[Rd] navigation mode(s) in rgl

Michael Sumner mdsumner at gmail.com
Thu Nov 5 00:56:33 CET 2015

Hello, I've CCd' Duncan Murdoch as the rgl maintainer, but I'm also keen to
hear from the broader community of any insights.

In rgl my understanding is that there's only one rotation-navigation mode,
where you left-click hold and the view pivots abound the centre of the

In other tools, including Google Earth, that is the default behaviour but
there's also a click-centric mode where the view pivots about the point
clicked on.

I haven't found the right terminology for this, but I call it

1) Data-centric navigation, rotating about the centre of the data in  the
scene (invoked by left-click-drag in rgl and GE and others)
2) Click-centric navigation, rotating about the point clicked on (invoked
by centre-click-drag in GE and others, but not rgl)

My questions:

1) I'd appreciate any guidance on my terminology here, whether I'm making
sense and ask for pointers to resources that explore this properly
2) Is there scope to add this "click-centric" navigation to rgl? I'd
appreciate any pointers to how it could be done - is it an rgl-level
feature, or deeper down?

I know that "click-centric" clicked-on point has a different meaning in
different contexts, in GE clearly it finds the nearest point intersecting
the globe surface since that is a always-present structure, but other tools
must have rules to specify where the pivot point is - either intersecting a
data element or somewhere in the scene.

The data-centric mode is fine for small scenes with a limited scope, but
when the extent covered by data is large it's quite unwieldy to focus in on
specific parts of the scene. I know this could be controlled by
pushing/popping elements in the scene but the navigation mode obviously
offers more flexibility.

Thank you.

Cheers, Mike.

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