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3D tracking mismatch with Houdini (fusion 16)

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matevil
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3D tracking mismatch with Houdini (fusion 16)

#1

Post by matevil » Tue Sep 10, 2019 3:42 am

Hi there,

I'm relative new in this forum and usually I'm working on FX in Houdini and not in Fusion, but now I came back on it for create a fast tracking and after see more video tutorial on this subject I open one discussion here because I got a strange issue. So...

here you can download the fusion files, sequences and FBX
http://www.art2upz.com/test_bridge.zip

I create also one example with I can share with you. Essentially I create a tracking on Fusion, 3D Camera and some reference geometry.
When I import in Houdini (same range and FPS) I tried:

  • to apply the sequence inside the camera like background - mismatch

Image

  • apply the sequence on plane generated by fusion before - works

Image

I render some geometry and when came back on Fusion for composition all is wrong! why???

Image

I attached also some images for help to understand better.

This is the tracking create by Fusion before export in FBX

Image

Thanks and have a nice day
Matteo


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matevil
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Re: 3D tracking mismatch with Houdini (fusion 16)

#2

Post by matevil » Wed Sep 11, 2019 1:51 pm

maybe I found a way for fix it. There are always a few mismatch but I think because the tracking is not 100% correctly, anyway the solution is in the value of camera inside Houdini should be change the aperture like the value of Fusion because this parameter doesn't take correctly when export and import.

Mat


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Midphase
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Re: 3D tracking mismatch with Houdini (fusion 16)

#3

Post by Midphase » Wed Sep 11, 2019 9:59 pm

This is an issue since for some bizarre reason Fusion measures the FilmBack value in inches whereas Houdini does in the proper mm value.


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SirEdric
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Re: 3D tracking mismatch with Houdini (fusion 16)

#4

Post by SirEdric » Sat Sep 14, 2019 11:35 am

Midphase wrote:
Wed Sep 11, 2019 9:59 pm

FilmBack value in inches whereas Houdini does in the proper mm

Not sure if there's a 'proper' way to measure them. Both imperial and metric values are used in different locations of this planet....:-)


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Midphase
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Re: 3D tracking mismatch with Houdini (fusion 16)

#5

Post by Midphase » Sun Sep 15, 2019 11:53 pm

Awww, come on man. Photography has always relied on mm and motion cinema adopted that standard. I have never heard of anyone shooting on Super 1.37795....have you?


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Re: 3D tracking mismatch with Houdini (fusion 16)

#6

Post by SecondMan » Sat Sep 21, 2019 10:25 pm

That's actually not quite true. From what I remember, film sizes/film backs/film formats are more often than not expressed in inches rather than mm, probably depending on when and/or where they originated. 35mm film (135 designation from Kodak) is only one (of a minority) expressed in mm (correct me if I'm wrong). It's widespread, sure, but that doesn't mean it dictates a standard.

That said, it would be nice if Fusion could perhaps have a preference to set film back in either inch or mm...

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Re: 3D tracking mismatch with Houdini (fusion 16)

#7

Post by Kristof » Sun Sep 22, 2019 12:43 am

Well, when dealing with lenses and cameras you better familiarize yourself with all these formats and deal with the math. And when things go wrong, best bet is to set your film back to the "default" of still photographic film, the 35 mm format (36 mm by 24 mm). And fit things on the horizontal axis.

So in that sense, I get Midphase's reaction.

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Re: 3D tracking mismatch with Houdini (fusion 16)

#8

Post by SecondMan » Sun Sep 22, 2019 2:07 am

Sure, sure, I get it too, don't get me wrong - but when was the last time you've had to deal with the 35mm "default"?

Not necessarily to do with a Fusion/Houdini mismatch - here's a not too bad resource for getting camera format settings: https://vfxcamdb.com/

Inches and mm provided - something for everyone 😊

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matevil
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Re: 3D tracking mismatch with Houdini (fusion 16)

#9

Post by matevil » Thu Oct 03, 2019 11:47 am

Thanks to everybody... but I'm confusion now... what the "final" solution ?

Thanks
Matteo

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Re: 3D tracking mismatch with Houdini (fusion 16)

#10

Post by millzo » Thu Oct 03, 2019 10:26 pm

matevil wrote:
Thu Oct 03, 2019 11:47 am
Thanks to everybody... but I'm confusion now... what the "final" solution ?
This thread has definitely turned to confusion so here are some answers.

As others have mentioned there is a difference in aperture/film back units between fusion and houdini. Inch units are not uncommon for aperture paramaters in software. I haven't found an automatic conversion in the fusion export settings so I had to do a manual conversion. The values that are in the houdini camera after import are quite strange. I'm not sure what kind of calculation is done during the export from fusion to achieve those numbers so here is what I did.

  1. Copied the aperture from fusion and converted inches to mm 1.007874 x 25.4 = 25.599999
  2. Pasted the result into the aperture parameter of the houdini camera.
  3. Copied the focal length from fusion and pasted it in the houdini camera focal length parameter.
This method may not work for shots that have animated parameters such as zoom lenses. Exporting cameras from fusion is probably rare at this time, but it is interesting to see what people are doing with the features offered.

Here is a screenshot of the result.
lensConversion.PNG
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