[postgis-devel] ST_AsMVT

[Björn Harrtell]

2016-09-16 23:35 GMT+02:00 Paul Norman <penorman at mac.com>:

>
> 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
>

Thanks Paul, I thought the first Paul was messing with me but now I see he
was serious. :) To clarify, I understand that SQL as text is a problem I
was just not seeing any alternative.

I think your recommendations for the other parameters make sense.

I was unaware of the possibility to concatenate layers in binary format, it
seems reasonable but need to investigate further. I'm still confused about
using a "row or similar" type instead of a query, if by that you mean to
encode just a single geometry at a time, because I can't see how that could
be possible to concatenate as binary. Perhaps my confusion can be explained
by that I also have problems understanding the "40.3.4. Row Types" chapter
in the PostgreSQL documentation.


>
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