Submitted by dylan on Fri, 2006-07-21 23:45.
After a bit of a delay, I have finally migrated all of the USDA-NCSS digital soil survey (AZ, CA, NV), 2005se Tiger, and other misc. data from shapefile format to a PostGIS database. In doing so, seamless access to the entire set of detailed (SSURGO) and generalized (STATSGO) polygon data is now possible through our online soil survey. At the Map unit level, links to adjacent soil polygons, along with a local area calculation are just some of the new possibilities of a spatially-enabled database (PostGIS). Note that DOQQ data is not locally stored for AZ and NV. Clicking on the "print" icon in the map interface at scale of < 1:7000 will fetch DOQQ data from Terraserver in these areas. Also the LandSat mosaic for AZ needs to be re-done with i.landsat.rgb, found in GRASS6.1-CVS. A quick comparison of LandSat channel blending is here. Subsequent changes will include thematic mapping of soil properties and visualizations of difference in soil properties across scales. See a simple summary, in case-study format on the PostGIS website. Thanks to Paul Ramsey for doing the write-up.
Submitted by dylan on Wed, 2006-06-14 00:06.
Submitted by dylan on Fri, 2006-02-03 04:14.
Submitted by dylan on Fri, 2006-02-03 03:37.
Depicting the relative density of sampling can be an interesting task, especially when the points are highly clustered and sparse. Three simple operations that can reveal subtle patterns in the spatial distribution of sample points were explored:
Submitted by dylan on Thu, 2006-02-02 22:32.
Raw LiDAR data is so detailed that localized flow routing algorithms often fail to produce meaningful results. The terraflow algorithm is one such method that appears to work well on such massive grid objects (Homepage).
Submitted by dylan on Mon, 2006-01-02 18:57.
Submitted by dylan on Wed, 2005-09-28 23:12.
More often than not geographic data come in a format that is essentially two-dimensional: i.e. raster grids and vector points, lines, and areas with only (x,y) style coordinates.
Submitted by dylan on Mon, 2005-08-22 22:23.
Submitted by dylan on Thu, 2005-08-11 00:10.
100 iterations of mass removal based on preferential flow of water as calculated by r.topidx in GRASS. Notice how landform is cutdown most in stream channels, least at the ridges. The basins between ridges appear to "fill" with sediment near the 50th iteration as the entire landform is lowered to sea level (0m). Absolute change in elevation is visble in the elevation profiles below. Example GRASS commands below. Here is a link to a movie, containing all 100 iterations.
Submitted by dylan on Tue, 2005-07-19 21:31.