How to calculate area of an irregular polygon by 3D coordinates?

[Jason_Steven]

I have an array with a set of points(x,y,z coordinates),and the number of points in an irregular polygon.How do I calculate the surface area of this closed polygon?

[m_k]

Check measure tool (or was it measure tool NG?) in the SVN repository - I think it has some function to measure area (it may also have the code to move polygon vertices)

[mayra]

You would probably be better off asking these kind of questions (ie: general directX/algorithm, not WW specific) in a more general forum, where there is a larger user base.

[patmurris]

You will probably need to tessellate or triangulate your polygon first, and then compute the sum of all the triangles area. However, if your points are not coplanar you'll have trouble doing so.

Are you trying to measure some terrain area?

[Jason_Steven]

Originally Posted by patmurris

You will probably need to tessellate or triangulate your polygon first, and then compute the sum of all the triangles area. However, if your points are not coplanar you'll have trouble doing so.

Are you trying to measure some terrain area?

First,thank you very much!
Yes,These points may be not coplanar.I am trying to measure some terrain area!I just downloaded the lastest code by SVN.It supplied an algorithm about irregular polygon area,but I doubt it a bit.

[patmurris]

Maybe it will be easier to convert you cartesian points to lat-lon pairs and consider your polygon on a 'flat' projection like sinusoidal which is equal area. That would allow to compute the projected area (the one you would measure on a map). If you are looking for the 'real' surface area taking into account the terrain slopes, then things will be a tad more involved.

[m_k]

BTW Pat, how this kind of area computation is (will be) done in WWJ 0.6?

[patmurris]

Originally Posted by m_k

BTW Pat, how this kind of area computation is (will be) done in WWJ 0.6?

Pretty much as i describe above.

For projected area the polygon is tessellated and each triangle area is computed in a sinusoidal projection.

For 'real' surface area an approximation is computed using a sampling grid and an overall slope factor for each cell that is 'inside' the ploygon. Note that real area is a very fishy concept due to the fractal nature of terrain and the limited resolution of elevation data. After trying out quite a few methods, the sampling grid is an acceptable approach - and not too slow. Use cases for such area are very few though.

[Jason_Steven]

Can anyone supply some source code about it?
Thank you very much!
I don't know that how to triangulate a irregular polygon and calculate the area of each triangle inside this polygon.
It's very urgent.
Thank you very much again!