data (from http://edcwww.cr.usgs.gov - WebGLIS - soon to be http://earthexplorer.usgs.gov) for the same area and overlaid the two. They were offset as seen on the image attached, terraserveroff_sm.jpg. Why were they offset? The DOQs are cast on the North American Datum (NAD) of 1983 while the 100K DLGs are on NAD 1927. See attached terraserveroff_sm.jpg for a screen shot of the roads in red and the DOQ as well. Note the detail of the DOQ is 2 meters at this scale, but you can, of course, zoom in so that your resulting image is 1 meter resolution.



Thus, there is an offset if you use USGS DLGs and USGS DOQs together. But - no problem! You have several options. One, measure the offset and adjust the header file (in my case, blair.jgw) according to the offset in the x and y directions. I had to add 30 meters easting (x) and subtract 200 meters northing (y) which were the last 2 lines in the header file. A second option is to use the tricon program to give you a conversion between NAD 27 and NAD 83 which you can use to edit your header file, available from the bottom of the page http://rockyweb.cr.usgs.gov/software. A third option is to use your GIS software's register and rectify commands to rubber-sheet your image to an established set of vector features, such as roads. In the case of ArcView, you can use the K12 School Tools extension or the Image Analysis extension.

I used option 1 [adjusting 2 numbers in the header file] and the result is shown in the following image:

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Thanks to Joseph Kerski of the USGS for providing us with this information. All rights reserved. Any copying or reproduction of the article in whole or in part is strictly prohibited.