Simple four-point NURBS Curve is interpreted badly.

[msimpson]

Description

A NURBS curve is being interpreted badly by the FBXLoader.

The curve is a simple four-point diamond:

Geometry: 1714157613440, "Geometry::", "NurbsCurve" {
	GeometryVersion: 124
	Type: "NurbsCurve"
	NurbsCurveVersion: 100
	Order: 2
	Dimension: 3
	Form: "Closed"
	Rational: 0
	Points: *16 {
		a: 857.9216016,0,-0,1,0,0,-857.9216016,1,-857.9216016,0,-0,1,0,0,857.9216016,1
	} 
	KnotVector: *7 {
		a: 1,1,2,3,4,5,5
	} 
}

However, the intermediate points in the resulting Line geometry are off near the corners (see below).

Assuming @looeee can help/advise.

EDIT

FYI, this was exported from C4D.

So I'll understand if NURBSCurve is being misled by something with the knots, etc. and it's not Three's fault.

To Reproduce

Load the following FBX (diamond.zip) in the three.js editor.

Note that you'll need to scale down quite a lot (0.005 or more) as it was pulled from a separate scene.

Platform:

• Device: Any
• OS: Any
• Browser: Any
• Three.js version: r130

[WestLangley]

This code block is a bit verbose.

three.js/examples/jsm/loaders/FBXLoader.js

Lines 2298 to 2309 in e0000ac

	const vertices = curve.getPoints( controlPoints.length * 7 );
	const positions = new Float32Array( vertices.length * 3 );
	vertices.forEach( function ( vertex, i ) {
	vertex.toArray( positions, i * 3 );
	} );
	const geometry = new BufferGeometry();
	geometry.setAttribute( 'position', new BufferAttribute( positions, 3 ) );

It can be rewritten as

const geometry = new BufferGeometry();
geometry.setFromPoints( curve.getPoints( controlPoints.length * 7 ) );

A reasonable guess is controlPoints.length * 7 is not enough to accurately represent the curve in this case.

[msimpson]

Thanks!