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Open Source GIS and Mapping IdeasAggregating SSURGO Data in RSubmitted by dylan on Thu, 2009-09-10 15:36.
If you happen to have some of the SSURGO tabular data that includes column names, the following R code may be of general interest for resolving the 1:many:many hierarchy of relationships required to make a thematic map.
mukey clay silt sand water_storage
458581 20.93750 20.832237 20.861842 14.460000
458584 43.11513 30.184868 26.700000 23.490000
458593 50.00000 27.900000 22.100000 22.800000
458595 34.04605 14.867763 11.776974 18.900000
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Simple Approach to Converting GRASS DB-backendsSubmitted by dylan on Sat, 2009-05-23 21:32.
Currently GRASS uses a single SQLite (file-based) database per mapset-- convenient if you are interested in joining attribute tables between vectors; but not set-in-stone as the final approach that will be used by default in GRASS 7. Regardless, converting the back-end is a fairly simple matter. Finally, taking the time to convert to an SQLite or Postgresql back-end will undoubtably save you time and sanity if you ever find yourself working with vector+attribute data on a regular basis. Having access to a complete implementation of SQL can make extracting, summarizing, joining, and re-formatting (column names, types, etc.) tabular data much simpler than what is available in the DBF back-end. Also, there are several convenient graphical SQLite managers available, such as SQLite manager, SQLite data browser, and SQLite Admin. ( categories: )
Traveling Salesman Approach to Visiting Data-loggersSubmitted by dylan on Sat, 2008-12-20 06:44.
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Batch Projection and Masking with GRASSSubmitted by dylan on Wed, 2008-05-07 18:21.
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Simple Python Interface to USGS TNM Elevation ServiceSubmitted by dylan on Tue, 2008-04-29 06:31.
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Detailed Magnetic DeclinationSubmitted by dylan on Fri, 2008-03-14 20:45.
Setting the magnetic declination on a compass is a critical step in accurate measurement of bearings that can be translated to map or survey. As the location of the magnetic north pole is constantly moving, the magnetic declination reported on older topographic maps or compass housings are probably out of date. Current declination values for a single point, or for large regions can be found on the NOAA sites: These resources are helpful, but a current, detailed (state-level) map of magnetic declination would be interesting. ( categories: )
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