Extends ST_AsMVTGeom with a res_prec parameter that filters out geometry objects too small to affect the display, reducing the volume of vector data transferred and improving tile rendering performance.
Syntax
GEOMETRY ST_AsMVTGeomEx(
GEOMETRY geom,
BOX2D bounds,
INTEGER res_prec=1,
INTEGER extent=4096,
INTEGER buffer=256,
BOOLEAN clip_geom=true
);Parameters
geom The geometry object to convert.
bounds The rectangular boundaries of the tile, excluding the buffer.
res_prec The minimum pixel threshold for rendering. Geometry objects whose maximum pixel span in the x-axis or y-axis falls below this value are filtered out. Default value: 1.
extent The tile size in the tile coordinate system. Default value: 4096.
buffer The buffer size in the tile coordinate system. Default value: 256.
clip_geom Specifies whether to clip geometry objects at tile boundaries. Default value: true.
Usage notes
- This function is designed for vector data of varying sizes. It is not suitable for point data.
- For small tiles, setting
res_precto a large value may cause many vectors to become invisible.
Example
Filter out geometry objects that span fewer than two pixels in the x-axis or y-axis of the current tile before generating the MVT output:
-- Only vectors spanning at least two pixels in the x-axis or y-axis are included.
WITH mvtgeom AS (
SELECT ST_AsMVTGeomEx(
geom,
ST_Transform(ST_TileEnvelope(0, 0, 0), 4326),
2
) AS geom
FROM geom_table
WHERE geom && ST_Transform(ST_TileEnvelope(0, 0, 0), 4326)
)
SELECT ST_AsMVT(mvtgeom.*);