Support "switching between 2D and 3D" use-case

[elemoine]

The "switching between 2D and 3D" use-case is the following: an application with a 2D/3D switch button that changes the view from 2D to 3D and vice-versa (toggle).

The olcs.OLCesium synchronizer proposed in #16 covers that use-case. But the problem is that the ol map is constantly re-rendered when in 3D and when the user interacts with the Cesium globe.

Really, for that use-case we do not need a synchronizer object. What we need is functions helping the application developer to convert ol view states to/from Cesium camera states. These functions will be called when the 2D/3D toggle button is pressed.

Also, we want to show a smooth transition when switching from 2D to/from 3D. And for this smooth transition what we want is to change both the position and the tilt of the camera. This is as described in https://gist.github.com/tonio/750dbc843ef95601c4be (which is referenced in #2).

We'd like that the library provide functions that allow implementing that use-case without having to use lots of math in the application code.

We plan to work on an example implementing that use-case, and, along the way, implement useful functions in the library to support that use-case.

[klokan]

You were faster then me on posting the ticket probably ;-)

Duplicate to #19 in reference to PR #16 for performance improvement.
For animated switching there is #2.

Merged demo of switching between 2D and 3D is at:
http://klokantech.github.io/ol3-cesium/index.html

in the code at examples/main.html

Reopen please, if there is more to be done on this ticket then it is described in #2 and #19.

[elemoine]

This issue was also about us creating an example that implements that use-case, so I'd like to leave it open.

[klokan]

OK. I am sorry then.
Please let's comment on #19 on the performance improvement suggestions.