ProjectionManager: Math.atan used where Math.tan is required — ortho view ~16 % too small at fov 60, error scales with fov

[stokuewe]

Versions

@thatopen/components 3.4.8 (verified against the published dist/index.mjs; source: packages/core/src/core/OrthoPerspectiveCamera/src/projections.ts).

What happens

getPerspectiveDims() computes:

const height = depth * 2 * Math.atan((camera.fov * (Math.PI / 180)) / 2);

and getDistance() uses the same inverted form backwards. The half-height of a perspective frustum at distance d is d * tan(fov/2), not d * atan(fov/2).

Numbers

• fov 60: 2·atan(0.5236) = 0.9647 vs 2·tan(0.5236) = 1.1547 → factor 0.8354, i.e. the ortho view shows 16.5 % less height than the perspective view it replaces.
• fov 50: factor 0.8826 (−11.7 %).
• The error vanishes as fov → 0 (atan(x) ≈ tan(x) ≈ x) — strong evidence of a typo rather than intent, since the switch is only size-consistent for narrow FOVs.

Visible symptom

Every perspective→ortho toggle zooms IN slightly; because getDistance() inverts with the same wrong function, round-tripping with matchOrthoDistanceEnabled compounds the error.

Suggested fix

Replace Math.atan with Math.tan in both methods.