From: Scott Worley <ScottWorley@ScottWorley.com>
Date: Mon, 31 Dec 2012 06:56:34 +0000 (-0800)
Subject: Explicitly bounds-check in angle_between()
X-Git-Url: http://git.scottworley.com/nt3d/commitdiff_plain/72eac64d07af484314745fd0e9466e0f94915684?hp=9ff1b1e6e6409df1fd67ed486b21033ddb39273f

Explicitly bounds-check in angle_between()

This avoids introducing NaNs due to numerical error while measuring
extreme angles -- angles near 0 or pi radians.
---

diff --git a/nt3d.js b/nt3d.js
index 9eee504..0389946 100644
--- a/nt3d.js
+++ b/nt3d.js
@@ -259,7 +259,14 @@ nt3d = {
 		        point[2] + offset[2]];
 	},
 	angle_between: function(a, b) { // a and b must be unit vectors
-		return Math.acos(this.dot(a, b));
+		var the_dot = this.dot(a, b);
+		if (the_dot <= -1) {
+			return Math.PI;
+		}
+		if (the_dot >= 1) {
+			return 0;
+		}
+		return Math.acos(the_dot);
 	},
 	rotate_about_origin: function(points, axis, angle) { // axis must be a unit vector
 		// From http://inside.mines.edu/~gmurray/ArbitraryAxisRotation/