[ptx] Calculated HFOF and Focal Length

[Mike Runge]

Hi,

I took some screenshots comparing focal length calculation between ptgui
(what seems to work correctly) and hugin. I'm having a Fuji S602Z and
normally I use 3 different focal lengths for panos (not in the same pano
;-)):

9.7mm    (43.5mm,   HFOV=32.95, camera default)
7.8mm    (35mm,     HFOV=40.39, max. wide angle)
~6.162mm (~27.88mm, HFOV=49.93, max. wide angle plus converter with factor
0.79)

It looks for me like hugin calculates HFOV directly from exif data well, but
the corresponding 35mm eq. focal length is not correct. That can cause wrong
values for HFOV if you try to insert the 35mm eq. by your own?!

Please have a look at the attached screenshots (I hope you will find the
attached screenshots helpful and not disturbing the list).

PS:
I was some days off and it's quite amazing what has happend meanwhile
(Preview performance for large sets of pictures is: wowwwwwwwww :)))))).

best, mike  


On 11/17/2003, "Pablo d'Angelo" <pablo at mathematik.uni-ulm.de> wrote:

>Hi,
>
>> > >Hmm, what do you call 'correct'?
>> > >
>> > The correct focal length is determined by a factor that differs from
>> > camera to camera. As I understood hugin reads the (real) focal length
>> > from the EXIF data, converts it to a focal length for a 35 mm film and
>> > calculates the degrees of view. Is this right?
>>
>> Yes, and this conversion is based on the size of the CCD chip as
>> compared to the standard 35mm film.
>> Next, the HFOV can be computed from focal length and chip size.
>
>Actually I'm computing the HFOV directly from the EXIF data, without the
additional
>confusing step to the 35 mm equivalent focal length, which can be defined
in
>several ways.
>
>> This is most probably done assuming an error-free optics.  Real optics
are
>> not error-free, and, e.g., cussion- or barrel distortion lead to a
>> slightly larger/smaller FOV when compared to the 'ideal' one.
>
>jep, simple pinhole camera model.
>
>> Therefore I prefer to compute the actual FOV from fitting a 360 deg
>> pano, as this is the important value for stitching.
>> Ideally you do this for all lenses / focal length settings and store
>> them in a library (together with the distortion parameters, of course).
>
>A lens database would be nice to have.. but.. no time...
>
>ciao
>  Pablo
>--
>http://wurm.wohnheim.uni-ulm.de/~redman/
>Please use PGP
>
>

-- 
_________________________________________________________              
Mike Runge
Volksgartenstr. 21 
40227 Duesseldorf
	http://www.trozzreaxxion.net
_________________________________________________________
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