PanoTools:
Re: Re: Long time lurker with 1DS pano questions > ACTUALLY precision heads.
Julian 2006-Mar-09 00:41:54
Thanks Yuval, Hans and Kevin, I THINK I now get it, as follows...
If you take full VR type panos with very wide angle lenses, then a small
error in camera pointing angle (Hans uses 0.05degrees) translates to only a
pixel or two error in your stitched output so you can use a good precision
head and create a good pano without any use of control points at all. Just
use a project-type file to tell the software the location of the images and
the characteristics of the lenses and the software "blindly" stitches it
together. No CPs needed, and you can conveniently batch process. Also
the verticals are vertical just because you set up the camera accurately.
If you take what I will call higher resolution panos with not so wide angle
lenses then even the small errors from a precision head would lead to
unacceptable inaccuracies at the joins if you didn't use control points to
fine tune the stitching (same angular error > greater error in terms of
pixels - see my example below). So you need control points - either manual
or using an auto CP generator. But you can still do "automatic" panos if
you use the auto CP generator now integrated into PTGui and other software,
and if there are enough of the right kind of features in each image for the
auto CP generator to work properly.
Once you decide you are going to rely on an auto CP generator, then (NOT
counting parallax problems) you don't need any accurate camera pointing at
all, so you can use any old head, or do hand held, and it doesn't make any
difference - the software works out which image goes where and how to align
them and how to warp them and how to stitch them. This is what I do now.
When there are closer objects that cause parallax errors I use a cheap,
non-precision head to give me nodal point rotation and so avoid
parallax. Probably you should include some manual vertical CPs if you
want accurate verticals, although in my type of panos I rarely notice this
is a problem.
So the advantage of a precision head for what I have called "high res
panos" is not that great? You would still need to establish some CPs since
(if I do my maths right) using a 60mm lens on my camera is about 140 pixels
per degree, so the .05degree accuracy of a precision head -> around 7
pixels of possible misalignment: too much without fine tuning the overlap
using CPs. And since you have to use CPs at all, it then doesn't really
matter how accurate your images are aligned any more. (Except that I guess
your verticals would be vertical without any further work).
But for wide angles as used in VR type work this same error is only 1 or 2
pixels, so ... no CPs needed at all.
Precision heads also have the advantage that even for "hi-res" panos, the
images would be loaded into your software by template to ALMOST the correct
position, so doing manual CPs would be very easy and might even be
faster/better than auto. With my very non-precision system, manual CPs are
a pain in the *rse.
If I have got that right, then thanks very much for the useful input.
Julian
At 12:01 AM 9/03/06, you wrote:
>On Mar 8, 2006, at 4:30 AM, Julian wrote:
> > What I don't understand is this - are
> > you saying that the pin-registered systems allowed you to stitch
> > the shots
> > "blindly" so that seams and mis-registration were invisible?
> >
>
>That is the whole premise behind the 360Precision head. Set it and
>forget it. All you have to do is check out the 360Precision forum to
>see there are a lot of satisfied customers:
>
>http://forum.360precision.com/360/forum/
>
>An advantage precision heads have is they will not fail should there
>be no features between a pair of images that would lend itself to a
>control point such as clear blue sky, etc. In those cases you would
>need to manually set the image position whereas if you had a
>template, the image is already in position.
>
>Kevin
>
>
>
>Yahoo! Groups Links
>
>
>
>
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