Pierre Racine <pierre.rac...@sbf.ulaval.ca> Sent by: postgis-users-boun...@postgis.refractions.net 06/07/2011 07:30 PM Please respond to PostGIS Users Discussion <postgis-users@postgis.refractions.net>
To PostGIS Users Discussion <postgis-users@postgis.refractions.net> cc Subject Re: [postgis-users] How do you use PostGIS Raster? What are you missing to implement any of those in PostGIS raster? For the first thing: maybe nothing, but I'd have to check. It would be convenient if there was a "rasterize" function which would serve as the inverse of a ST_DumpAsPolygons(). For the second thing: Landsat scenes are ~7000x8000 pixels; ST_DumpAsPolygons() gives a huge set of geometries. The MODIS fire perimeters are also huge. The first step is a "global" (image-wide) analysis. It was very slow when I tried it. We need an ST_Intersection that returns a clipped raster; and we also need an ST_Union() or ST_Collect() which returns an aggregated raster. From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users-boun...@postgis.refractions.net] On Behalf Of Bryce L Nordgren Sent: Tuesday, June 07, 2011 3:12 PM To: PostGIS Users Discussion Subject: Re: [postgis-users] How do you use PostGIS Raster? I'm not using PostGIS raster yet. We've been using PostGIS for years to keep track of active fire and burn scar detections from the MODIS instruments on board the Aqua and Terra satellites. Part of our process is to resample the point detections onto a grid which aggregates burned area over the course of a fire season. Aggregating onto a grid has been performed using an external program, but we'd like to be able to use PostGIS raster. More recently, we're comparing a vector fire perimeter from the MODIS instrument to a higher resolution Landsat image of the area. We select the areas of the Landsat raster which are inside the perimeter vs. outside the perimeter and calculate histograms on the separate image regions. Currently, we're using ENVI and IDL to do this more or less manually. We'd like to be able to perform this inside PostGIS, as PostGIS is the source of the vector data anyway. Bryce_______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
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