PostGIS Raster : Extending PostgreSQL for The Support of ... - CoDE

SELECT rast As origin, ST_Resample(rast,100,100) As reduce_100
FROM dummy_rast;
With this query, all rasters will be resampled into new dimension 100x100 using NearestNeighbor
algorith by default.
• Rescale rasters Rescaling a raster corresponds to resample a raster by adjusting its scale (or pixel
size). New pixel values are computed using the NearestNeighbor, Bilinear, Cubic, CubicSpline
or Lanczos resampling algorithm. Default is NearestNeighbor. The following example rescales
rasters to a pixel size of 0.0015 using ST_Rescale(raster, scalexy, algorithm).
SELECT ST_Rescale(rast,0.0015)
FROM dummy_rast;
• Snap rasters to different grid This operation corresponds to resample a raster by snapping it
to a grid defined by an arbitrary pixel corner and optionally a pixel size. New pixel values
are computed using the NearestNeighbor, Bilinear, Cubic, CubicSpline or Lanczos resampling
algorithm. Default is NearestNeighbor. The simple example below uses ST_SnapToGrid(raster,
cornerx, cornery, algorithm) function to snap a raster to a slightly different grid defined by the
pixel corner (0.0002, 0.0002):
SELECT ST_SnapToGrid(rast,0.0002, 0.0002)
FROM dummy_rast;
5.1.3 Vector to Raster Conversion
The example below creates a raster containing a black circle using ST_AsRaster(geometry, width,
height, pixeltype) function. Its dimensions are 150x150 pixels and its pixel type is 2-bit unsigned
integer (2BUI):
SELECT ST_AsRaster(ST_Buffer(ST_Point(1,5),10),150, 150, ’2BUI’);
where ST_Buffer is used to return a geometry that represents all points whose distance from the
point (1,5) is less than or equal to 10 pixels.
5.1.4 Raster to Vector Conversion
Figure 5.1: Raster circle [17].
The conversion using ST_DumpAsPolygons(raster, band) returns a set of geomval (formed by a
geometry and a pixel band value) rows from a given raster band. Default band number is 1. Each
geometry is the union of all pixels that have the same pixel value.
SELECT (ST_DumpAsPolygons(rast)).*
FROM dummy_rast
WHERE rid = 1;
64