ST_Contour function to generate contours from raster data - ApsaraDB RDS

Generates contour lines or filled polygons from a digital elevation model (DEM) raster band.

Syntax

set of record ST_Contour(
    raster rast,
    integer band,
    cstring contourOptions);

Parameters

Parameter	Description
`rast`	The raster object. Must be a DEM with exactly one band.
`band`	The band number. Starts from 0.
`contourOptions`	A JSON string that controls contour generation. See the fields below.

contourOptions fields

Field	Type	Default	Description
`level_base`	float	0.0	The starting offset for contour values. For example, with `level_base=5` and `interval=10`, contours are generated at 5, 15, 25, and so on.
`fixed_level`	float array	None	An explicit list of contour values (e.g., `[100, 200, 300]`). When specified, `interval` is ignored.
`interval`	float	None	The spacing between contours. Used only when `fixed_level` is not specified.
`polygonize`	bool	false	The output type. `false` returns each contour as a closed curve. `true` fills the area between adjacent contours with DEM values and returns polygons.
`nodata`	float	-1.0	The nodata value.

Description

ST_Contour processes the specified raster band and returns a set of records — one per contour line or filled polygon.

Choosing between `fixed_level` and `interval`: Use fixed_level to generate contours at exact elevations (e.g., [100, 200, 500]). Use interval for evenly spaced contours across the full elevation range. If both are specified, fixed_level takes precedence and interval is ignored.

Each returned record contains the following fields:

Field	Type	Description
`id`	integer	The sequence number of the contour line or polygon.
`min_value`	float	The minimum DEM value in the contour line or polygon. For a DEM input, this is the lower elevation bound of that contour band.
`max_value`	float	The maximum DEM value in the contour line or polygon. For a DEM input, this is the upper elevation bound of that contour band.
`geom`	geometry	The geometry of the contour line or polygon.

Examples

Generate contour lines at a fixed interval

SELECT (ST_Contour(rast, 0, '{"interval": "2.0"}')).*
FROM raster_table
WHERE id = 1;

Generate filled polygons at specific elevations

SELECT (ST_Contour(rast, 0, '{
    "fixed_level": [1, 5, 10, 15, 20, 30],
    "polygonize": "true"
}')).*
FROM raster_table
WHERE id = 1;

Generate filled polygons with a custom base and nodata value

SELECT (ST_Contour(rast, 0, '{
    "interval": "5",
    "level_base": "1.0",
    "nodata": "0.0",
    "polygonize": "true"
}')).*
FROM raster_table
WHERE id = 1;