Re: Anyone knows how maya computes filmback translation?

["Tim Leydecker" <BauerOink(at)gmx.de>]

An extra shot in the blue, at least for testing purposes,
make sure you have identical settings for outputresolution
and pixelaspectratio set in both Maya and XSI, otherwise
Maya may give you unexpected results, f.e. when you have
specified 640x480px in the RG but a 16:9 camera format,
you´ll get your cameraoutput "squeezed" into the 4:3 render.

Could be one of the reasons for misalignements, another is
the optical center shift (e.g. "pseudo shift lens"), I´m not sure
wether Maya supports this feature - architectural renderings?

Up until now I helped myself by setting the filmbacksize to the
aspectratio, e.g. a 16:9 format would be 1.778:1 (inch) in Maya
and XSI, 768x432/1024x576/1280x720/1920x1280 (square px)
as (preview)resolutions, I was able to mix renderings with these
settings and a camera exported via *.xsi between Maya and XSI.
I´ll usually leave shifts untouched but use 21-75 (pseudoMM) lenses,
where a 50 (pseudo mm) lens pretty much equals the "normal viewing".

I´ve never tried to match to real footage, thought...

Cheers

tim


----- Original Message ----- 
From: "Brent McPherson" <brentmc(at)Softimage.COM>
To: <XSI(at)Softimage.COM>
Sent: Monday, December 04, 2006 2:56 PM
Subject: RE: Anyone knows how maya computes filmback translation?


> Hi Philipp,
>
> I don't have Maya to compare with but in tech-speak a normalized value
> is a value between 0 and 1. So if you want to produce a normalized value
> > from the XSI settings you would take the horizontal offset and divide by
> the filmback width like this:
>
> -0.0307 / 0.9802 = -0.0313
>
> Now, based on your guesstimate in Maya of -0.065 it looks like there is
> a scale factor of 2 in there so I would expect the equivalent Maya value
> to be:
>
> -0.0313 x 2 = -0.0626
>
> (and to go from Maya to XSI just take the normalized value, divide by
> two
> and finally multiply by the filmback width)
>
> Of course this is just a guess on my part but you should be able to
> verify whether this is the case by running a few different settings
> through both XSI and Maya.
>
> Hope this helps.
> --
> Brent
>
> -----Original Message-----
> From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf
> Of Philipp Oeser
> Sent: Sunday, December 03, 2006 4:22 AM
> To: XSI(at)Softimage.COM
> 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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