Add ability to fly to a tracked entity

[hpinkos]

Requested in the forum https://groups.google.com/forum/?hl=en#!topic/cesium-dev/a8bwwV3BYuE

Currently, when viewer.trackedEntity is set, it zooms directly to the tracked entity. I would be nice to have a duration option for this behavior to enable flyto functionality.
This function needs to respect the entity.viewFrom property.

[mramato]

FYI, this has been on the entity roadmap a long time. It's a pretty hard problem to solve for moving entities. The best way to do it would be to allow camera flights to be scheduled to occur in scene time rather than wall time, then you can fly to the position you know the entity will be at when the flight is over.

[eric79]

Alternately, you could query for the position of the trackedEntity at each frame of the interpolation to update the goal position. As a result, the camera would follow a curved path to the tracked entity, rather than a straight line to the goal, but the curved path might end up being more visually pleasing (maybe?).

It would also have the side effect that the camera would speed up as it moved since the distance to interpolate to would grow over time. But that might work out well because ideally, you want the camera's speed to match the speed of the tracked object at the time that it arrives at the viewFrom location ... that way you would not only eliminate the discontinuity in position (as we have now when the camera pops from its out-of-date flyTo location to the trackedEntity positoin), but you could eliminate the discontinuity with velocity, too.

Thanks for considering this. It would be a great help to us. And thanks for all the work you do on cesium in general.

[colek42]

Take a look at the paper Physicomimetic Motion Control of Physically Constrained Agents. Might give some insight on how to solve the issue.

[hpinkos]

A few other users in https://groups.google.com/forum/?hl=en#!topic/cesium-dev/a8bwwV3BYuE have recently mentioned they would like to see this as well

[hpinkos]

Also reported here: https://groups.google.com/d/msg/cesium-dev/rOaa0L8_SAg/bk2ApUU_DQAJ

[vekien]

Would like to see this, is it possible as a temp solution to add duration to Camera Zoom, you can set viewer.trackedEntity = entity; and then I can do viewer.camera.zoomOut(100000); however this Snaps to the zoomed out position. If there was a duration and easing it would be super perfect and solve this issue. (If that isn't the hard bit).

[Maarondesigns]

Is there a relatively easy way to simply not move the camera at all when setting trackedEntity? I am trying to set the viewFrom property on the entity just before setting it to be tracked, however I always seem to end up a million miles away