Any Surveyors?

[Peter Murphy]

Hi Jacob,

Thanks for your detailed reply in Post #13.

I immediately recognized your command sequence DUP HEAD SWAP TAIL SWAP +, presumably operating on lists of X and Y coordinates, because I use that very sequence on a list of [X Y] vectors. Then, where you use *, and I use CROSS.

This method has a long history, reaching back to Gauss and even earlier:

<http://en.wikipedia.org/wiki/Polygon>

It's nice to have confirmation that it really is a Surveyor's formula.