PanoTools:
Re: {HTML} suggestions for new projections
JD Smith 2004-May-20 23:21:08
On Thu, 2004-05-20 at 13:36, rjlittlefield wrote:
> For static prints of partial panos, it would also be good to have
> shape-preserving projections. ("Conformal" is the magic word.)
>
> These preserve shape (locally) by always stretching vertical and
> horizontal differentials by the same amount.
>
> The classic Mercator is a conformal cylindrical projection. It would
> be good for typical horizontal panos.
Of course maps cannot be both conformal and area-preserving, so it's
always a trade-off (do you want the shape or the size of objects to look
correct as you move away from the map center?). Some projections are
neither conformal nor area-preserving, but attempt to split the
difference in errors between them.
> I would also like to have transverse cylindrical projections for
> vertical panos. Currently I make vertical panos by rotating source
> images 90 degrees, rendering a traditional cylindrical projection,
> then rotating the rendered pano back to vertical. It works, it's
> just awkward.
Yes, agreed. In fact arbitrary oblique cylindrical projections are also
interesting, though actually taking one would be a challenge. I wonder
if a general purpose projection library (like the General Cartographic
Transformation Package) would be useful to roll into the PanoTools
source. Has a lot of overkill (various earth coordinate datum sets,
etc.) but might save the trouble of implementing all of the various
projections (and their inverses) in numerically robust ways. Here's a
blurb:
The General Cartographic Transformation Package (GCTP) is a system of
software routines designed to permit the transformation of coordinate
pairs from one map projection to another. The GCTP is the standard
computer software used by the National Mapping Division for map
projection computations.
Not sure about license issues, but it has been included in commercial
products.
JD
> Refs:
> http://mathworld.wolfram.com/ConformalProjection.html
> http://mathworld.wolfram.com/MercatorProjection.html
>
> --- In #removed#, JD Smith <#removed#> wrote:
> > I'd actually like to see someday an area-preserving projection for
> full
> > 360x180 panoramas, like the Lambert cylindrical equal-area
> projection,
> > which I think would look nicer than straight cylindrical (which is
> > rarely used in map projections).
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