[postgis-devel] ST_AsMVT

[Paul Norman]

On 9/17/2016 8:09 AM, Sandro Santilli wrote:
> On Sat, Sep 17, 2016 at 04:25:06PM +0200, Björn Harrtell wrote:
>
>> >Foundhttps://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).

You're right. Joining different layers is fine, but each layer has some 
common information that is needed.

Should it be an aggregate function then?


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