Tweak gibs

src/Quaternion.hs

@@ -1,9 +1,12 @@
 module Quaternion
     ( rotateToZ
+    , vToQuat
+    , module Linear.Quaternion
     ) where
 import Geometry.Data
 import Geometry.Vector3D
 import qualified Linear.Quaternion as Q
+import Linear.Quaternion
 
 -- apply a rotation as if the z axis moves to the new point.
 rotateToZ :: Point3 -> Point3 -> Point3
@@ -12,3 +15,10 @@ rotateToZ z1
     | otherwise = Q.rotate $ Q.axisAngle cprod (angleVV3 z1 (V3 0 0 1))
   where
     cprod = crossProd z1 (V3 0 0 1)
+
+vToQuat :: Point3 -> Point3 -> Q.Quaternion Float
+vToQuat a b 
+    | cprod == V3 0 0 0 = Q.axisAngle (V3 0 0 1) 0
+    | otherwise = Q.axisAngle cprod (angleVV3 a b)
+  where
+    cprod = crossProd a b