[Mapserver-users] rubber sheeting

[Pericles S. Nacionales]

Jan,

You can look at Michael Gourlay's Xmorph program.  His web site is at
http://www.colorado-research.com/~gourlay/software/Graphics/Xmorph/. 
Perhaps not exactly what you're looking for but there might be useful
information on the web site.

-Perry


On Sat, 2003-07-19 at 05:51, Jan Hartmann wrote:
> Yes, that is the answer. I hadn't realized that it was done by 
> triangulation and that morphing is just another name for rubber 
> sheeting. Both are very well known technologies, I just hadn't made the 
> link to GIS terminology. Gives me quite a lot of good technical 
> pointers. If anyone knows free software or source code in these two 
> areas that could be easily transferred to GIS, please let me know. I 
> could try to implement it in GRASS or GDAL
> 
> Thanks Franck, Norman
> 
> Jan
> 
> Franck Martin wrote:
> > Many raster software offer polynomial rectification which highly 
> > inadequate in most of cases today. Rubber Sheeting is the answer and the 
> > correct term in GIS, and as described below it is based on a 
> > triangulation of the map to be modified..
> > 
> > The difference between polynomial and rubber sheeting is that rubber 
> > sheeting needs more ground control points.
> > 
> > GRASS does not offer rubber sheeting, it is a pity as I don't know any 
> > free software that offers it.
> > 
> > I guess the algorithm for rubber sheeting is well known or known also 
> > under the name morphing.. A google search should give some results here...
> > 
> > Cheers
> > 
> > 
> > 
> > On Sat, 2003-07-19 at 04:43, Norman Vine wrote:
> > 
> >>/Jan Hartmann writes:
> >>> 
> >>> 
> >>> The problem is that AFAIK all these rectifying routines are computed 
> >>> globally. You can use of course a higher order polynomial, but even so 
> >>> the placement of every control point will affect the whole map. 
> >>> Moreover, you can't use very high polynomials and too many control 
> >>> points. What I am looking for is something that will do *local* 
> >>> transformations based on nearby control points, and stretch the results 
> >>> together some way. Those old maps are generally correct on small 
> >>> subregions, but the subregions fit in no way together. There is 
> >>> certainly no numerical soluton for it.
> >>
> >>Good question, 
> >>I don't think I have ever thought about 'locally adaptive' rubber sheeting.
> >>
> >>Probably easiest to do by separating out the U and V correction
> >>
> >>A 'simplistic' method might be to make two countour 'grids', for testing 
> >>purposes you could use simple triangulated surfaces, where 'Z'  was the 
> >>displacement in X or Y respectively of each control point.  Then by 
> >>queryng the grids by the original {X,Y} you would get a {U,V} offset by 
> >>interpolation, that can be used to determine the new coordinates.  
> >>One trick here is that the new image wants to be constructed by triangles
> >>and not points, think texture mapping
> >>
> >>< tough todo with ASCII >
> >>*  *   *   *
> >>| \ | \ | \ |
> >>*  *  *   *
> >>| \ | \ | \ |
> >>*  *   *   *
> >>
> >>HTH
> >>
> >>Norman
> >>_______________________________________________/
> >>
> > 
> > -- 
> > Franck Martin <franck at sopac.org <mailto:franck at sopac.org>>
> > SOPAC
> > 
> > 
> 
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-- 
Pericles S. Nacionales <nacional at cbs.umn.edu>
University of Minnesota