Changes between Version 30 and Version 31 of PostGIS_Raster_SoC_Idea_2012/Distance_Analysis_Tools/document
- Timestamp:
- Jul 15, 2012, 8:04:57 PM (12 years ago)
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PostGIS_Raster_SoC_Idea_2012/Distance_Analysis_Tools/document
v30 v31 32 32 ==== 1. The raster source approach ==== 33 33 34 The first approach is similar to what is found in most GIS package. The source points (or geometries) are converted to a raster of sources and this raster is passed to the function. The function iterates over the pixels (__or over the source points???__) assigning the distance to the nearest point (__or assigning minimum values to pixels within a circle progressively growing around each point???__).34 The first approach is similar to what is found in most GIS package. The source points (or geometries) are converted to a raster of sources and this raster is passed to the function. The function iterates over the pixels (__or over the source points???__) (__I think most GIS packages do the iterration over the pixels?__) assigning the distance to the nearest point (__or assigning minimum values to pixels within a circle progressively growing around each point???__)(__some of them used growing method like GRASS__). 35 35 36 36 Converting one or a set of source geometries to one raster can be performed like this in PostGIS: … … 70 70 * Producing an intermediate raster is costly if the requested raster resolution is very high (constraint 3, 5b & 5d). 71 71 * ST_Union could be very inefficient at producing the required raster from a large set of geometries and there is no efficient method to produce such a raster right now in PostGIS (constraints 1, 5c & 5d). 72 * It could be very inefficient to rescan all the source points to find the one nearest to the current pixel (constraint 6, 7, 8 & 12). __We still have to see how GRASS does this efficiently.__ 72 * It could be very inefficient to rescan all the source points to find the one nearest to the current pixel (constraint 6, 7, 8 & 12). __We still have to see how GRASS does this efficiently.__ (I was wrong about this. What I found in GDAL and GRASS is that they only scan the pixels not for all the source points to each pixel) 73 73 * Only rasters which extent contains all the source points could be produced. 74 74 * This approach does not answer well to the requirement of developing a generic reusable solution for more interpolation needs (constraint 7).