# Changes between Version 47 and Version 48 of PostGIS_Raster_SoC_Idea_2012/Distance_Analysis_Tools

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06/18/12 22:39:53 (11 months ago)
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• ## PostGIS_Raster_SoC_Idea_2012/Distance_Analysis_Tools

v47 v48
140140          The maximum distance to be generated. All pixels beyond this distance will be assigned the nodata value.
141141      * '''Algorithm:'''
142         * d(dx,dy) = sqrt(dx^2 + dy^2)
142        * d(dx,dy) = sqrt(dx^2^ + dy^2^)
143143        * Cells grown would form isolines of distance that are circular from a given point, with the distance given by the radius.
144144      * '''Reference:''' [[BR]]

366366   b. Utilize ST_SetValue(raster rast, geometry pt, double newvalue) function to designate source pixels in the resulting raster where vector source point(s) intersect(s) with the new raster.We want to assign “0” as new pixel value to pixels as source pixel(point) since the Euclidean distance from source to itself is zero.
367367   c. Calculate Euclidean distance from the center of source pixel(s) to each pixel in the raster:[[BR]]
368      d(dx,dy) = sqrt(dx^2 + dy^2)[[BR]]
368     d(dx,dy) = sqrt(dx^2^ + dy^2^)[[BR]]
369369     Unit is pixel/cell
370370   d. Set pixel value to the resulted distance[[BR]]

474474     Generate one single raster (rectan) in which pixel values represent the Euclidean distance from the center of the pixels to the center of the source point.
475475   * Proposed Algorithm:
476      * Calculate Euclidean distance using the coordinates of the center of pixel and the center of the source point (d(dx,dy) = sqrt(dx^2 + dy^2)).  If distance exceed max_distance specified, NoData value is used instead.
476     * Calculate Euclidean distance using the coordinates of the center of pixel and the center of the source point (d(dx,dy) = sqrt(dx^2^ + dy^2^)).  If distance exceed max_distance specified, NoData value is used instead.
477477     * Create a single raster with distance as pixel value (ST_RasterFromText()?) using dimensions and georeferencing information specified
478478