[fdo-internals] Updated RFC 11 - Area and Length functions

[Orest Halustchak]

Hi,

Based on the feedback to RFC 11, the RFC has been updated.
	
http://trac.osgeo.org/fdo/wiki/FDORfc11

>From the discussion, we kept the 2D requirement but made it clearer that
Z is skipped in the calculation. We could add separate 3d functions at a
future date.

The main change is for geodetic data. The RFC now calls for a ground
distance or area in metres or square-metres to be returned using a
calculation based on "general accepted formulae". For providers that do
not have a native coordinate system library, our intention is to reuse
code from proj4 for the length calculation and also to adapt it for an
area calculation. We will post these functions as fdo common utilities
so that other provider writers can use them as well if they choose.

Thanks,
Orest.