

Shoelace Formula - Someone
http://en.wikipedia.org/wiki/Shoelace_formula

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silentvoice
Very handy formula. I was recently in the situation of being given a bunch of
polygons, each represented in a list-of-edges format and I needed to compute
the outward-pointing normals for the edges. It's relatively straightforward to
translate list-of-edges into list-of-vertices, but not so straightforward (to
me) to ensure that the vertices are in counterclockwise order after this
translation.

If you take the shoelace formula and remove the absolute value then you still
get the correct area up to floating point errors, just there may be a minus
sign in front of it. If there is a minus sign, reverse the order of your
vertices and boom you have counterclockwise order. Computing the normals after
this is routine.

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robinhoodexe
Sort of unrelated: reading Wikipedias mobile pages on a "standard" (15" in my
case) screen is actually rather nice. Very clean look.

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percept
Oh, that is nice--think I'll start heading there by default
([https://en.m.wikipedia.org/wiki/Main_Page](https://en.m.wikipedia.org/wiki/Main_Page)).

