PostGIS
Name
ST_Aspect — Returns the aspect (in degrees by default) of an elevation raster band. Useful for analyzing terrain.
Synopsis
raster +`*`+ST_Aspect*(`raster `rast, integer band=1, text
pixeltype=32BF, text units=DEGREES, boolean
interpolate_nodata=FALSE`)`;
raster +`*`+ST_Aspect*(`raster `rast, integer band, raster
customextent, text pixeltype=32BF, text units=DEGREES,
boolean interpolate_nodata=FALSE`)`;
Description
Returns the aspect (in degrees by default) of an elevation raster band. Utilizes map algebra and applies the aspect equation to neighboring pixels.
units indicates the units of the aspect. Possible values are:
RADIANS, DEGREES (default).
When units = RADIANS, values are between 0 and 2 * pi radians
measured clockwise from North.
When units = DEGREES, values are between 0 and 360 degrees measured
clockwise from North.
If slope of pixel is zero, aspect of pixel is -1.
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Availability: 2.0.0
Enhanced: 2.1.0 Uses ST_MapAlgebra() and added optional
interpolate_nodata function parameter
Changed: 2.1.0 In prior versions, return values were in radians. Now, return values default to degrees
Examples: Variant 1
WITH foo AS (
SELECT ST_SetValues(
ST_AddBand(ST_MakeEmptyRaster(5, 5, 0, 0, 1, -1, 0, 0, 0), 1, '32BF', 0, -9999),
1, 1, 1, ARRAY[
[1, 1, 1, 1, 1],
[1, 2, 2, 2, 1],
[1, 2, 3, 2, 1],
[1, 2, 2, 2, 1],
[1, 1, 1, 1, 1]
]::double precision[][]
) AS rast
)
SELECT
ST_DumpValues(ST_Aspect(rast, 1, '32BF'))
FROM foo
st_dumpvalues
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
----------------------------------
(1,"{{315,341.565063476562,0,18.4349479675293,45},{288.434936523438,315,0,45,71.5650482177734},{270,270,-1,90,90},{251.565048217773,225,180,135,108.434951782227},{225,198.43495178
2227,180,161.565048217773,135}}")
(1 row)Examples: Variant 2
Complete example of tiles of a coverage. This query only works with PostgreSQL 9.1 or higher.
WITH foo AS (
SELECT ST_Tile(
ST_SetValues(
ST_AddBand(
ST_MakeEmptyRaster(6, 6, 0, 0, 1, -1, 0, 0, 0),
1, '32BF', 0, -9999
),
1, 1, 1, ARRAY[
[1, 1, 1, 1, 1, 1],
[1, 1, 1, 1, 2, 1],
[1, 2, 2, 3, 3, 1],
[1, 1, 3, 2, 1, 1],
[1, 2, 2, 1, 2, 1],
[1, 1, 1, 1, 1, 1]
]::double precision[]
),
2, 2
) AS rast
)
SELECT
t1.rast,
ST_Aspect(ST_Union(t2.rast), 1, t1.rast)
FROM foo t1
CROSS JOIN foo t2
WHERE ST_Intersects(t1.rast, t2.rast)
GROUP BY t1.rast;