Instructions for Downloading and Processing DOQQ Aerial Photography

Dean Wallraff, Chair, Angeles Chapter GIS Committee deanraff@arsnova.org

For now we're using the free aerial photography available from the US Geological Survey for Angeles Chapter GIS projects. The main reason: it's free! The drawbacks are that it's only medium-resolution, and it doesn't tile together seamlessly -- adjacent images might not match in shading and lighting angle.

The files we can download for free are called DOQQs, which stands for Digital Orthophotograph Quarter Quads. Each is an image of a quarter of a standard 7.5' USGS quadrangle (which is the same area shown on the USGS 7.5' topo maps). The files tend to be about 50Mb in size. We want to have images of full USGS quads in geotiff format in NAD 1927 UTM Zone 11N projection, so we download the four quarter-quads, convert them to geotiffs, stitch them together and reproject them. Here are the details of how to do this:

Got to the following page: http://webclient.alexandria.ucsb.edu/mw/index.jsp. Select "USGS DOQQ" in the "collection to search" field. Type the name of the quad you want (e.g. "long beach") into the "Words to Search For" box toward the bottom of the left hand side of the page. Select "all of the words" then click "start search." You should get back a list containing the 4 parts of the quad you're looking for (NE, NW, SE, SW). The process will be to download the four quarters of the quad and convert each DOQQ to a geotiff, then mosaic the 4 geotiffs together to get a single geotiff that covers the entire quad. Finally the merged geotiff needs to be reprojected from NAD 1983 to NAD1927 (which is the standard for Angeles Chapter GIS files).

For each of the 4 DOQQ files, do the following:

• Click on the "Original DOQQ Imagery" link in the Download section. Save the file somewhere on your computer.
• Open a Command Window (Start, Run, cmd) and cd to the directory where you saved the file in the above step. If you're processing multiple files, open the command window once and leave it open.
• Copy the doq2geotiff.exe program (which converts a DOQQ file to a geotiff) to this same directory. The program is available here in zipped form.
• Run doq2geotiff from the command line with a command like this: doq2geotiff <input file name> <output file name>
  • the <input file name> should be the DOQQ file that you downloaded
  • the <output file name> should be the name of the tiff you want to create. I suggest a name like "sunlandne.tif" for the northeast quarter of the sunland quad

Once you've generated the 4 geotiffs, then mosaic them together and reproject by doing this:

• Open ArcToolbox inside ArcCatalog, double-click on the "Data Management/Raster/Mosaic to New Raster" tool, which will run it. Add the 4 quarter-quads as input, give your output file a name like "sunland.tif" and let 'er rip! This will stitch together the 4 quarter-quads into a single aerial-phtoography quadrangle.
• Now reproject to NAD-27 from NAD-83. Double-click the ArcToolbox "Projections and Transformations/Raster/Project Raster" tool. Select the tif you just created as the input file. Give the output file a slightly different name, such as "sunland27.tif" Select as your output coordinate system "Projected Coordinate Systems/Utm/NAD1927/NAD1927 UTM Zone 11N" and then click OK on the tool.

That's it! I'll provide instructions for getting the aerial-photography image back to our library later.