[postgis-devel] ST_AsMVT

Björn Harrtell bjorn.harrtell at gmail.com
Sun Sep 18 15:22:23 PDT 2016


2016-09-18 17:28 GMT+02:00 Paul Ramsey <pramsey at cleverelephant.ca>:

> I think that “pass in a SQL” string, or “table name” are the roads to
> hackyland. You’re building a database: take in and emit primitive
> values/objects or tuples or tuplesets. You build primitives and let other
> folks build the SQL stuff on top.
>

Agreed.

I got my hands dirty concatenating encoded protocol buffer messages and
fields. Finally I think the wire format have sinked in with me.

I see now that it should be possible to not only binary concatenate layers
into a tile but also features into a layer message. I have a feeling I'm
late to the party in understanding this, but I guess better late than never.

I'll be back if I survive the trip deeper into PostgreSQL.

/Björn


> P.
>
>
> On Sep 18, 2016, at 8:24 AM, Björn Harrtell <bjorn.harrtell at gmail.com>
> wrote:
>
> 2016-09-18 7:48 GMT+02:00 Sandro Santilli <strk at kbt.io>:
>
>> On Sat, Sep 17, 2016 at 05:47:39PM -0700, Paul Norman wrote:
>> > On 9/17/2016 8:09 AM, Sandro Santilli wrote:
>>
>> > >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?
>>
>> Probably, which means you'd also need to define a type
>> to represent the state (including the dictionary, for example).
>> It's enough stuff that might be better to move into its own
>> extension.
>>
>
> What do you think about the alternative of simply supplying the function
> with a name of a table or view assuming the the proposed structure then
> dynamically query it internally using the supplied bounds?
>
>
>>
>> --strk;
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