ST_PixelWidth
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Name

ST_PixelWidth — Returns the pixel width in geometric units of the spatial reference system.

Synopsis

double precision ST_PixelWidth(raster rast);

Description

Returns the width of a pixel in geometric units of the spatial reference system. In the common case where there is no skew, the pixel width is just the scale ratio between geometric coordinates and raster pixels.

The following executable example draws the two pixel basis vectors on the same coordinate frame as a skewed raster footprint. The i direction vector is (scaleX, skewY); the j direction vector is (skewX, scaleY).

Examples

Pixel basis vectors and footprint for a raster with non-zero skew.

Code
WITH raster AS (
    SELECT ST_MakeEmptyRaster(
        3, 3, 0, 0,
        2, -3, 1, 0.5,
        0
    ) AS rast
)
SELECT
    ST_ConvexHull(rast) AS footprint,
    ST_MakeLine(
        ST_Point(0, 0),
        ST_Point(ST_ScaleX(rast), ST_SkewY(rast))
    ) AS "i direction (scaleX, skewY)",
    ST_MakeLine(
        ST_Point(0, 0),
        ST_Point(ST_SkewX(rast), ST_ScaleY(rast))
    ) AS "j direction (skewX, scaleY)"
FROM raster;
Output
POLYGON((0 0,6 1.5,9 -7.5,3 -9,0 0)) | LINESTRING(0 0,2 0.5) | LINESTRING(0 0,1 -3)
Figure
Geometry figure for visual-rt-st-pixelwidth-01

Rasters with no skew.

Code
SELECT ST_Width(rast) As rastwidth, ST_PixelWidth(rast) As pixwidth,
ST_ScaleX(rast) As scalex, ST_ScaleY(rast) As scaley, ST_SkewX(rast) As skewx,
ST_SkewY(rast) As skewy
FROM dummy_rast;
Output
    rastwidth | pixwidth | scalex | scaley | skewx | skewy
-----------+----------+--------+--------+-------+----------
10 |        2 |      2 |      3 |     0 |        0
 5 |     0.05 |   0.05 |  -0.05 |     0 |        0

Rasters with skew different than 0.

Code
SELECT ST_Width(rast) As rastwidth, ST_PixelWidth(rast) As pixwidth,
ST_ScaleX(rast) As scalex, ST_ScaleY(rast) As scaley, ST_SkewX(rast) As skewx,
ST_SkewY(rast) As skewy
FROM (SELECT ST_SetSkew(rast, 0.5, 0.5) As rast
FROM dummy_rast) As skewed;
Output
    rastwidth |     pixwidth      | scalex | scaley | skewx | skewy
-----------+-------------------+--------+--------+-------+----------
10 |  2.06155281280883 |      2 |      3 |   0.5 |      0.5
 5 | 0.502493781056044 |   0.05 |  -0.05 |   0.5 |      0.5