vector3.angleTo with vec on (0,0,0) returns NaN

I noticed that vector3.angleTo() returns NaN when either the vector on which it’s called or the target vector is at the origin (0,0,0).

let vec1 = new THREE.Vector3( -2, 2, 0 );
let vec2 = new THREE.Vector3( 0, 0, 0 );

console.log( vec2.angleTo(vec1) );   // NaN
console.log( vec1.angleTo(vec2) );   // NaN

Three.js version : r108 Browser : Chrome OS : Windows

[Mugen87]

@felixmariotto You are right, this behavior is unfortunate. I suggest the same what Unity does in Vector3.Angle. Vector3.angleTo() would look like so then:

angleTo: function ( v ) {

	var denominator = Math.sqrt( this.lengthSq() * v.lengthSq() );

	if ( denominator === 0 ) return 0;

	var theta = this.dot( v ) / denominator;

	// clamp, to handle numerical problems

	return Math.acos( _Math.clamp( theta, - 1, 1 ) );

}

[saschandroid]

As the user has to deal with valid inputs anways (test for non-zero vectors), wouldn’t it be better to just return π/2 radians (90°) instead of a console.error? Returning π/2 seems for me to be mathematical correct … Wikipedia: “In Euclidean space, two vectors are orthogonal if and only if their dot product is zero, i.e. they make an angle of 90° (π/2 radians), or one of the vectors is zero.” (https://en.wikipedia.org/wiki/Orthogonality). Wikibooks: “the angle between the zero vector and any other vector is defined to be a right angle” (https://en.wikibooks.org/wiki/Linear_Algebra/Length_and_Angle_Measures). Returning (mathematically wrong) NaN (and conole.error) because the user should not try to calculate the angle to/from a zero-vector doesn’t look like a good solution for me.

Users would then only have to check for zero-vectors if the returned angle is exactly π/2 and only if this is relevant later on.

By the way: I use “angleTo” while calculating weighted (angle and surface) vertex normals. That worked perfectly fine because I had to test the angle to be in a certain range anyways. After updating three.js I got thousands of console.errors, so I now have to test every (calculated) vector to be non-zero before using “angleTo”.