Animating camera with parallel / isometric views

Hi! (I suppose this is one for Luc Adriaenssen)

I’m trying to set up a fly-around animation, on a circle-shaped path centered around a set of objects. The end effect is a turntable, but I don’t want to animate the objects to turn around a common Z-axis ,like in this tutorial
https://vimeo.com/118772247

Reason being, that I have a lot of objects which themselves are doing lots of animations, and I don’t want to start messing that up. Rather keep my camera animation separated.

Now, this tutorial shows how to assign a camera to a path
https://www.youtube.com/watch?v=io93m_riFQA

But with parallel perspective (or isometric view), things seem to be a bit trickier.

For instance: I draw the circle, let’s say on the ground level (projected), starting with the center from the camera’s target point (which is at the center of my objects, let’s say its on the 0,0,0) and make the radius to intersect with the camera point. Now I have the circle on the ground plane, but I want to move it up, so the camera point will sit on this circle and so I can use it as a path. but when I do this, the camera point starts moving as well, as if the camera wants to keep the circle within its view.
What exactly is going on here?

Rhino’s views (as well as pictures) are a 2 dimensional representation of a 3 dimensional space. The image is crated by making a mathematical projection - Projection (mathematics) - Wikipedia
This is either a central projection or a parallel projection.
In a central projection the size of objects varies according to their distance to the central point – there is perspective. Because the human eye has a lens it functions like a central projection making people are looking perspective. The centre of projection is what Rhino (and Bongo) calls the “camera location”.
image

In a parallel projection the projecting lines are parallel. Hence the point of projection is as it ware at infinity.
image
Never the less Rhino (and therefore also Bongo) still uses seem like “camera” locations X, Y and Z. This point is are however merely used to define the orientation of the projecting lines, in combination with the targe location. Editing these so-called camera locations gives the most surprising results.

I guess that’s why Bongo’s developers have decided to disable the View Constraints on parallel view. View constraints (like Camera to path) can indeed be initiated but remain greyed-out as long as the view is parallel. Their operation is disabled.
image

It is however possible to use plain keyframed data to animate parallel views
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In this sample model (Arman.3dm (64.3 KB)) I initiated a keyframe at tick 50 by manually rotate the parallel view in animation mode over somewhat about 180°. Then I edited the “Location X” and “Location Y” data in the keyframes making the ones at tick 50 the inverse of those at tick 0. Hence making the turn exactly 180°. Finally I copied keyframe 0 to tick 100 in order to make the turntable-action full circle. The default “Spherical Tweening” does the rest.

Hopefully this technique allows you to elaborate your idea?!?
Luc

PS The image obtained for a parallel view by using the camera command is in my opinion confusing. It still looks very much like a central projection.
image

Good observation. Any suggestion for a better image?
In any case perhaps should be brought to the attention of Bongo developers?

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Indeed, I was planning to create a Youtrack issue, but I didn’t had the time yet to figure out a better way to visualise the parallel projection.
Luc

It’s not that hard. Instead of a pyramid we need a rectangular tube. All the handle points can remain.
image