Raycaster Normal Incorrect for Scaled Mesh

Questions
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1

Hi, all. I’m having some trouble getting the correct normal of a face intersected by a ray when the mesh has been scaled and am hoping someone can point out what I’m doing wrong.

Here’s a demo: https://codepen.io/macapam689/pen/abbMxGV?editors=0010

The intersect normal is correct for the left hand cylinder, which has not been scaled, but is incorrect for the right hand cylinder which has been scaled in the x axis.

As a side question, when calling computeVertexNormals() on the geometry, the results are odd. You can see this by setting the COMPUTE_VERTEX_NORMALS boolean in the example. Interestingly, the normals for the top vertices of the right hand cylinder point in the direction I would expect the intersect face normal to point.

I’m sure it’s probably something basic but I can’t find the magic combination of search terms to find the answer. Thanks to anyone who can help figure this out.

2

The normalMatrix has to be calculated from the worldMatrix before it can be applied:

const normalMatrix = new Matrix3().getNormalMatrix( obj.matrixWorld );
normal.applyMatrix3( normalMatrix ).normalize();

Updated pen: https://codepen.io/MekonLips/pen/dyyBJEV?editors=0010