From the whole-globe view the camera could end up facing empty space with
only stars on screen. Cesium's free look (Shift+drag) turns the camera in
place, and from 18,000 km the planet's edge is only about 15 degrees from
nadir, so a few drags turned it out of frame. The rolled pose was then
saved into the share hash, so a reload or shared link opened on stars too.
- Allow free look only below 1,000 km. Orbit, tilt and zoom are unchanged.
- Measure how much of the frame shows the planet's surface by casting a
32x18 grid of view rays at the WGS84 ellipsoid. While the scope mask is
on (the default) only the rays inside its keyhole count, since the mask
hides or dims the rest of the frame.
- When a camera move ends above 1,000 km with no ray on the surface, turn
straight down at the same position and heading. Limb glow and a sliver
up to about one grid cell thick can count as out of view. The end of a
move comes from Cesium's moveEnd and from a check of its own that
samples the pose every 250 ms after moveStart and acts once it has held
for half a second: at some of these poses the camera drifts by a
rounding error every frame, so Cesium never sees it stop and never
raises moveEnd. The zoom-out guard from #1522 keeps wheel and pinch
zoom-outs in view; this catches the other ways a move can end looking
away, such as a saved or shared view that did, or a
drag that Cesium turns into an in-place look below its 7,500 km
trackball height (one that starts on the stars, or a tilt drag with the
screen centre off the planet). Views with more surface, tracked or
locked cameras and the 2D and Columbus modes are left alone.
- Voice tilt and in-place turns of a free 3D globe camera above 1,000 km
stop when about a tenth of the frame still shows the planet (or about as
much as it showed when it started, two grid cells of sampling noise
allowed), never below about 1% of the visible frame; a view that already
shows less only keeps or gains what it has. A turn that cannot go half a
degree further without crossing that limit is refused with a reason
instead of reported as done, and a turn it accepts turns at least that
half degree. A turn that keeps or gains surface is not refused, even
after the window has been resized, except that near the limit, where the
planet's edge crosses the sample grid, sampling wobble can occasionally
refuse one (most often above about 15,000 km and on phone or ultrawide
frames); nothing then turns away from the planet. A turn that starts
where the last voice turn left the camera keeps that turn's limit, or a
higher one if the planet now fills more, so repeating the request does
not take any more; once anything else has moved or turned the camera, a
turn is measured from what is on screen. A request made while the camera
is tracked is judged by the pose voice's release of the follow camera
will leave, before that release, so a refused turn keeps the tracking.
The frame measure and the look-step limit live in src/globeInView.js,
shared by the viewer and the voice camera verbs.
Manjunath
99520b529c