[ptx] Hugin architectural projection tutorial

[Rik Littlefield]

Stroller,

Looking at your 
http://photography.stroller.uk.eu.org/Examples/Hugged.jpg , I worry that 
you have let the optimizer adjust too many things without enough 
information.  The fact that you're getting curved lines using 
rectilinear projection and a rectilinear lens suggests that the a/b/c 
distortion parameters have gotten out of control.

I took a quick stab at your image, working from 
http://photography.stroller.uk.eu.org/Problems/Hugin/Original.jpg .  
First I came up with 
http://www.janrik.net/PanoPostings/Stroller20060312/StrollerCorrected.JPG 
.  The tower is straight, the horizontals are straight (though 
converging to the left because of your vantage point), and to my eye, 
the picture has a "believable" feel.  (Of course, I don't know what the 
real building looks like!)

The way I did this, was to set just two vertical controls as shown in 
http://www.janrik.net/PanoPostings/Stroller20060312/StrollerPTS.jpg .  
Then I turned off lens corrections (a=b=c=0) and optimized just pitch 
and roll, leaving yaw=0.  This corresponds to correcting the vertical 
tilt of your camera, but not the horizontal tilt caused by your 
off-center vantage point.

I also tried setting a horizontal control at the roofline, and 
optimizing yaw along with pitch and roll.  That corresponds to 
correcting for the off-center vantage point too, so that the "virtual 
film" would be parallel to the front of the building.  That made the 
building look good (better?), but there wasn't enough sky and tree to 
fill the frame on the right side.  See 
http://www.janrik.net/PanoPostings/Stroller20060312/StrollerPTS2.jpg and 
http://www.janrik.net/PanoPostings/Stroller20060312/StrollerCorrected2.JPG .

I did these tests with PTGui because that's what I normally use.  But 
the corrections should be just the same with Hugin.  Note that these are 
crops from a larger panorama.  The original outputs had a lot of black 
space, see for example 
http://www.janrik.net/PanoPostings/Stroller20060312/StrollerCorrected2a.JPG 
.

Hope this helps,
--Rik

Stroller wrote:

>
> On 12 Mar 2006, at 07:40, Glenn Barry wrote:
>
>>
>> Quick answer, it's from such a low viewpoint don't try and correct  
>> the convergence, it's an artistic choice I know, but from  
>> experience, if you remove the convergence completely, the  impression 
>> of height has gone also.
>
>
> Thank you for your advice.
>
> From an artistic point-of-view I have kinda mixed feelings about  this 
> image. I don't really think it's a "keeper" (although having  stared 
> at it for so many hours today & yesterday it's starting to  grow on 
> me!) but I just thought it'd be suitable for this kind of  
> experimentation.
>
> My initial thoughts on seeing this Hugin tutorial were "why would  
> anyone want to remove the perspective?" as I tend to see such  
> convergence as an intrinsic & artistic aspect of photography, part of  
> what I find interesting about the pursuit. However I was intrigued by  
> the tutorial author's words a "way of presenting architectural  
> photographs"; I have read a very little of Canon's pan-&-tilt lenses  
> and was curious to see the results of this "correction" using Hugin  
> (and the Panorama Tools, of course).
>
> The wide-angle perspective was forced on me by my surroundings -  
> distancing myself from the church to use a longer focal-length caused  
> the trees on either side of the frame to obstruct my view - so this  
> was an interesting experiment for me. I am not so happy with other  
> distortions (bend of the roof) introduced by this "correction" and I  
> don't have immediate plans to frame the result, but I find it  
> interesting that compared to the original the church tower is more  
> "bold" and draws the eye more.
> http://photography.stroller.uk.eu.org/Examples/Hugged.jpg
>
> Stroller.
>
>