[surface] getArea(point cloud segment)

Is your feature request related to a problem? Please describe.

I am developing segmentation algorithms in which I need to calculate the area of segments to make selections and I think the implementation of area calculation i did works well and can be applied general purpouse, so it could be merged in PCL

Solution

Essentially there are a few steps:
(1) optional voxeling of the segment
(2) NormalEstimationOMP
(3) GreedyProjectionTriangulation
(4) Sum the area of greedy triangles
Loop: area += 0.5 * P.cross(Q).norm();
where P and Q are two vectorial sides of the triangles

Describe alternatives you've considered

one might consider alternative surface mesh/triangulations but this seems to work fine on the samples I tested it
there is a little are overestimate due to the fact that the mesh is not perfectly smooth. the voxeling is aimed at reducing this effect.

the area += loop is done as double

An alternative would be to extract optionally this info directly inside the greedy alg. as it comes available so to minimnize the total processing time

Start by reviewing the NormalEstimationOMP and GreedyProjectionTriangulation steps described in the issue, along with the proposed voxelization and triangle-area loop. Clarify where a general-purpose segment-area capability belongs and how the alternative of calculating it inside the greedy algorithm should be evaluated; done requires an agreed scope and validation on representative point-cloud segments.