Upper Midwest Environmental Sciences Center

DOQ Background Information

Background Information - DOQs

The Upper Midwest Environmental Sciences Center (UMESC) is in the process of compressing and serving U.S. Geological Survey (USGS) digital orthophoto quadrangles (DOQ) images for the Upper Mississippi River System. The files are being compressed using using LizardTech's compression program Multiresolution Seamless Image Database (a.k.a., MrSID).

The original file size of these images is approximately 45 megabytes (mbyte) each. MrSID compresses them to approximately 2 mbytes each, using a lossy compression routine. An image viewer is available. The image viewer is also capable of exporting the compressed images to georeferenced TIFF images (a .tif image and a .tfw world file).

Also available is a new dynamic link library file (.DLL) for the ArcView GIS version 3.1/3.2 MrSID extension program. At the time this Web page was prepared, the .dll file distributed with version 3.1 was outdated. A new .dll file was needed if an individuals running ArcView software wanted to view the images at full resolution.

MrSID compressed DOQs are being served as a result of a CRADA (Cooperative Research And Development Agreement) between the USGS and LizardTech. These compressed DOQs are 1:12,000 (12k) gray scale geometrically corrected and rectified images at a resolution of 1 meter per pixel and conform to National Map Accuracy Standards. Since MrSID is a lossy compression, subtle differences between the original and compressed image may be noticeable at high magnification.

All DOQs served by UMESC are bundled in a self-extracting file that contains the image (*.sid), the world file (*.sdw), and a text file with additional image information (*.wri). Most images have been compressed from their original Band Inteleaved (BIL) format, but a few are compressed JPEGs that were uncompressed, then recompressed using MrSID. This information is reflected in the 'Compression Flag' field of the text file with a 'C' and these images will have slightly less contrast.

All images are referenced in UTM, North American Datum of 1927 and may be used with other UMESC spatial data. The world file is in the following format:

1.000000000000000 (The X dimension of the pixel, which, in this case, is meters.)
0.000000000000000 (Image rotation information)
0.000000000000000 (Image rotation information)
-1.000000000000000 (The Y dimension of the pixel, also in meters)
635425.000000000000000 (X coordinate of upper left corner pixel in UTM, NAD27)
4859461.000000000000000 (Y coordinate of upper left corner pixel in UTM, NAD27)

There are many freeware and shareware coordinates conversion utilities available, including Corpscon, distributed by the U.S. Army Corps of Engineers at http://crunch.tec.army.mil/software/corpscon/corpscon.html.

If you require these data in their original format, contact the EROS Data Center.

Page Last Modified: April 3, 2018