View Full Version : struggling with getting a building straight - ongoing issues - please help.
09-27-2011, 03:53 AM
John Houghton gave me a link to a website which shows how to straighten buildings etc in Ptgui using T1 control points. I've done that with the vertical columns in this attached image but as you can see the roof is not level nor is the foreground.
Is there one way of levelling verticals and one for horizontals.
I'll try to contact John but if anyone see's this and can help I'd appreciate.
Incidentally this is approximately a 180 degree pano'
09-27-2011, 06:39 AM
you probably need to use another projection for angle of view of ~180 deg. A panini projection may be a good choice.
09-27-2011, 08:04 AM
Nick is correct. You can only straighten all the straight line features if you use rectilinear projection. However, you then have to accept a field of view considerably less than 180. If the fov is too big, the edges will become stretched. This is a rectilinear version of your image, and you will notice the distortion on the lamps:
09-27-2011, 09:15 AM
... using T1 control points. I've done that with the vertical columns in this attached image ...
I don't think the main columns have vertical sides - the columns look narrower at the top than the bottom. There are lots of other verticals to choose from though.
09-28-2011, 02:17 AM
Thanks very much for your reply and also taking the time to show me your corrected example. I was trying to copy a shot taken by George Meis a postcard photographer from Greece. I can only assume he used a panoramic film camera, actually I think he uses a Fuji GX617.
John I'm pretty new to taking panoramas I'm not interested in taking 360 deg work but I've looked at some of those 'virtual reality tours' you now begin to see on the internet. I'm attaching one here http://www.gigapan.org/gigapans/48492/
This pano' shows Dubai from a roof top, when you look at the buildings in the distance they are all standing vertically.
Am I missing an important point here, can my pano's not be corrected because they are too close up?
I'd really appreciate help here because quite frankly I'm beginning to tire of the NN5 and wasting hours trying to take shots that just end up in the trash.
09-28-2011, 02:35 AM
It is very kind of John to spend time playing your images and offering advice for you. But have you spent some time reading the tutorial about pannini projection? Don't you see the problems in some of the images are very similar to yours?
BTW, Pannini projection is Vedutismo in ptgui.
09-28-2011, 02:43 AM
It doesn't matter what camera or lens you use, the final result will be the same when you shoot a scene from a fixed viewpoint. A panoramic film camera simply delivers an image in cylindrical projection. That can be input to PTGui and rendered in other projections and levelled, etc, the same as for other camera images.
The Dubai panorama suffers from exactly the same problems with horizontal features as yours. Look at the curving rail at the bottom, which is straight in reality. It's probably rendered in either cylindrical or equirectangular projection. For both of these, all vertical features will be vertical when properly levelled, just as they are in yours.
As I have already indicated, you must use rectilinear projection if you want to preserve all verticals and horizontals. That means restricting the fov to around 100 degrees, to avoid stretching at the edges. To accommodate a wide building, you must position the camera sufficiently far away so that the angle of view is no more than 100. If that's not possible, you must either accept a much larger fov due to the closer camera position and put up with curving horizontals in a cylindrical projection, or resort to editing tricks or unusual projections.
For example - you can take shots from different points spread along the front of the building, and join these together in Photoshop. This is tricky because of the perspective differences between shots, but can work ok for reasonably flat subjects. It's a lot of work, though.
09-28-2011, 02:28 PM
Nick, I looked at the link you gave but there was no tutorial just a short paragraph at the bottom, sorry if I sounded ungrateful, I think the tutorial was missing from the link.
John, I understand a great deal more now, the building in my photograph would definitely have had a view of over 100' certainly closer to 180'. I couldn't stand further back so I think as you are saying the only way to make this actually work is to take a shot, move say 5metres to the right and take another with the camera height and angle identical and move along a line until the building is shot.
I can see the curving rail in the Dubai shot but of course the buildings are a large distance apart.
Thanks for your help, I will play a bit more with this but personally I feel there is limited success in this kind of shot.
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