Hi Nuno,
2017-08-30 16:25 GMT+02:00 Nuno Oliveira <[email protected]>:
> Hi Mauro,
>
> When you say AggregationFunctions enum you mean this one:
> https://github.com/nmco/geotools/blob/917d43efca4a920ec3153304d64488
> 3101ca3921/modules/library/main/src/main/java/org/
> geotools/feature/visitor/Aggregate.java
>
Yes, that one, in addition to this one:
https://github.com/geotools/geotools/blob/82543fe0d3cee7f20b022f39b2bdae56fd5ba5bd/modules/unsupported/process-feature/src/main/java/org/geotools/process/vector/AggregateProcess.java#L47
> One thing is not clear to me, will this computation by delegate the
> underling data store when possible ?
> For example this aggregation can be done like this in Postgis (using some
> OSM data as an example):
>
> SELECT admin_level, SUM(ST_AREA(geometry))
> FROM public_osm_administrative_version_log
> GROUP BY admin_level;
>
>
I am currently working on getting the optimization done. There are some
obstacles, but I am trying to work-around them. That's exactly the SQL I
would like to produce.
> Since the aggregate attribute is an *Expression*:
> https://github.com/nmco/geotools/blob/917d43efca4a920ec3153304d64488
> 3101ca3921/modules/library/main/src/main/java/org/
> geotools/feature/visitor/GroupByVisitorBuilder.java#L37
>
> I guess the attribute can be encoded as a function call and the SUM
> aggregation used to compute the aggregation.
>
> So will the new Area function be a composition of SUM aggregation function
> and the a geometry are function or a
> competently standalone thing ?
>
My current implementation is using a standalone visitor that is doing both
things at once. In the end what I need is a SumArea aggregate, since Area
by itself is not really an aggregate.
--
Regards,
Mauro Bartolomeoli
==
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