ApsaraDB RDS:ST_HMTAsArray

Syntax

float8[][] ST_HMTAsArray(bytea hmt);

Return value

Returns a 2D float8 array. Each element represents a statistical value of the corresponding cell in the heatmap grid.

Parameters

Description

ST_HMTAsArray takes a heatmap tile generated by ST_AsHMT and converts it to a 2D float8 array. The array preserves the spatial grid structure of the heatmap, making individual cell values accessible for programmatic processing or visual inspection.

Examples

The following example creates a test table with 10 geometry points, generates a heatmap tile over a 10×10 pixel grid, and converts it to a 2D array.

CREATE TABLE test_table AS
SELECT i num,
    ST_setSRID(st_makepoint((i-0.5)::numeric, (i-0.5)::numeric), 4326) geom,
    i*100::int4 weight,
    i*i*i::float8 volume
FROM generate_series(1, 10) i;

SELECT ST_HMTAsArray(ST_AsHMT(geom,                        -- geometry column
    ST_MakeEnvelope(0, 0, 10, 10, 4326),                   -- spatial extent
    10,                                                     -- width in pixels
    10                                                      -- height in pixels
))
FROM test_table;

Expected output:

[0:9][0:9]={{1,0,0,0,0,0,0,0,0,0},{0,1,0,0,0,0,0,0,0,0},{0,0,1,0,0,0,0,0,0,0},{0,0,0,1,0,0,0,0,0,0},{0,0,0,0,1,0,0,0,0,0},{0,0,0,0,0,1,0,0,0,0},{0,0,0,0,0,0,1,0,0,0},{0,0,0,0,0,0,0,1,0,0},{0,0,0,0,0,0,0,0,1,0},{0,0,0,0,0,0,0,0,0,1}}

The output is a 10×10 array indexed [0:9][0:9]. The diagonal pattern of 1 values reflects that each of the 10 points falls in a distinct grid cell along the diagonal of the spatial extent.