>Thanks for the reference Doug. What you suggest does sound like it could >work, the only thing is that >I would need to have this output as a Raster as I am then looking to use it >with two other rasters >to do a weighted combination of them e.g. [rast1 * 0.2] + [rast2 * 0.5] + ?[rast3 * 0.3].
>Do you know how if I could easily rasterise the output of what you've >suggested? James, Unfortunately, I have not waded into rasters inside postgis yet. I'm speculating that you could generate a raster from the point values you generated from the suggested calculation. ( Using St_AsRaster, http://postgis.refractions.net/docs/RT_ST_AsRaster.html ?) For raster algebra, I usually use GRASS r.mapcalculator - http://grass.fbk.eu/gdp/html_grass64/r.mapcalculator.html. If you can dump your images out to files, you could import them to grass ( or use r.external to link to them) and perform the calculation you described. If you want to stay in postgis, just do the calculation in two steps. >Only reason is I'm working on it for a dissertation project and I've left >myself little time left to consider this. Sounds like my grad school experience :-) Doug Doug Newcomb USFWS Raleigh, NC 919-856-4520 ext. 14 doug_newc...@fws.gov --------------------------------------------------------------------------------------------------------- The opinions I express are my own and are not representative of the official policy of the U.S.Fish and Wildlife Service or Dept. of the Interior. Life is too short for undocumented, proprietary data formats. JamesH <james.hol...@newcastle.ac.uk> Sent by: postgis-users-boun...@postgis.refractions.net 04/25/2012 02:49 PM Please respond to PostGIS Users Discussion <postgis-users@postgis.refractions.net> To postgis-users@postgis.refractions.net cc Subject Re: [postgis-users] Simple Point Density Surface "Why not convert the raster cell centers to points , do a query on the point layer for a square centered on the raster derived point whose dimensions are given by the number of tiles in your neighborhood. return the number of points divided by the area of the square. ( neighborhoods are usually odd numbers of cells, 3x3, 5x5, etc so you have an equal number around the center cell)" Thanks for the reference Doug. What you suggest does sound like it could work, the only thing is that I would need to have this output as a Raster as I am then looking to use it with two other rasters to do a weighted combination of them e.g. [rast1 * 0.2] + [rast2 * 0.5] + [rast3 * 0.3]. Do you know how if I could easily rasterise the output of what you've suggested? Only reason is I'm working on it for a dissertation project and I've left myself little time left to consider this. Kind Regards, James ----- GIS Undergraduate -- View this message in context: http://postgis.17.n6.nabble.com/Simple-Point-Density-Surface-tp4917343p4917632.html Sent from the PostGIS - User mailing list archive at Nabble.com. _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
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