[postgis-devel] ST_AsMVT

[Björn Harrtell]

2016-09-17 17:09 GMT+02:00 Sandro Santilli <strk at kbt.io>:

> On Sat, Sep 17, 2016 at 04:25:06PM +0200, Björn Harrtell wrote:
>
> > Found https://github.com/mapbox/vector-tile-spec/issues/11 supporting
> the
> > claim that a multi-layered vector tile is indeed a set of independent
> layer
> > messages. Still not sure about the possibility of aggregating the
> contents
> > of a layer as separate calls.
>
> If I recall correctly, a good reason to have all the data at once
> before starting to encode it was the indexing of values.
>
> That is, attribute _values_ can be put in a dictionary and only
> referenced per-feature (think of a palette for graphics).
> Such "dictionary" can help in case of large repeated values.
>
> Using a row-by-row approach, makes it impossible to build such
> dictionary, which is why my early attemps were just at producing
> the geometric part, very much like the GML output works, delegating
> composition of the whole final product to the caller (which could
> eventually also be a ROW-taking wrapper).
>

Thanks for this insight. I've still not reached a good enough understanding
of what is and what is not possible/practical regarding protobuf binary
(packed message) composition so will have to do more research.

As a side note, while trying to increase my knowledge about protobuf I've
also looked at flatbuffers and wonder if it wouldn't be the better
alternative for future spatial formats. Lightning talk at
https://www.youtube.com/watch?v=olmL1fUnQAQ by Wouter van Oortmerssen who
is to blame for getting me into programming in the first place by creating
the now ancient language Amiga E. :)

--strk;
>
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