[postgis-devel] Deprecate ST_MapAlgebraExpr and ST_MapAlgebraFct

Pierre Racine Pierre.Racine at sbf.ulaval.ca
Wed Oct 10 15:32:16 PDT 2012

> As for removing expression-based map algebra, historical testing showed
> that performance of callback functions was consistently faster than
> expressions (even with use of prepared statements).  Not to mention the
> ease of debugging a function rather than an expression where the problem
> could be in the user's expression or how that expression is parsed.

Speed is not always the deciding feature...

That means no support for people not comfortable with writing a custom function...

There are also a bunch of function dependent on the expr variant: 

-ST_Intersection(raster, raster)
-ST_Clip(raster, geom),

It is now the most efficient way (that I know) to change the pixel type of a band:

ST_MapAlgebraExpr(rast, '32BF', '[rast]') rast

When I consider all the easy things I can do with the expr variant and I think about the dozens of custom functions I will have to write... I guess we will have to provide many basic ones. And maintain them...


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