Rotation point for parent track motion

[Mike Kujbida]

I’m pretty sure this is what you want (thanks to John Rofrano for the tutorial).
3D Track Motion: Changing the Pivot Point

[Tom Keane]

Thanks for the reply, Mike.

John has some great tutorials, but in the tutorial you reference, he is moving the pivot for a single plane. In my case, there are 2 intersecting planes to rotate so the pivot point is somewhere offset in both the x and z directions (I think). I just don’t know where or how to compute it or how to set it. Can’t understand why I’m having so much difficulty figuring this out. At this point, I’ve about given up on using the effect, although I know it can be done.

Thanks for trying.

[Tyson Onaga]

Sounds like you are trying to move two images in 3D, like 2 faces of a cube. If so, Theo van Laar posted a sample here:

https://forums.creativecow.net/readpost/24/931482

It has a cube rotating through 3D space. Might be worth a look.

[John Rofrano]

[Tom Keane] ” In my case, there are 2 intersecting planes to rotate so the pivot point is somewhere offset in both the x and z directions (I think). I just don’t know where or how to compute it or how to set it.”

You don’t want to change the pivot points at all. As soon as you are using more than one track, you need to use 3D Parent Motion to solve the problem. Try this tutorial:

3D Parent Motion: Moving Planes

In the tutorial the planes are parallel and in your case they are perpendicular but the method is the same. Use 3D Track Motion to position the tracks and then use 3D Parent Motion from a third track to control the movement of the other two.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Tom Keane]

John, I’m a fan of your tutorials and had studied that particular one. However, in my situation, my 2 photos don’t fill the 720×480 frames horizontially, just vertically, so when I match up the photo edges at 90 degrees, I’m actually causing the underlying full frames to intersect (bisect?) which seems to throw off the center of rotation. When I use the parent motion, the photos rotate, but in a wide arc (probably because it’s the underlying full frames that hold the photos that are actually being rotated). The pivot seems to need to be shifted, but I don’t know how to get it accurate.

Thanks for the response.

[Tom Keane]

Ok, OK, I figured it out…. actually it was john’s emphatic statement that got my head clear. He said “You don’t want to change the pivot points at all.”

I restarted and found that by moving the 2 photos back and forth against each other using their individual track motion positions (while watching the parent motion in the preview), I was able to see the width of the photos in the position box. Then using John’s point of not messing with the pivot, I positioned the front photo forward on the z axis by half the width of the left side photo. Then I moved the left side photo along the x axis by half the width of the front photo. This seemed to position the photos the correct distances from the center point (the pivot). Now when I used the parent motion to rotate, they move as I want (at least close enough), and I didn’t mess with moving the pivot.

Can’t believe I spent so much time on this and all it took was a simple whack in the head from John to see the light. Thanks loads.