Where something rests on a model is the highest point under its footprint, not the hit of a ray through its centre

Fact

A thing set down on a model — a bird on a head, a hat on hair, a prop on a shelf — rests on the highest point under its whole footprint. One ray cast down through its centre measures something else: on any top with gaps (spiky hair, curls, two leaves either side of a stem) the centre ray falls into a gap and reads low, by a good share of the feature's height.

Why it matters

Attachment heights are usually tuned by eye once and stored as constants, then drift as the models change; the drift shows only as a prop sunk into, or hovering over, one combination out of dozens. Calibrating them with a centre ray fails the other way: the number looks precise and puts the prop inside the spikes.

How to apply

• Sample a disc of rays the radius of the resting thing's footprint (a ring or two of 8–12 rays, plus the centre) and take the highest hit.
• Size the disc to the footprint, not larger: a wider one picks up what the thing sits beside rather than on, such as a bow at the side of a head.
• Keep stored heights honest with a test over every combination of model, accessory and style. In three.js, Raycaster.intersectObject works headlessly in Node with no WebGL context, so assert 0 <= stored - measured <= tolerance for each one.
• Exclude by name what the thing is known to sit beside, so the test stays strict for everything else.