Raster Processing: DEM (Elevation)
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.
Note
For more information about Slope, Aspect and Hillshade, please refer to ESRI - How hillshade works and ERDAS Field Guide - Aspect Images.
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;
See Also
RT_ST_MapAlgebra, RT_ST_TRI, RT_ST_TPI, RT_ST_Roughness, RT_ST_HillShade, RT_ST_Slope
ST_HillShade
Returns the hypothetical illumination of an elevation raster band using provided azimuth, altitude, brightness and scale inputs.
Synopsis
raster ST_HillShade(raster rast, integer band=1, text pixeltype=32BF, double precision azimuth=315, double precision altitude=45, double precision max_bright=255, double precision scale=1.0, boolean interpolate_nodata=FALSE)
raster ST_HillShade(raster rast, integer band, raster customextent, text pixeltype=32BF, double precision azimuth=315, double precision altitude=45, double precision max_bright=255, double precision scale=1.0, boolean interpolate_nodata=FALSE)
Description
Returns the hypothetical illumination of an elevation raster band using the azimuth, altitude, brightness, and scale inputs. Utilizes map algebra and applies the hill shade equation to neighboring pixels. Return pixel values are between 0 and 255.
azimuth is a value between 0 and 360 degrees measured clockwise from North.
altitude is a value between 0 and 90 degrees where 0 degrees is at the horizon and 90 degrees is directly overhead.
max_bright is a value between 0 and 255 with 0 as no brightness and 255 as max brightness.
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 RT_ST_InvDistWeight4ma before computing the hillshade illumination.
Note
For more information about Hillshade, please refer to How hillshade works.
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, azimuth and altitude were expressed in radians. Now, azimuth and altitude are expressed in 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_Hillshade(rast, 1, '32BF'))
FROM foo
st_dumpvalues
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------
(1,"{{NULL,NULL,NULL,NULL,NULL},{NULL,251.32763671875,220.749786376953,147.224319458008,NULL},{NULL,220.749786376953,180.312225341797,67.7497863769531,NULL},{NULL,147.224319458008
,67.7497863769531,43.1210060119629,NULL},{NULL,NULL,NULL,NULL,NULL}}")
(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_Hillshade(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;
See Also
RT_ST_MapAlgebra, RT_ST_TRI, RT_ST_TPI, RT_ST_Roughness, RT_ST_Aspect, RT_ST_Slope
ST_Roughness
Returns a raster with the calculated "roughness" of a DEM.
Synopsis
raster ST_Roughness(raster rast, integer nband, raster customextent, text pixeltype="32BF", boolean interpolate_nodata=FALSE)
Description
Calculates the "roughness" of a DEM, by subtracting the maximum from the minimum for a given area.
Availability: 2.1.0
Examples
-- needs examples
See Also
RT_ST_MapAlgebra, RT_ST_TRI, RT_ST_TPI, RT_ST_Slope, RT_ST_HillShade, RT_ST_Aspect
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 RT_ST_InvDistWeight4ma before computing the surface slope.
Note
For more information about Slope, Aspect and Hillshade, please refer to ESRI - How hillshade works and ERDAS Field Guide - Slope Images.
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;
See Also
RT_ST_MapAlgebra, RT_ST_TRI, RT_ST_TPI, RT_ST_Roughness, RT_ST_HillShade, RT_ST_Aspect
ST_TPI
Returns a raster with the calculated Topographic Position Index.
Synopsis
raster ST_TPI(raster rast, integer nband, raster customextent, text pixeltype="32BF", boolean interpolate_nodata=FALSE)
Description
Calculates the Topographic Position Index, which is defined as the focal mean with radius of one minus the center cell.
Note
This function only supports a focalmean radius of one.
Availability: 2.1.0
Examples
-- needs examples
See Also
RT_ST_MapAlgebra, RT_ST_TRI, RT_ST_Roughness, RT_ST_Slope, RT_ST_HillShade, RT_ST_Aspect
ST_TRI
Returns a raster with the calculated Terrain Ruggedness Index.
Synopsis
raster ST_TRI(raster rast, integer nband, raster customextent, text pixeltype="32BF", boolean interpolate_nodata=FALSE)
Description
Terrain Ruggedness Index is calculated by comparing a central pixel with its neighbors, taking the absolute values of the differences, and averaging the result.
Note
This function only supports a focalmean radius of one.
Availability: 2.1.0
Examples
-- needs examples
See Also
RT_ST_MapAlgebra, RT_ST_Roughness, RT_ST_TPI, RT_ST_Slope, RT_ST_HillShade, RT_ST_Aspect