[postgis-devel] ST_AsMVT
Paul Norman
penorman at mac.com
Fri Sep 16 14:35:50 PDT 2016
On 9/16/2016 4:27 AM, Björn Harrtell wrote:
> CREATE FUNCTION ST_AsMVT(query text, extent box2d, resolution double,
> buffer integer, pixelratio integer)
As an interface I propose taking in a row or similar instead of a query.
Anything that takes SQL as text can be a problem.
For the other parameters I recommend name text, bounds box2d, extent
integer DEFAULT 4096, buffer integer DEFAULT 0, clip_geoms bool DEFAULT
true.
name is the required name of the layer.
bounds is the area which corresponds to the unbuffered area of the
vector tile, and will typically be the area of an xyz tile.
Extent is the extent for the vector tile, as specified in the spec.
Buffer is how far to go out for geometries to include as well as used in
clipping.
clip_geoms is if geometries should be clipped at the buffered extent or
not. It's valid to include a geom that goes beyond the buffered extent,
but this is not normally done for rendering.
For a return type, I'd go with bytea, being the binary data for the
layer. Don't apply gzip compression, it's not part of the vector tile
itself.
Thanks to the properties of mapbox vector tiles, you can then build a
multi-layer tile by concatenating the results of multiple ST_AsMVT calls
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