[postgis-users] How do you use PostGIS Raster?

[Bryce L Nordgren]

Pierre Racine <Pierre.Racine at sbf.ulaval.ca> 
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06/07/2011 07:30 PM
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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-bounces at postgis.refractions.net 
[mailto:postgis-users-bounces at 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_______________________________________________
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