[Mapserver-users] rubber sheeting

[Paul Ramsey]

The JUMP/JCS toolkit in Java land has some rubber sheeting built into 
it. We never implemented full thin-plate spines (one of our advisors 
favourite algorithms) but there is some good local warping in there.
P.

On Saturday, July 19, 2003, at 06:10 AM, woodbri at swoodbridge.com wrote:

> Jan,
>
> I think section 3.3 is the algorithm you want at:
>   http://www.hammerhead.com/thad/morph.html
>
> It is based on lines not points, but when you read the algorithm it
> will make sense.
>
> -Steve W.
>
> On 19 Jul 2003 at 12:51, 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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>
>
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      Paul Ramsey
      Refractions Research
      Email: pramsey at refractions.net
      Phone: (250) 885-0632