On Sat, Sep 26, 2009 at 4:18 PM, D M German <dmg@...> wrote:
> Thomas> Hi Jim,
> Thomas> I'd say the floor example is aligned as well as could be
> Thomas> expected with just a tilt and shift. Or has the magnification
> Thomas> (or Z distance) been optimized too?
> Shear also. tried shear with the Tr model, but didn't work.
> I am being confused by the optimizer. I can't get the Tr parameters to
> stay within reasonable values and still get good results.
> Thomas> Anyhow, to do much better would probably require lens
> Thomas> calibration, and some higher order corrections.
> Thinking about corrections, how many parameters do you need for your
If you mean correcting the lens projection, not more than 8. That counts
the projection type as a parameter, along with focal length, 3 or 4
"distortion" parameters, and the center shifts.. On this accounting libpano
presently uses 7 parameters: projection type, fov, a, b, c, d, e. For
lensFunc, there need to be new projection types that explicitly mean
"rectilinear lens", and one or more kinds of "fisheye lens". The use of
these codes would imply the use of 3 or 4 lensFunc-style distortion
parameters, one or two for a mathematical model of the lens and 2 or 3 for a
correction polynomial. The meaning of fov and center shifts would remain
It might be possible to get the number of distortion parameters down to 3,
which would be preferable from the statistical point of view, if they were
to be optimized at stitching time. However the basic idea of lens
calibration is to predetermine some lens parameters rather than optimizing
them at each stitch, one big benefit of which is to reduce the number of
parameters that need to be estimated from the control points. I don't think
it is realistic to stop optimizing fov or center shifts, and maybe one
adjustable shape parameter should be provided for stitching, but that could
be different from any of the calibration parameters. My thinking is that
some adjustable stretching -- like morph-to-fit -- is likely to be better at
fitting images together than fiddling with the lens parameters.
> Thomas> Ultimately, the nadir matching problem needs 3D depth analysis
> Thomas> and some "orthophoto"-type local adjustments. Perhaps we
> Thomas> should think seriously about reviving morph-to-fit?
> I worked on that long time ago. I think I can get it working again.
> Daniel M. German
> dmg (at) uvic (dot) ca
> replace (at) with @ and (dot) with .