Flat Panel Panoramic Stretching
Ed
client and because there was no other way to capture the views they
wanted, I shot with my panoramic rig, using an EOS 24mm shift lens
because of needing the up/down flexibility. The proofs have stitched
together wonderfully ("Heavy + shift" setting) with no seam issues at
all, but in rectilinear mode, the sides stretch and distort a great
deal. Windows and doors are greatly elongated as is the overall width
of the shot. Switching over to cylindrical, the distortion is all but
eliminated, however features like seat rows and ceiling seams and
soffits are rendered as arcs instead of straight lines. Am I missing
an adjustment check-off or a setting somewhere? Thanks.
PTGui Support
You're running into the limits of physics: the stretching is necessary
to keep straight lines straight. The effect is noticable in any wide
angle image but becomes stronger with wider field of view.
See 5.1:
http://www.ptgui.com/support.html#5_1
And:
http://www.ptgui.com/man/projections.html
Further, using a shift lens is not necessary, you could have achieved
the same result using a normal lens and tilting the camera, see 2.19:
http://www.ptgui.com/support.html#2_19
Joost
Erik Krause
> Good Afternoon: I'm working on a number of interior views for a
> client and because there was no other way to capture the views they
> wanted, I shot with my panoramic rig, using an EOS 24mm shift lens
> because of needing the up/down flexibility.
No need to use a shift lens. As long as you rotate (tilt) around the
no-parallax-point you can point your lens up or down as you like.
Perspective will be corrected during stitching.
> The proofs have stitched
> together wonderfully ("Heavy + shift" setting) with no seam issues at
> all, but in rectilinear mode, the sides stretch and distort a great
> deal. Windows and doors are greatly elongated as is the overall width
> of the shot.
This is the very nature of the rectilinear projection. This is the same
like for an ultra wide angle lens. Maximum angle that can be displayed
in rectilinear is between 100� and 140� depending on the subject. 160�
usually gives you heavy distortions.
> Switching over to cylindrical, the distortion is all but
> eliminated, however features like seat rows and ceiling seams and
> soffits are rendered as arcs instead of straight lines.
Again this is the very nature of cylindrical projection. The lines would
look right if you where in the center of a cylinder formed by the image.
For any other point of view (or if you unroll the cylinder) the lines
get bent.
More on projections: http://wiki.panotools.org/Projections
> Am I missing an adjustment check-off or a setting somewhere?
No. There is no way to have an undistorted flat image from the world
surrounding you. You can't flatten a sphere undistorted. It's less
pronounced in telephoto shots, it's visible in wide angle shots and it
gets severe in very wide panoramas.
However, there are ways to trick the brain in believing there is no (or
little) distortion. If you have a vantage point in the center of your
image try vedutismo and play with the settings.
--
Erik Krause
http://www.erik-krause.de
Ed
Appreciate the info. Thought I might be pushing it a bit by trying to
capture a little more than 90 degrees and attempting to avoid all the
"push back" inherent in wide angle optics. Erik, thanks for the
Vedutismo suggestion. For a couple of the shots, it definitely looks
better than the rectilinear. Many thanks.
Ed
Erik Krause
> Erik, thanks for the
> Vedutismo suggestion. For a couple of the shots, it definitely looks
> better than the rectilinear.
Yes, it's a great possibility worth to keep in mind when shooting. There
are occasions where you don't see any distortions and have a very wide
angle.
It is interesting that this old projection - it was used by 18th century
painters - was mathematically reconstructed only few years ago by
members of the panotools community: http://vedutismo.net/
See also http://vedutismo.net/Pannini/
http://wiki.panotools.org/The_General_Panini_Projection
Kelly
@ Ed - From following Erik's link, this also looked like it might be
worth further investigation:
http://wiki.panotools.org/The_General_Panini_Projection
Kelly
Joergen Geerds
I hope Joost will forgive me for this, but you can also look at the
alternate projection methods that Max Lyon's PTAssembler has to offer:
http://www.tawbaware.com/projections.htm
Joergen
newyorkpanorama.com