# ST_Aspect

## 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.

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_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;
```