Changes between Version 27 and Version 28 of WKTRaster/SpecificationWorking02


Ignore:
Timestamp:
09/17/10 08:48:04 (14 years ago)
Author:
pracine
Comment:

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  • WKTRaster/SpecificationWorking02

    v27 v28  
    9898 This function is necessary to optimize ST_Intersection. The raster to be polygonised before proceeding to a vector intersection should first be clipped to the minimal intersecting area using ST_Clip().
    9999
    100 ----
    101 == '''Objective B02x - Being able to intersect vector and raster to produce raster.''' ==
    102  
    103 
    104 '''ST_Intersects(raster, raster)'''[[BR]]
    105 '''ST_AsRaster(geometry, pixelsize) -> raster'''[[BR]]
    106 '''ST_Intersection(geometry, val, raster, band) -> raster'''
    107 
    108  The first series of variant return a raster having the same extent as the provided raster.
    109 
    110   Variant 1: ST_Intersection(geometry, val, raster, band, pixeltype, nodatavalue) -> raster
    111 
    112   Variant 2: ST_Intersection(raster, band, geometry, val, pixeltype, nodatavalue) -> raster
    113 
    114   Variant 3: ST_Intersection(geometry, val, raster, pixeltype, nodatavalue) -> raster
    115 
    116   Variant 4: ST_Intersection(raster, geometry, val, pixeltype, nodatavalue) -> raster
    117 
    118  The second series of variant return a raster having the minimal extent.
    119 
    120   Variant 5: ST_Intersection(geometry, val, raster, band, pixeltype, nodatavalue, 'TRIM') -> raster
    121 
    122   Variant 6: ST_Intersection(raster, band, geometry, val, pixeltype, nodatavalue, 'TRIM') -> raster
    123 
    124   Variant 7: ST_Intersection(geometry, val, raster, pixeltype, nodatavalue, 'TRIM') -> raster
    125 
    126   Variant 8: ST_Intersection(raster, geometry, val, pixeltype, nodatavalue, 'TRIM') -> raster
    127 
    128  Return a two bands raster the first band containing only the pixels from the provided raster intersecting with the geometry and the second band containing the same area filled with the provided value.
    129 
    130  The second band gets its pixeltype and nodatavalue from the parameters.
    131 
    132  Non intersecting pixels are filled with nodata values.
    133 
    134  Variant 1 return a raster having the same extent as the provided raster.
    135 
    136  Variant 3, 4, 7 and 8 defaults the band number to 1.
    137 
    138  Variant 5 to 8 "trim" or "crop" the raster to the withvalue extent (removing extra nodata value pixels surrounding the extent of the resulting withvalue extent).
    139 
    140  
    141  '''Open question'''
    142 
    143  PR: Shoud we return one raster per raster/geometry couple or split the raster into as many small rasters as there are areas sharing a same value? The second behavior seems more coherent with the present behavior of ST_Intersection(raster, geometry) -> geometry even if this would produce tons of small two bands rasters.
    144 
    145  '''Implementation details'''
    146 
    147  Rasterize the geometry as a new raster (ST_AsRaster(geometry, pixeltype, val, nodataval, raster)) and then copy only pixels for which both raster bands have a value.
    148  Should be implemented as a wrapper around ST_MapAlgebra after rasterizing the geometry to a raster having the same alignment as the raster.
    149 
    150 ----
    151 == '''Objective B02x - Being able to use "group by" to accumulate tiles to form a new raster.''' ==
    152  
    153 
    154 '''ST_Union(raster|geometry, raster|geometry, ‘raster’|’geometry’) -> raster/geometry'''[[BR]]
    155 '''ST_Accum(raster set|geometry set, ‘raster’|’geometry’) -> raster/geometry'''
    156100
    157101----