This function computes the aspect from each cell of a raster surface and returns an array of aspects.
Syntax
float8[] ST_Aspect(raster rast, integer pyramid_level, integer band, Box extent, BoxType type);
Parameters
Parameter | Description |
---|---|
rast | The raster object. |
pyramid_level | The pyramid level. |
Band | The sequence number of the band. |
box | The area to be analyzed, in the format of '((minX,minY),(maxX,maxY))' .
|
type | The coordinate type of the area to be analyzed. Valid values:
|
Description
The aspect function identifies the downslope direction of the maximum rate of change in value from each cell to its neighbors. The aspect can be thought of as the slope direction. The value of each cell in the output raster indicates the compass direction that the surface faces at that location. The aspect is measured clockwise in degrees from 0 (due north) to 360 (again due north), which comes full circle. Cells that are flat, which have no downslope direction, are assigned an aspect of -1 in the output raster.
The value of each cell in the aspect dataset of the output raster indicates the slope direction of the cell.
Examples
select st_aspect(rast, 0, 0, '(0,0), (5,5)', 'Raster') from t_surface where id=1;
st_aspect
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{5.68600864908691,5.742765806909,5.08963804002705,5.2696845155022,5.67764064357462,5.91019758537953,5.37643514321137,5.
..48370356795928,5.18761908299415,5.02882043600982,4.83181790640303,4.33940125858463,5.56909460856743,5.92299216276176,.
.5.86712080145576,5.29376916418959,4.41982721398084,4.53158940708072,0.141897054604164,0.274167451119659,6.267561578559.
.11,5.742765806909,4.56734728205808,4.7215630349298,0.547562235939998,6.0814229628593,5.96909743805248,5.80535425218747.
.,4.74463586281994,4.71238898038469,0.141897054604164,6.13281387917245,6.05997388768217,5.98920538937637,4.789160871654.
.47,4.4855901323308}
(1 row)