[ptx] Calculated HFOF and Focal Length

[Mike Runge]

Hmm,

maybe I was a little bit short about what which screenshot shows?!

ptgui_exif_43:
ptgui values for focal length 9.7mm

hugin_exif_43:
hugin values directly from Exif data, no keyin.

ptgui_exif_35:
ptgui_values (keyin focal length) and hugin values (keyin focal length) for
7.8mm

ptgui_exif_28:
ptgui_values (keyin focal length) and hugin values (keyin focal length) for
~6.162mm

I hope, that it is now more understandable?! Sorry for the amount of pictures
and the uncomplete describtion :-( 

best, mike 


On 11/18/2003, "Mike Runge" <mike at trozzreaxxion.net> wrote:

>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
>_________________________________________________________
>
>

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