Post Number: 5
|Posted on Friday, July 20, 2007 - 12:48 pm: |
I recently shot another 360 degree two-row-panorama and stitched it using the spherical projection.
I relized an strange distortion in the image and I am not sure if itīs a problem that occurred during the making of the photos or if itīs a problem of the projection.
First, let us have a look at the whole panorama for an overview (sorry for the lack of details, the original is about 17.000 pixels wide...)
I have been standing in the middle between the "Bahnhof" (subway station) and the illuminated office tower with the glass facade within a distance of about 10 meters each.
I had to tilt up my camera for the second row of the panorama to extend the field of view vertically.
when stitching the upper row - using spherical projection - I relized that the skyscraper showed an increasing level of distortion the more you look upwards.
See the detail for explanation: the floors of the tower should be the same height.
The result does not look good if you are willing to print a panorama. The curved roof of the "Bahnhof" is ok for me but i dislike the decrease of the ceiling height in the buildings ;-)
Is this a problem I could avoid using e. g. cylindrical projection?
Before anybody says "Go find out yourself!", please keep in mind that the source images (30 fotos) are 60 MB each and it takes about 2 hours to stitch them. On a dual-core machine. :-)
Any hints welcome.
Post Number: 312
|Posted on Friday, July 20, 2007 - 2:31 pm: |
The "distortion" you see is simply the consequence of using spherical projection. The image is painted onto the inside of a sphere which is then unrolled in a way that's similar to the familiar Mercator map projection commonly used for world maps.
This happens with all full sphere images. Take a look at this full sphere image, for example:
Mellon Square, Pittsburgh, PA (unrolled)
As in your image, the floors get closer together as you go up the buildings. But when you put the same JPG file into a VR viewer, it looks perfect (tilt the view up to see the tops of the buildings):
Mellon Square, Pittsburgh, PA (VR)
You can eliminate spherical distortion by using cylindrical projection. But cylindrical projection has its own idiosyncracies. First, cylindrical projection cannot represent more than about 60 to 70 degrees vertical field of view above and below the horizon (about 120 to 140 degrees total). Second, cylindrical projection has its own type of distortion.
For comparison purposes, I made a particular scene with both spherical and cylindrical projection. It's 360 degrees horizontal by about 65 degrees above the horizon (equivalent to about 130 degrees if it were symmetric above and below the horizon):
Fifth Avenue Place, Pittsburgh, PA (spherical)
Fifth Avenue Place, Pittsburgh, PA (cylindrical)
Each is distorted in its own way. This is an unavoidable consequence of trying to show an extremely large field of view on a flat display. Perhaps you find one of these images more acceptable--it's a personal, esthetic choice.
(Message edited by jstrait on July 20, 2007)
Post Number: 313
|Posted on Friday, July 20, 2007 - 2:33 pm: |
P.S. A future release of The Panorama Factory will contain a command for converting between spherical and cylindrical projection. This will enable you to stitch once using spherical projection and then convert quickly for comparison purposes.
Post Number: 6
|Posted on Friday, July 20, 2007 - 2:54 pm: |
Thank you for the quick answer.
I will experiment a little with the different projection types to find the one that gives the most pleasant results (according to my taste) for printing.
I guess I should have taken a look at the images with a VR viewer before posting... ;-)
By the way - anything new about my other problem with the project file I sent you?
Best regards from Berlin
Post Number: 315
|Posted on Friday, July 20, 2007 - 3:19 pm: |
Sorry about "dropping the ball" on your other problem. I will try to write a reply as soon as I can.