[postgis-devel] Deprecate ST_MapAlgebraExpr and ST_MapAlgebraFct

[dustymugs]

Hey all,

I'm planning on committing support for n-raster (and n-band) map algebra
as ST_MapAlgebra().  This new map algebra function only works on
user-specified callback functions as trying to support an
expression-based n-raster with neighborhood would be extremely
cumbersome.  Think of the number of keywords required if you have
variable size neighborhoods and unlimited number of rasters and bands...

I'd like to deprecate all variants of ST_MapAlgebraExpr,
ST_MapAlgebraFct and ST_MapAlgebraFctNgb in 2.1 with eventual removal in
2.2.  The use of Expr, Fct, FctNgb suffixes is tedious and the variants
for 1 raster and 2 rasters is confusing for users and horrible to
maintain in the codebase.

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.

This simplification unifies everything and keeps things simple and stupid.

Thoughts?

-bborie

PS: Before anyone goes nuts, I don't plan on replacing the existing code
for Expr, Fct and FctNgb variants.  I'm only adding ST_MapAlgebra() for
2.1.  The Expr, Fct and FctNgb variants will be removed in 2.2.