Changes between Version 90 and Version 91 of WKTRasterTutorial01


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Timestamp:
Aug 22, 2010, 6:31:59 PM (14 years ago)
Author:
tylere
Comment:

minor grammar correction

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  • WKTRasterTutorial01

    v90 v91  
    180180Vectorizing all the table would have been way too long and the huge number of geometry would have been impossible to load in OpenJUMP (and most GIS software).
    181181
    182 First notice: some pixels are grouped together into complex polygons. ST_DumpAsPolygons() not only blindly dump each pixels, it actually vectorize the raster grouping areas with shared values together. In a raster having a low range of values, this would result in a significantly lower number of polygons than the number of pixels. A higher number of different values (like continuous floating point value rasters) would result in many, many little polygons, most of them square corresponding to only one pixel. A future ST_Reclass() function should help reducing the number of value in a raster and give more analysis flexibility. For now you can always reclassify your raster BEFORE loading them into PostGIS WKT Raster.
     182First notice: some pixels are grouped together into complex polygons. ST_DumpAsPolygons() not only blindly dump each pixels, it actually vectorize the raster grouping areas with shared values together. In a raster having a low range of values, this would result in a significantly lower number of polygons than the number of pixels. A higher number of different values (like continuous floating point value rasters) would result in many, many little polygons, most of them square corresponding to only one pixel. A future ST_Reclass() function should help reducing the number of values in a raster and give more analysis flexibility. For now you can always reclassify your raster BEFORE loading them into PostGIS WKT Raster.
    183183
    184184This query includes the value associated each group of pixel. You can display those values by right-clicking on the OpenJUMP layer, selecting "Change Styles...", selecting the "Labels" tab, "Enabling labelling" and selecting the "val" Label attribute.