Math question: How to compute the area of polygons

[Dar Scott]

On Tuesday, March 18, 2003, at 02:06 AM, Malte Brill wrote:

> I want to extract all lines of 2 polygons by analysing their points,
> evaluate the area of each of them with some magic formula I don´t know 
> ;-)

Figure out how to get the area of a triangle.  Then come up with a way 
to methodically break up a polygon into triangles.  Add up the areas of 
those.

> and to figure out the area of the smallest polygon surrounding both of 
> them.

Do you mean a smallest polygon that contains exactly the union of the 
points in the two polygons?  (If the polygons do not overlap this might 
include a thin bridge with no area.)

Or do you mean the smallest _convex_ polygon such that all points in 
the two polygons are in the generated polygon?  (By convex, I mean all 
angles at corners are <= 180 degrees, that there are no "dents" in the 
sides.)

Dar Scott