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View Full Version : Voodoo Camera Tracker Help?!?


BlueMouse
03-22-2005, 06:42 AM
Hello all,

I don't know how many of you are familiar with the free match moving program called Voodoo Camera Tracker- But for those of you who are I could really use some help.

I don't know the first thing about matchmoving (that's why I'm trying to learn) so I've downloaded a copy of Voodoo and am trying to match some simple objects into some footage that I've taken with my consumer grade Canon ZR60 Mini-DV cam.

So far, I haven't been able to figure out how to accurately export my tracked scene into Maya.

I don't know how to determine what camera back (back focus?), or focal length settings to use in the tracking software.

When I import my tracked scene into Maya the tracked points don't match up to the footage on my image plane.

Basically I have no idea what I'm doing and need someone who's done this before to point me in the right direction. I've found a couple of explainations and examples on the web but they assume that I have some knowledge that I apparently lack :P

Can anyone with camera tracking experience take pity on me and give me a hand? I'll be forever grateful.

Thanks!

vrljc
03-22-2005, 05:42 PM
I have never touched Voodoo, but I can help you with determining your focal length setting. Basically Maya (and most likely Voodoo as well) requires you to supply a 35mm film camera equivelent focal length because that is the standard that most 3D apps use. However, your mini dv cam's focal length settings are different from a 35mm film camera; so what you have to do is convert the dv cam's focal length settings to MATCH the 35mm film camera's focal length setting.

According to Canon's brochure (off of canon's web-site) on the ZR60, its focal length range is from 2.8-50.4mm. But unfortunately it does not give its 35mm film camera equivelancy, which is exactly what we need to make the conversion.

Can you look at your manual book that came with the camera and find the section on the lens' focal length and see if it includes a 35mm film camera equivelancy?

The reason why the focal length is so important is that if it is wrong when you do the match, your match will come out incorrect.

-jon

BlueMouse
03-22-2005, 09:11 PM
Hey! Thanks for helping me out.

Here's what Canon had to say about the ZR60:

"The lens on the ZR60 will be 2.8-50.4mm. The 35mm equivalent is 7.2x that amount. This will equal 20.6-362.8mm. The image sensor of the ZR60 is 1/6". Effective pixels: tape: approx. 340,000 pixels, card: approx. 447,000 pixels."

I'm still perplexed as to what exactly to do with this information. Hopefully this is where you come in ;)

Thanks again!

vrljc
03-22-2005, 09:48 PM
Great, that is exactly what we want. Well now that you have the conversion factor, you now take the focal length that you used when you shot the video, and multiple it by 7.2 and you now have the focal length value that you will plug into maya and voodoo.

Understand?

-jon

BlueMouse
03-23-2005, 06:03 AM
Hmm. It seems to make sense, but for some reason the Maya camera still isn't matching up to the footage.

The manual that comes with Voodoo also makes mention of "camera back" (back focus?). I don't know if there's any way for me to determine what this is for my camera. This could have something to do with my camera inconsistencies.

I've also read that the size of the CCD and the actual area of the CCD that is used often differ, and that can have an effect on tracking as well.

I've never had any instruction in matchmoving so I'm not even sure how accurate any of this information is. Do you know of any tutorials or step-by-step instructions that are available on the net or from a book? I need all the help that I can get :)

Thanks again for your help!

vrljc
03-23-2005, 10:58 AM
Maya Live uses camera back as a term as well. For these settings it asks you about the size of your film back and regards to film aperature, device aspect ratio, and pixel aspect ratio. Matchmover Pro asks for these same inputs as well, thought they are just named differently.

Basically what it wants to know is what is the size of your cameras ccd and the video's resoultion size to apsect ratios. For example, if you are shooting 640x480 video, then your film aperature will be 1.333 wide and 1 tall. Its device aspect ratio will be 1.333. Its pixel aspect ratio will probably be around 1 unless you imported the footage a bit different. Does voodoo have similar inputs? If voodoo even asks for actual dimensions of the sensor in inches or mm's, look @ ur zr60 manual again and see if it gives you those exact measurements. Then there are your imputs.

I've also read that the size of the CCD and the actual area of the CCD that is used often differ

Are you talking about how most consumer video and still digital cameras do not have full sensors, therefore their focal lengths differ from a standard 35mm film camera? For example, my digital rebels sensor is not full sensored. The lens says I am shooting an 18-55mm lens, but really I am shooting a 28.8-88mm lens, because the sensor is 1.6x smaller than a 35mm film camera. This is where that converting came in earlier. It also has nothing to do with the match, as long as you converted it correctly.

Did you remember to record the focal length setting you used during the shoot?

And here is some documentation that I found:

http://www.digilab.uni-hannover.de/docs/manual.html

-jon

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