[ptx] Hugin architectural projection tutorial

[Glenn Barry]

I'm on the list just keep pace with changes to Hugin and I'm not using 
it at the moment so I can't give any specific advice regarding the program.

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.

Horizontal lines are only actually horizontal if they are shot exactly 
perpendicular, otherwise they go either up or down slightly depending on 
where the vanishing points are.

If you don't have good values for this lens from other panoramas, see if 
you can locate good starting values point A, B and C lens coefficients, 
PTLens may help here.

Set one vertical control point set somewhere to the right of the doorway 
where the exterior of the alcove goes from lit to shadow. Use just this 
pair of vertical control points to correct the roll, if any. Make sur 
you place these points as far away as possible to minimise any error.

Then choose rectilinear as the output type, optimise using the known 
good A, B and C co-efficients and things should improve.

Glenn



Stroller wrote:
> Hi there,
> 
> I'm trying to follow the tutorial at http://hugin.sourceforge.net/ 
> tutorials/architectural/en.shtml to remove perspective / wide-angle  
> lens effects on a building and I'm not having much luck. One would  
> think that working on only one image would be easier than working on  
> many, so I don't know how I'm going to get along when I start  stitching 
> panos with Hugin!  ;)
> 
> The original image (resized & converted to jpeg - I've been working  
> with a 45meg tiff) is at http://photography.stroller.uk.eu.org/ 
> Problems/Hugin/Original.jpg
> 
> I loaded this single image into Hugin & in the "Camera & Lens" tab I  
> left "Lens Type" at the default of "Normal (rectilinear)". In Design  
> parameters I set the focal length to 17mm, as I was using my Canon EF- S 
> 17-85mm lens at its widest angle. This set "degrees of view (v)" to  be 
> 93 but I subsequently noticed the "crop factor" box and (in one of  my 
> later attempts) I set this to 1.6 (this suits my APS-C format  digital 
> SLR, I think?) giving a "degrees of view (v)" of 67.
> 
> I initially tried setting control points for two vertical lines down  
> the sides of the church tower and when this gave unsatisfactory  results 
> (see <http://photography.stroller.uk.eu.org/Problems/Hugin/ Hugged.jpg>) 
> I then added control points for a third vertical down  the right-hand 
> side of the building, as in the screenshot at <http:// 
> photography.stroller.uk.eu.org/Problems/Hugin/Screenshot.png>; the  
> results of this were even worse!! <http:// 
> photography.stroller.uk.eu.org/Problems/Hugin/Hugged2.jpg>
> 
> The tutorial does not mention any need to use control points for a  
> horizontal line, but for my last attempt I tried this along the line  of 
> the roof. Once the resulting image has been rotated is somewhat  better, 
> but I'm still not entirely happy with it, and I'm inclined to  think 
> that I've been doing something wrong throughout the earlier  images. The 
> top of the image is more curved than I expected, but I  supposed this is 
> normal, and that I _should_ have expected it; the  door shows distortion 
> from the manipulation, yet the tower itself  really does not seem to 
> have had the perspective improved so much.  
> <http://photography.stroller.uk.eu.org/Problems/Hugin/Hugged3.jpg>
> 
> At each stage I have clicked the "Optimise Now!" button, but have  left 
> everything at their default settings, as I had no idea what to  adjust. 
> Optimisation is therefor of "Positions (incremental, starting  from 
> anchor)" and "yaw" is not ticked (as in the tutorial).
> 
> I would be very grateful for any advice on how to improve these  results 
> and apologise to the list for my poor understanding,
> 
> Stroller.
>  
>