PostGIS
Name
ST_Slope — Returns the slope (in degrees by default) of an elevation raster band. Useful for analyzing terrain.
Synopsis
raster +`*`+ST_Slope*(`raster `rast, integer nband=1, text
pixeltype=32BF, text units=DEGREES, double precision
scale=1.0, boolean interpolate_nodata=FALSE`)`;
raster +`*`+ST_Slope*(`raster `rast, integer nband, raster
customextent, text pixeltype=32BF, text units=DEGREES,
double precision scale=1.0, boolean
interpolate_nodata=FALSE`)`;
Description
Returns the slope (in degrees by default) of an elevation raster band. Utilizes map algebra and applies the slope equation to neighboring pixels.
units indicates the units of the slope. Possible values are:
RADIANS, DEGREES (default), PERCENT.
scale is the ratio of vertical units to horizontal. For Feet:LatLon
use scale=370400, for Meters:LatLon use scale=111120.
If interpolate_nodata is TRUE, values for NODATA pixels from the
input raster will be interpolated using
ST_InvDistWeight4ma before computing
the surface slope.
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Availability: 2.0.0
Enhanced: 2.1.0 Uses ST_MapAlgebra() and added optional units,
scale, interpolate_nodata function parameters
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_Slope(rast, 1, '32BF'))
FROM foo
st_dumpvalues
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
---------------------------------------------------------------------
(1,"{{10.0249881744385,21.5681285858154,26.5650520324707,21.5681285858154,10.0249881744385},{21.5681285858154,35.2643890380859,36.8698959350586,35.2643890380859,21.5681285858154},
{26.5650520324707,36.8698959350586,0,36.8698959350586,26.5650520324707},{21.5681285858154,35.2643890380859,36.8698959350586,35.2643890380859,21.5681285858154},{10.0249881744385,21.
5681285858154,26.5650520324707,21.5681285858154,10.0249881744385}}")
(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_Slope(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;