ST_Polygonize to vectorize a raster by pixel value - PolarDB

Vectorizes a raster band by pixel value, returning one (geom, id, value) row per contiguous region of identical pixel values.

Syntax

setof record ST_Polygonize(
    raster  rast,
    integer bandnumber,
    cstring options,
    out geom  geometry,
    out id    integer,
    out value float8
);

Parameters

Parameter	Type	Required	Description
`rast`	raster	Yes	The input grid object.
`bandnumber`	integer	Yes	The band to vectorize. Band numbering starts at 0.
`options`	cstring	No	A JSON string with vectorization options. If omitted, defaults apply.

Output columns

Column	Type	Description
`geom`	geometry	The polygon geometry for a contiguous pixel region.
`id`	integer	A sequential identifier for each output row.
`value`	float8	The pixel value shared by all pixels in the region.

options fields

Field	Type	Default	Description
`ingoreValue`	float	0	A pixel value to exclude from vectorization. Pixels with this value are not converted to polygons.

ingoreValue and NoData are separate exclusion mechanisms. NoData pixels are always excluded from vectorization regardless of the ingoreValue setting. Use ingoreValue to additionally exclude a specific valid pixel value (for example, background pixels with value 0).

Example

The following query vectorizes band 1 of the raster in rast_table where id = 1, excluding pixels with value 0:

select ST_Polygonize(rast, 1, '{"ingoreValue":0}') from rast_table where id = 1;

Input raster

Output polygons

Each output row contains a polygon geometry (geom), a row identifier (id), and the pixel value (value) for that region.