Changes between Version 30 and Version 31 of PostGIS_Raster_SoC_Idea_2012/Distance_Analysis_Tools/document

Show
Ignore:
Timestamp:
07/15/12 20:04:57 (10 months ago)
Author:
qliu
Comment:

--

Legend:

Unmodified
Added
Removed
Modified

  • PostGIS_Raster_SoC_Idea_2012/Distance_Analysis_Tools/document

    v30 v31  
    3232==== 1. The raster source approach ==== 
    3333 
    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__). 
    3535 
    3636  Converting one or a set of source geometries to one raster can be performed like this in PostGIS: 
    … …  
    7070 * Producing an intermediate raster is costly if the requested raster resolution is very high (constraint 3, 5b & 5d).  
    7171 * 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) 
    7373 * Only rasters which extent contains all the source points could be produced. 
    7474 * This approach does not answer well to the requirement of developing a generic reusable solution for more interpolation needs (constraint 7).