ST_compress-PolarDB(PolarDB)-阿里云帮助中心

Compresses a pcpatch object using the specified compression method.

Syntax

pcpatch ST_compress(pcpatch pc, text global_compression_schema default '', text compression_config default '');

Parameter	Description
`pc`	The `pcpatch` object to compress.
`global_compression_schema`	The compression method to apply. Defaults to an empty string. For valid values, see Compression schemas.
`compression_config`	The per-dimension compression algorithm. Applies only when `global_compression_schema` is set to `dimension`. Defaults to an empty string.

The global_compression_schema parameter accepts the following values:

auto — determines the compression method based on the pcid.
dimension — applies per-dimension compression. When using this schema, set compression_config to one of the following algorithms:
- auto — selects the algorithm automatically based on value statistics.
- zlib — deflate compression.
- sigbits — significant bits removal.
- rle — run-length encoding.
laz — no compression config supported.
ght — is discarded.

The following example compresses a patch created from three points and returns the result as text.

SELECT ST_asText(ST_Compress(ST_MakePatch(1, ARRAY[-126.99,45.01,1,0, -126.98,45.02,2,0, -126.97,45.03,3,0])));

Output:

{"pcid":1,"pts":[
 [-126.99,45.01,1,0],[-126.98,45.02,2,0],[-126.97,45.03,3,0]
]}