3D position matching an image

3D position matching an image

by Ryan Hill

on Mar 28, 2012 at 4:22:06 pm

I've been provided an image and I'm supposed to add an effect along a flat surface in that image. The effect uses Trapcode Form and I'm trying to position the camera in 3D space so it looks like the effect is on the surface.

When this kind of thing come up, I always just sort of eyeball it until I get it right, but that's frustrating and I wonder if anyone has a more systematic way of approaching this.

I've searched for tutorials on this, but I mostly just get stuff like this:
http://www.rethinkfx.com/tutorials/compositing3d
Which just off-handedly mentions this as one step among many, but doesn't explain anything about how they do it.

The only measurement they provided me with is the lens length in mm, and even that I'm not sure what to do with because the AE camera is in pixels instead of mm.

Re: 3D position matching an image

by Lionel Kobi

on Apr 2, 2012 at 6:20:07 am

You can change the camera units in After Effects, just double click on your comp's camera and change the units to mm on the bottom left.

I would use the 3d camera projection technique to match your camera, although this is still "eyeballing" to some degree. An excellent tutorial on this can be found on VCP (http://www.videocopilot.net/tutorials/3d_camera_projection/)

Re: 3D position matching an image

by Ryan Hill

on Apr 3, 2012 at 10:39:35 pm

But the tutorial is about distorting the image to do a movement. I don't want to distort the photo at all. I want to add a new element to it. But the new element is supposed to be applied to a very long surface that's viewed from a pretty severe angle, so getting the position just a little bit off makes it really obvious that it's wrong. But it's not obvious how to fix it so I've spent hours just twiddling the position and never quite getting it.

And it seems to me this should be a common problem, but I haven't been able to find any good tutorials that ever get into more depth than, "adjust it until it looks right."

Re: 3D position matching an image

by Lionel Kobi

on Apr 5, 2012 at 1:24:52 am

I'd use the first part of the tutorial to match simple 3d geometry to your image. You don't have to animate the camera or distort the image if you don't need to.

Once you have 3d geometry matched from your camera's perspective, it should be easier and more accurate to place objects in your scene. Having the correct focal length here should help, especially on extremely wide lenses.

The reason I think there is no one click solution for this is that a 3d match moving program requires some motion in order to solve a camera using optical flow. An image simply doesn't provide this information.