I had the same problem. I ended up using the Quantum GIS function, Sum Line Lengths. Input can be your postgis line features. It adds up the lengths of the portion of each line that crosses a particular grid cell. You need to create a polygon fishnet matching your raster extent and resolution first, then convert to raster. This might actually be a better measure of density then counting lines.
- John John Callahan Research Scientist Delaware Geological Survey University of Delaware http://www.dgs.udel.edu [email protected] On Sat, Dec 22, 2012 at 9:57 PM, Jeff Adams - NOAA Affiliate < [email protected]> wrote: > Thanks for the response Stephen.I will have upwards of 150,000 lines > features that I will want to feed into the density. These are stored in a > single table (actually will be in a CTE), and many of the lines will > overlap one another. It is hard to say whether these solutions are viable > as I am having a hard time visualizing the SQL. You would think that I am > not the first person who has wanted to do this in PostGIS, but I haven't > found example one. > > On Sat, Dec 22, 2012 at 6:02 PM, Stephen Woodbridge < > [email protected]> wrote: > >> On 12/22/2012 3:07 PM, Jeff Adams - NOAA Affiliate wrote: >> >>> Hi, >>> >>> I was wondering if anybody knew of a way to create a very simple line >>> density raster. I am not interested in interpolation or clustering, >>> simply how many line features pass through each pixel in the raster. I >>> know how to do this with points, but am having difficulty figuring out >>> how to do it with lines. Any help would be greatly appreciated... >>> >> >> Separate from the SQL, you probably need to have a strategy for doing >> this. so with a point I assume you just increment the point in the raster >> for each point. So with a line we want to increment the all the raster >> points along the line. Some options: >> >> 1. render the line into an empty raster then add that raster to your >> master raster. Where add will increment by one every set raster point in >> the rendered line. >> >> 2. segmentize the line into segments that are the size of a pixel in your >> master raster and then add the midpoints of those segments to your master >> raster. >> >> Would one of these work for you? >> >> -Steve >> >> ______________________________**_________________ >> postgis-users mailing list >> [email protected] >> http://lists.osgeo.org/cgi-**bin/mailman/listinfo/postgis-**users<http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users> >> > > > > -- > Jeffrey D. Adams > Contractor > OAI, Inc. > In support of: > National Marine Fisheries Service > Office of Protected Resources > 1315 East West Hwy, Building SSMC3 > Silver Spring, MD 20910-3282 > phone: (301) 427-8434 > fax: (301) 713-0376 > _______________________________________________ > postgis-users mailing list > [email protected] > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > >
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