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trueSpace camera and real camera correspondance // The Garage

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Post by Emmanuel // Apr 27, 2008, 7:00am

Emmanuel
Total Posts: 439
pic
When blending 3D scenes with real world pictures, I always fight with real lenses and virtual camera correspondances.
I wondered if I could get a rule that would allow for a plugin development : a way to put in my scenes a virtual camera with a length in millimeters rather than the default Z value in meters that correspond to nothing.

So today, I placed my camera on a tripod, drawn marks on the floor every meter, and took pictures at various zoom length ; next, I reproduced that scene in trueSpace, loaded the photos one by one as background picture and tried to change the Z value to make the real and virtual marks to match.

I tried 2 different zooms to balance the possible changes due to lenses nature and possible deformation.

Here is the result :

Zoom Canon 17-40 mm :

Z=0.5
17 mm

Z=0.58
21 mm

Z=0.69
24 mm

Z=0.79
29 mm

Z=1.015
35 mm

Z=1.13
40 mm


Zoom Canon 28-135 mm :

Z=0.83
28 mm

Z=1.029
35 mm

Z=1.417
50 mm

Z=1.9
70 mm

Z=2.85
100 mm

Z=4.19
135 mm


As you can see, there is no ratio, no rule, between these values.
Perhaps because the ground I drawn the marks on was not all horizontal ; also the lens deformation may change the picture geometry at some angles.

However, we can notice that we can approach the right angle by dividing the length in millimeters by 34.
The formula could be :

Zoom length in millimeters (stored in the photo's METADATA information) / 34 = camera Z value in meters.


So I will not come with a plugin this time :o ; only with a trick that may help to get an easier camera setup for photo/3D integrations.

Post by frank // Apr 27, 2008, 10:06am

frank
Total Posts: 709
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This is really interesting.


Back when I was working on the VD2TS (http://www.frankladner.com/vd2ts/) application, the scale value conversion was one thing I didn't figure out.


When converting camera-matched footage from voodoo to trueSpace, I just go in and delete all the scale values for the camera, then change the scale of the first keyframe based on the background (reference) footage, and go with that.


I may revisit VD2TS and see if I can get this formula to work.


Thanks!


P.S. This may or may not be of interest. This is what I came up with when trying to figure out what values to plug into Voodoo for my specific camera. This may help other Voodoo users with different cameras (originally posted on digilab/Voodoo forums in '05):


CANON GL2


Film Back: 3.6mm x 2.7mm

Focal Length: 4.2mm (at full wide)



I believe Film Back is the actual image plane. In a 35mm film camera, this would be 36x24, for instance. I did some searching for 1/4" CCD sizes (GL2 has this) and I found that it should be 3.6mm x 2.7mm.

Post by hultek43 // Apr 27, 2008, 10:24am

hultek43
Total Posts: 234
 Here's a similar thread from way back when regarding FOV. http://forums.caligari.com/discus/messages/1580/9548.html?
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