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A Publication Featuring The Information Services Technology of Maine State Government
|Volume IV, Issue 6||June 2001|
By David Kirouac
What is a DOQ? A DOQ (Digital Orthophoto Quad) is an aerial photograph that has been registered to geographic coordinates so that these "smart" images know where they are in reference to the earth. For more technical information about DOQs you can visit the USGS (U.S. Geological Survey) website at http://mapping.usgs.gov/www/ndop/.
Can you find the State House in this DOQ of the Capitol Complex area?
Click the image for a larger version.
Why are these "smart" images important and how can they be used? By having coordinate information associated with the DOQ, the image can easily be incorporated into a GIS (Geographic Information System) and used in conjunction with other "smart" imagery and GIS data. The Maine Office of GIS is currently using the DOQs to enhance the E911 roads database, the Maine Department of Environmental Protection is using the DOQs for spill response mapping and to quality control other GIS data, and the Maine Department of Marine Resources is using the DOQs to quality control databases of eelgrass beds.
One problem the Maine Office of GIS (MEGIS) encountered with the DOQs is large file sizes. Each DOQ which covers one USGS 7.5 minute quadrangle, is approximately 165MB (megabytes) and there are over 700 quadrangles in Maine. 165MB x 700+ = a major storage and distribution problem! To resolve these problems, MEGIS purchased the MrSid image compression software from Lizardtech, Inc. (http://www.lizardtech.com) to compress the DOQs to a more manageable size. After using the MrSid compression software each 165MB image becomes only 12.5MB!
The Maine Office of GIS will soon be making all of the available DOQs available in MrSid compressed format free from its Internet Data Catalog, http://apollo.ogis.state.me.us/catalog/catalog.asp. The DOQs will also be incorporated into the MEGIS Internet mapping, http://apollo.ogis.state.me.us/mapping/mapframe.htm, so the images can be viewed with an ordinary Internet browser.
Questions? Contact David Kirouac (David.Kirouac@state.me.us). David is a Senior GIS Programmer Analyst at the Maine Office of GIS.