Affine transformation functions

[Mike Taves]

This is a feature request to apply a 2D or 3D affine transformation to a geometry. The routine should ideally be applied in-place, only changing the values of the vertices.

There are several implementations of the affine transform, including ​shapely.affinity and PostGIS (e.g. ​here and ​here).

Derived functions, such as "rotate", "scale", "transform" and "skew" can be build by client applications by assembling the appropriate matrix parameters. As for the function signature, I think the best approach would be to keep the same matrix order of [a, b, d, e, xoff, yoff] for 2D and [a, b, c, d, e, f, g, h, i, xoff, yoff, zoff] for 3D. Whether or not these should be fed into a single function as either a 6 or 12-length double array, or as two functions with fixed arguments is debatable.

[Mike Taves]

And of course there is a ​JTS AffineTransformation Class, which seems the ideal way to define how this should be defined in GEOS.

[strk]

This might help QGIS handling of rotation: ​http://hub.qgis.org/issues/11814

[mloskot]

@mwtoews Grab JTS sources and start scratching re-write of their AffineTransformationBuilder from Java to C++

​https://gist.github.com/guziy/1356654/75434783be64cd35a72d540ec244d8de4d13554d

Submit a patch against trunk, even if half-baked implementation then we can continue improving it.

[robe]

Milestone renamed