Changes between Version 27 and Version 28 of WKTRasterGSoC


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Timestamp:
Apr 2, 2013, 3:39:58 PM (11 years ago)
Author:
robe
Comment:

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  • WKTRasterGSoC

    v27 v28  
    11
    2 == Google Summer of Code 2012 PostGIS Raster Ideas ==
     2== Google Summer of Code PostGIS Raster Ideas ==
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    15 ~~ '''2) An optimized version of the two rasters ST_MapAlgebra SQL function'''
     15~~ '''2) An optimized version of the two rasters ST_MapAlgebra SQL function''' -- Bborie has already done this.
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    1717 Mentor: Pierre Racine (pierre.racine at sbf.ulaval.ca)
    … …  
    2020 [http://www.quantdec.com/SYSEN597/GTKAV/section9/map_algebra.htm Map algebra] allows the creation of a new raster as a mathematical (or logical) function of one or two other rasters. e.g. raster3 = (raster1 + raster2) / 2. This is a very common raster operation in the GIS world.
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    22  A [http://postgis.refractions.net/documentation/manual-svn/RT_ST_MapAlgebraExpr2.html two rasters version of the ST_MapAlgebra SQL function already exist]. It allows a PostGIS user to create a new raster coverage as a function of two existing one with a simple SQL query. e.g.: SELECT ST_MapAlgebra(rast1, rast2, "(rast1 + rast2) / 2") FROM coverage1, coverage2 WHERE ST_Intersects(rast1, rast2). The extent of the resulting raster can be equivalent to the extent of the FIRST, the SECOND, the INTERSECTION or the UNION of both raster.
     22 A [http://postgis.net/docs/manual-dev/RT_ST_MapAlgebraExpr two rasters version of the ST_MapAlgebra SQL function already exist]. It allows a PostGIS user to create a new raster coverage as a function of two existing one with a simple SQL query. e.g.: SELECT ST_MapAlgebra(rast1, rast2, "(rast1 + rast2) / 2") FROM coverage1, coverage2 WHERE ST_Intersects(rast1, rast2). The extent of the resulting raster can be equivalent to the extent of the FIRST, the SECOND, the INTERSECTION or the UNION of both raster.
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    2424 The current implementation compute the new raster one pixel at a time. It is possible, but complicated, to optimize the algorythm in order to fill many areas as a chunck of data instead of pixels by pixels. The project includes reviewing the proposed algorythm and implementing it. You will familiarize yourself with PostGIS development (the most used open source geospatial database), geospatial imagery concepts, open source development tools and code in C and PL/pgSQL. ~~~