added new sanity-check assertions

fixed issue with angles [bad interface]
- adjusted other parts accordingly
- added corresponding test-cases
started working on absolute heading

geo/Angle.h

@@ -29,6 +29,13 @@ public:
 		return radToDeg(getRAD_2PI(x1,y1,x2,y2));
 	}
 
+	/** ensure the given radians-value is within [0:2pi] */
+	static float makeSafe_2PI(float rad) {
+		while(rad < 0) {rad += 2*PI;}
+		while(rad >= 2*PI) {rad -= 2*PI;}
+		return rad;
+	}
+
 
 	/**
 	 * gets the angular difference between
@@ -44,13 +51,14 @@ public:
 
 	/**
 	 * gets the angular difference between
+	 * "angular change from r1 to r2"
 	 * - the given radians [0:2PI]
 	 * - as a change-in-direction between [-PI:+PI]
 	 */
 	static float getSignedDiffRAD_2PI(const float r1, const float r2) {
 		Assert::isBetween(r1, 0.0f, (float)(2*PI), "r1 out of bounds");				// [0:360] deg
 		Assert::isBetween(r2, 0.0f, (float)(2*PI), "r2 out of bounds");				// [0:360] deg
-		float diff = r1-r2;
+		float diff = r2-r1;
 		if		(diff > +PI) {diff = -(2*PI - diff);}
 		else if	(diff < -PI) {diff = +(2*PI + diff);}
 		Assert::isBetween(diff, -PI, (float)(+PI), "result out of bounds");	// [-180:+180] deg

geo/Heading.h

@@ -33,8 +33,11 @@ public:
 	}
 
 	/** signled angular difference [-PI:+PI] */
-	float getSignedDiff(const Heading other) const {
-		return Angle::getSignedDiffRAD_2PI(rad, other.rad);
+//	float getSignedDiff(const Heading other) const {
+//		return Angle::getSignedDiffRAD_2PI(other.rad, rad);
+//	}
+	static float getSignedDiff(const Heading from, const Heading to) {
+		return Angle::getSignedDiffRAD_2PI(from.rad, to.rad);
 	}
 
 	/** update the angle but ensure we stay within [0:2PI] */