Re: Anyone knows how maya computes filmback translation?

[Philipp Oeser <philipp.oeser(at)liga01.de>]

Thanx Tim,
FocalLength <> AngleOfView conversion is not the problem (at least thats 
what I think, a little unsure though)
since I'm just taking XSI's FocalLength and pass it over to Maya 
(together with  the apperture). Fom that (FocalLength + AppertureX 
+AppertureY)
Maya automatically computes the right AngleOfView.

Correct me if I'm wrong
XSI: FocalLength in mm
XSI: apertureX in inches
XSI: apertureY in inches

MAYA: FocalLength in mm
MAYA: apertureX in inches
MAYA: apertureY in inches

So I can paste those 1:1 from XSI to Maya, right? AngleOfView is just 
dependent on those three?

Now the problem arises with OpticalCenterShift aka  FilmbackTranslate

XSI: OpticalCenterShiftX in inches (-0,0307 in my example)
MAYA: FilmTranslateH ??? (normalized??) ??? (~ -0.065 in my example for 
a good match)

So sorry, still dont get it...
Philipp


Tim Leydecker schrieb:
> Hi Philipp,
>
> I guess you allready tried the easy way of exporting the
> camera via .xsi and *.fbx (at least for getting an idea of
> the required conversion settings or offsets).
>
> IÂm not sure if this helps but Andy Walker has posted
> two snippets of valuable info over at the maya(at)highend3d.com
> list, here it is pasted in (RE: Converting AngleofView to Focal Length):
>
> -------------------
> Yeah, Maya cameras use horizontal angle of views, so using all the
> horizontal data, the formula is:
> horizontal angle of view = 2 * atand(0.5*film_back_width/focalLength)
>
> The film back width needs to be converted from inches to mm,  so
> multiply it by 25.4.
>
> e.g. on a 35mm maya camera with an aperture of 1.417 inches:
>
> float $angleOfView = 2 * atand(0.5*((1.417*25.4)/35));
> print $angleOfView;
> // 54.421607
> ------------------------
>
> Whoops, i see you want the other way around..
> well that should be:
>
> float $angleOfView = 54.421607;
> float $horizontalAperture = 1.417*25.4;
> float $focalLength = (0.5*$horizontalAperture)/tand($angleOfView/2);
> print $focalLength;
> // 35mm
>
> ------------------------
> According to Soren Kurgan Jacobson (same thread):
>
> > search the maya mel scripts, if I remember correctly the whole calc 
> > is in there
>
> ----------------
>
>
> Hope this helps,
>
>
> Cheers
>
> tim
>
>
>
> ----- Original Message ----- From: "Philipp Oeser" 
> <philipp.oeser(at)liga01.de>
> To: <XSI(at)Softimage.COM>
> Sent: Sunday, December 03, 2006 5:22 AM
> Subject: Anyone knows how maya computes filmback translation?
>
>
> > Hi everyone,
> > I need to convert a XSI camera to Maya and I just cant figure out how 
> > maya computes the translation on the filmback. (their docs say "The 
> > values are normalized with respect to viewing area").
> > An example:
> > I have a 0,9802 inch x 0,7352 inch filmback in XSI with an -0,0307 
> > inch horizontal filmback translation/optical center shift (here it is 
> > all in inches)
> > The cam in Maya (same filmback of 0,9802 inch x 0,7352 inch) seems to 
> > match at a Filmback translate H with a value of about -0.065. (All 
> > other settings in Filmback are standard, no scaling, no filmoffset, 
> > no lenssqueeze) (and matching also seems to be dependent on overscan).
> > Sorry, it's late at night and I cant get it right...
> >
> > Any ideas?
> > Thanx in advance
> > Philipp
> >
> > --
> >
> > Philipp Oeser
> > Liga_01 Computerfilm GmbH
> > www.liga01.de
> >
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--

Philipp Oeser
Liga_01 Computerfilm GmbH
www.liga01.de


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