[raster] ST_AsRaster aggregate function

[robe]

Pierre,

Not sure if this is what you had in mind when you said "Burn In" function in your talk. A common need I have which I am sure is that of many BI analysts is the need to show simple thematic maps in reports.

What came to mind to me was an aggregate ​ST_AsRaster function that takes a set of geomval rows (or multicolumn geom, value) and builds a raster. Basically a reverse of the ​ST_DumpAsPolgons function.

This would make it trivial to do a query such as

SELECT ST_AsPNG(ST_AsRaster(gval),300,300) As mymap
FROM (SELECT ROW(ST_Union(geom), SUM(pop))::geomval As gval
FROM sumregion
GROUP BY region_name) As foo;

Which is big considering many report writers allow their picture box controls to be bound to query fields. We might have a new crowd of BI analysts looking to get a piece of PostGIS action.

[pracine]

This is ST_UnionToRaster as planned in Objective FV.19 of the future specs:

http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking03

It is dependent on the two raster version of ST_Mapalgebra which is being developed.

[robe]

Milestone renamed

[strk]

FV.19 signature of ST_BurnToRaster seems to be missing a band argument, also it recommends using ST_AsRaster(geometry, rast, value, 'CROP') but I don't see any signature like that existing ?

What's the policy on updating that specification ?

[strk]

WIP: ​https://git.osgeo.org/gitea/postgis/postgis/pulls/232

[strk]

I'll keep PR-232 for ST_BurnToRaster (as per FV.19) but for this ticket's goal I'll use another PR to wrap ST_Union (raster version) so the aggregate is faster. This matches the original request by Regina.

[strk]

Comments welcome on this proposed interface for the aggregate:

raster ST_AsRasterAgg(
  geomval set,
  raster ref,
  text pixeltype,
  double precision nodataval=0,
  text uniontype='LAST',
  bool touched=false
);

[robe]

that works for me.

[strk]

WIP PR: ​https://git.osgeo.org/gitea/postgis/postgis/pulls/234

[strk]

I'm not sure I like "geomval" single argument rather than two distinct "geom" and "val" arguments, I don't see the benefit of that…

[strk]

I went with the extended version:

ST_AsRasterAgg(
 geom geometry,
 val float8,
 ref raster,
 pixeltype text,
 nodataval float8,
 uniontype text,
 touched boolean
)

The aggregate burns each incoming geometry to a raster having the origin and scale specified by the reference raster and unions it to the state raster using the specified uniontype.

If we all agree on the signature I'll proceed with documentation

[strk]

Well I went ahead and wrote documentation too: ​https://git.osgeo.org/gitea/postgis/postgis/pulls/234

[Sandro Santilli <strk@…>]

In 2b7380ec/git:

Add ST_AsRasterAgg aggregate

Closes #1247
Includes regress test and documentation