11 replies to this topic

[jim c]

I've got a scene part of which I'd like to render in Vue, and part in Houdini. My problem is getting the cameras to match. If I take something simple, like a ground plane, and a cube, I can get the camera in Vue to match the position/orientation of the camera in Houdini. But..
It still doesn't look right. The two images are slightly off, like the perspective is a little different between the two. Has anyone run into a problem like this? What other things do I need to match? As far as I can tell I've got the correct position, orientation, and focal length.

[hopbin9]

I too would like to know how to do this.

[jim c]

Anyone?! Because at the moment I can't see how you'd match stuff, even for still frames, between the two apps.

[3dbeing]

jim c, on 12 January 2012 - 07:29 PM, said:

Anyone?! Because at the moment I can't see how you'd match stuff, even for still frames, between the two apps.

Could it be a units thing? like going from cm -> m or soemthing?

[jim c]

AFAIK no. I'm using the defaults in Houdini, so it's in 1 meter units. I've doubled checked in Vue, and it's also in 1 meter units. The camera settings I'm not so sure about, but I'm also not sure what to look for other than compare focal lengths - which *appear* to be the same.
The pos and orientation seem to be OK. The problem is somewhere in the camera settings I think.

[3dbeing]

jim c, on 12 January 2012 - 07:42 PM, said:

The pos and orientation seem to be OK.

hmmm, how are you doing this by eye in the viewport?

[vectorblur]

jim c, on 09 January 2012 - 11:50 AM, said:

As far as I can tell I've got the correct position, orientation, and focal length.

Are you missing out on matching the Aperture width ? Its the dimension of image sensor, area of exposed film if you are working with physical cameras.

I don't know what its called in vue but often termed as film gate, film back etc.

[Andz]

Sorry I can't help you guys with this, but I'm keeping an eye on this thread as I might be doing some ecosystems animations in the near future and am wondering how good is Vue compared to Terragen and/or full blown 3d package like Houdini for theses type of imagery.

[Chris3D]

Vue is a great package and I have had very good results between Vue and Maya and Vue and 3dsmax.  But for Houdini and Vue - totally different story.  I had this discussion at Siggraph with the folks from Vue last year and they really were not very helpful.  The market they truely support is Vue/Maya and Vue/3dsmax.  So what I finally did is export my scene from Vue to 3dsmax imported there and then exported a FBX file for use in Houdini.

One of the issues I stressed to the folks from Vue since Vue is a procedurally driven package some sort of reader/writer system for Houdini should be fairly straight forward.
This would be a great project and I wish I had time to work it.

Hope this helps....

[jim c]

vectorblur, on 12 January 2012 - 08:59 PM, said:

Are you missing out on matching the Aperture width ? Its the dimension of image sensor, area of exposed film if you are working with physical cameras.

I don't know what its called in vue but often termed as film gate, film back etc.

Possibly - I thought I had tried to look for stuff to match, but it's possible I missed this or misunderstood what I needed to map from Vue to Houdini or vice-versa.

[jim c]

Chris3D, on 13 January 2012 - 07:44 AM, said:

Hope this helps....

Chris, thanks, I'll give that a try. Though I'd really like to know how to do this by hand if it's possible - maybe by seeing what's exported to Max, there's a way to match that in Houdini? And from that work out some formula?

[jim c]

OK I think I've solved this:

Vue has a set of FOV angles one for both vertical and horizontal.  Houdini uses an aperture width, which I assumed, given the way it's laid out in the documentation diagram, to be horizontal. So with the help of a little trig (oh my rusty, rusty brain, I resorted to a web page to look this stupid stuff up, I'm such a little girl), we can take the following from Vue and convert to houdini.

tan( Vue Camera Horz FOV Angle / 2.0) * Vue Cam Focal Length = Houdini Aperture Width / 2

So the default cam in Vue:
tan( 54.4/2.0) * 35mm = 17.9875

Double this, and you get 35.975, that's you're Houdini Aperture value. Match the focal lengths (i.e. set to 35 mm). Match the output size and you're good to go. Don't forget to match aspect ratio.

Now the objects:

Default settings in Vue use Z for up, so to go from Vue to Houdini
z = Y
X = X
y = -Z

Rotation is slightly more fun
From Vue to H
Take a null , rotate it 90 on X
Parent the light (or whatever) to the null.
Vue Pitch = rx + 180
Vue Roll = ry
Vue Yaw = rz

I made a sample scene of a default cube in vue (6 X 6 X 6), default cam and light settings. Duped in Houdini.
After rendering both images and then comping them to check, it looked really damn close. Everything including shadows seemed to lined up. Can anyone tell me if this makes any sense or if I've made some completely idiotic assumption?

Edited by jim c, 19 May 2012 - 01:55 PM.