> > Once the plane is known, the points are translated to the > > coordinate system of the plane, their Z coordinates are ignored > > or dropped, and this becomes a 2-dimensional area calculation. > > That's exactly what I suggested :)
Hmm - I guess I didn't read that far...
> You haven't said whether the ordering of the points around the > loop is given or not.
The user will specify the markers to be used (there are other markers on the heart which will not be involved in this ring). A routine will identify the order by picking one point and then determine which of the remaining points is closest, and will piece-wise work it's way around the ring. This should avoid any errors if the user gives the order incorrectly.
> Also, what do you want to do if the loop is not convex?
Do you mean what if the loop looks like a potato chip with a bite taken out of it?
I don't see how that would affect the proposed area calculation method.