FA-70190 / Map projection transforms / Member archive

Orthographic globe view with back-side culling: angular distance terms · case 05

The visible cap is misplaced when the view centre is off the equator.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Input [lon, lat, lon0, lat0] degrees; sphere R = 6371000 viewed from infinity above (lon0, lat0). cos c = sin(p0)sin(p) + cos(p0)cos(p)cos(dl); points with cos c < 0 are on the far side and return None. Otherwise x = R cos(p) sin(dl), y = R (cos(p0) sin(p) - sin(p0) cos(p) cos(dl)), rounded to 2 decimals.

Why this case matters

Globe widgets and inset locator maps draw only the visible hemisphere; wrong culling shows features through the planet.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression #24	`[-847484.57, -6314201.41]`	`null`	Failed

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