Work on crab feet

src/Geometry/Vector.hs

@@ -67,6 +67,12 @@ angleVV a b
             d = a `dotV` b
          in acos $ d / (ma * mb)
 
+-- returns the angle opposite length a
+angleThreeSides :: Float -> Float -> Float -> Float
+angleThreeSides a b c = acos $ (f b + f c - f a) / (2*b*c)
+  where
+    f = (^ (2 ::Int))
+
 -- | Safe version of 'angleVV' that returns 0 if either vector is null.
 safeAngleVV :: Point2 -> Point2 -> Float
 {-# INLINE safeAngleVV #-}

src/Geometry/Vector3D.hs

@@ -1,6 +1,7 @@
 {-# LANGUAGE BangPatterns #-}
 module Geometry.Vector3D
     where
+import Linear
 import Geometry.Vector
 import Geometry.Data
 
@@ -121,7 +122,7 @@ dotV3 (V3 x y z) (V3 a b c) = x*a + y*b + z*c
 
 angleVV3 :: Point3 -> Point3 -> Float
 angleVV3 a b 
-    | a == b = 0
+    | a == b || norm a == 0 || norm b == 0 = 0
     | otherwise = acos $ dotV3 a b / (magV3 a * magV3 b)
 
 --projV3 :: Point3 -> Point3 -> Point3