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

[Paul Ramsey]

> On Nov 13, 2019, at 8:22 AM, Yuri Astrakhan <yuriastrakhan at gmail.com> wrote:
> 
> 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.

Yeah, that’s what I thought… it gets uglier and uglier, no?


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