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Shifting Nested Camera Issue

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Steve Bentley
Shifting Nested Camera Issue
on Jun 5, 2018 at 6:21:43 am

Have a look at this file. Its an AE 2018 15.01.

I have two cameras as children of a null. They are both identical, both in where they visually look like they are pointing and in their values. (one is a duplicate of the other)
If you go to the front view so you can see their wire cages, select one of the cameras and then unparent it from the null. The one you unparent will rotate ever so slightly along its axis.
It doesn't matter which one you choose, either will do this. There is no animation on these elements.

This came about because I was getting errors in camera position and orientation when exporting for C4D. If you bring just a camera in, all is well. But bring a camera that is being dragged about by a null, and C4d creates slight differences, especially if the AE camera has been rotated inside the null.

I think this has to do with the POI fighting with the rotation values in AE. I'm not sure what the advantage is with a POI that you can rotate away from - so the rotation values aren't relative to the cameras world space but to the POI. And the POI values become local values (as one would expect) if the camera becomes a child of another object or null. But it seems the rotation values do not. Notice when you unparent the camera how the rotation values don't change even though the null's own rotation should add to the child's rotation numerical values once it is unparented. I think this is because those camera rotation values are in camera space relative to the POI.

Because C4D doesn't work this way (you can have a target OR you can rotate the camera but you can't do both) I thought I could tweak the values in C4D to make the cameras match. I tried using a target in C4D to simulate the POI and the rotation offsets from the POI, but the position values of the Target were out by exactly a factor of 10 in the Y.
Even accepting that oddity and just going with it, the rotation values seem to be magnified a little as well in C4d.

I was using the duplicate second camera in AE and uparenting it to get world values that I could transfer manually to C4D. And that's when I noticed the shift.

You can also see from the Jpgs that, even by eye, the cameras have a different angle between aE and c4d even though the values say they are the same.

12429_nestedcameraissue.aep.zip






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Cassius Marques
Re: Shifting Nested Camera Issue
on Jun 5, 2018 at 1:40:26 pm

[Steve Bentley] "Notice when you unparent the camera how the rotation values don't change even though the null's own rotation should add to the child's rotation numerical values once it is unparented."

That's not how AE handles that, you're getting your rotation values being thrown into the orientation properties, the slight change you're seeing is probably some gimbal math going on.

Anyway... how are you bringing into AE the camera info? Cause when I exctract an example here i doesn't come with POI.

Cassius Marques
http://www.zapfilmes.com


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Cassius Marques
Re: Shifting Nested Camera Issue
on Jun 5, 2018 at 1:45:16 pm

Scratch that... You're going AE -> C4d, my bad. Have you tried turning off POI in AE prior to exporting to see if you get the same results?

Cassius Marques
http://www.zapfilmes.com


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Steve Bentley
Re: Shifting Nested Camera Issue
on Jun 5, 2018 at 7:30:54 pm

Thanks for having a look Cassius.
I though it might be a bit of the ol gimbal thing.
I wasn't clear on what you meant by turn off the POI on export. First I didn't know you could do that, and second I'm not sure it matters - the POI doesn't come into C4D (if it did I think it would have to generate a target tag and object). But it could be adding the POI to the global rotation and that's probably where my problem begins.

Oh wait a minute - do you mean use a single node cam instead of a 2 node cam? Ya that might be the ticket!



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