[postgis-devel] Proposal: Adding buffer parameter to ST_TileEnvelope()

[Yuri Astrakhan]

Paul, I was thinking of using the same definitions as in ST_AsMVTGeom():

* buffer is the buffer distance in tile coordinate space to optionally clip
geometries.

So the buffer would be in the tile's units, and depend on the zoom level.
I suspect we have to add extent parameter too, rather than use default 4096.


On Wed, Nov 13, 2019 at 9:14 AM Paul Ramsey <pramsey at cleverelephant.ca>
wrote:

> Buffer in what units?
> Would you really buffer, say, a tile that is a quarter of the earth, by
> 100 meters? Buffering tiles is to make rendering work better, so the
> buffers will be relative to the expected widest applied style/marker.
> If in “pixels”, what would be the expected number of pixels in a tile? In
> proportion of the tile? 1/10 of a tile? 1/20?
> P.
>
> > On Nov 13, 2019, at 12:06 AM, Yuri Astrakhan <yuriastrakhan at gmail.com>
> wrote:
> >
> > Would it make sense to add a `buffer` parameter to ST_TileEnvelope(),
> similar to ST_AsMVTGeom() ?
> >
> > To my understanding, ST_TileEnvelope common use case is to create a bbox
> filter -- to get just the relevant data before packaging it with
> ST_AsMVT().  This works well for the line and polygon geometries, but when
> dealing with point data, e.g. city names, one has to increase that bbox by
> a significant margin (e.g. half of the tile size) in order to capture
> labels from the neighboring tiles and prevent label clipping.
> >
> > I think this use case is common enough to add buffer parameter to
> ST_TileEnvelope - where it would increase the bbox size by the the given
> distance in tile coordinate space.
> >
> > Proposed additional signature:
> >
> > geometry ST_TileEnvelope(integer tileZoom, integer tileX, integer tileY,
> integer buffer=0, geometry bounds=...);
> >
> > (Would existing method signature without the buffer param conflict if
> the buffer is added before the existing bounds param? They are of different
> type.)
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