Hi,

2014-01-29 Jon Summers <j.summers@la-solutions.co.uk>

My application uses a 3D coordinate system. I want to compute a normal for a model such as a ring. I don’t see a property or algorithm that provides computation of a normal. Have I missed something in my searches?

A ring would have to be planar to compute a normal, so a related question is “If dimensionality is greater than 2, how do I determine that a model is planar?”

Guys, correct me if I'm wrong.

Currently 3D functionality is very limited. Some functions doesn't work for 3D geometries and some silently assume that the third coordinate is equal to 0. In particular, there is no function calculating the normal, checking if all points are lying on some plane, etc.

So you'd be forced to calculate the normal by yourself. You probably would like to do something like this:
1. find two nonparallel segments, and calculate the cross product (the orientation of a polygon is known)
2. if needed, calculate the last component of the plane equation and check if all points are lying on the same plane (WRT some EPS).
right?
Using pure BG funcionality you'd be forced to store your normal as a point (BG has no Vector concept). For vector/points operations you could use non-official functions from boost/geometry/arithmetic.
Alternatively, you could also use e.g. QVM (http://www.revergestudios.com/boost-qvm/) but it isn't a part of Boost yet.

Regards,
Adam