[gdal-dev] Support for measures

[Ari Jolma]

Folks,

I'd like to try to implement the XYZM support since I have some free time.

Before making a RFC, there are some thoughts/questions/ideas:

* I made a fork for this work at https://github.com/ajolma/GDAL-XYZM so 
I can more easily use travis.

* I think this is mainly changes in the geometry API and generic methods.

Are there other drivers than shape, which are affected? Currently shape 
driver creates XYZ data from XYM data, that would change, which may 
break some code.

* Currently XYM or XYZM data seems to be accepted (by WKT and WKB 
importers for example) but not stored in generic objects.

* The closeness of XYZ and XYM might need some thought:

For example C++ API for making a adding a XYZ and XYM point to a curve 
would be the same. Currently the method calls Make3D() if the curve is 
2D, which is not ok for XYM data.

Tickets related to this are

https://trac.osgeo.org/gdal/ticket/6063
https://trac.osgeo.org/gdal/ticket/6331

Are there other things I should know?

The target would be 2.1 I guess.

Ari