[vtkusers] re: Try again - merging

[Sean McInerney]

Jared,

   You'll notice that the band of crap on your sphere is actually your 
entire texture mirror mapped onto that single strip of polygons ... not 
just from the center as I said previously ... unless that strip is 1 
pixel wide ;-)

-Sean

Sean McInerney wrote:
> Hi Jared,
> 
>   Actually, I think that I do understand your problem. If you merge the 
> non-polar points along the edges of the plane mapped to the sphere, what 
>  are the texture coordinates of those points? Get it? Before the merge, 
> they're zero (0) on one side, one (1) on the other. After the merge, you 
> are getting an interpolation between 0 and 1 / thetaRes - 1 (i.e. some 
> crap from the center of your image being placed along that border). 
> Furthermore, by using the offsetting that I suggest, as well as going 
> back and forth with the transform, you'll avoid having a black hole at 
> the north pole (you'll see what I mean). The bottom line is that, for 
> you, the only points worth merging are probably the poles. Even then, 
> you'll end up with texture artifact that won't show up with merging.
> 
>   So, this doesn't solve the *grand* merging debate, but it may solve 
> yours ;-)
> 
> -Sean
> 
> Jared Cohen wrote:
> 
>> Thanks, but I don't think you understand the problem. I can close the 
>> gap just fine, but the two edges will overlap without being merged 
>> together. It's when I merge them using a CleanPolyData filter that I 
>> get the warping effect.
>>
>>
>>
>>> Hi Jared,
>>>
>>>   I have some C++ code based on the spherical Tcl example that I 
>>> think solves your problem. It avoids a singularity at the Z axis by 
>>> offsetting the plane by a very small amount. I am attaching the 
>>> source file 'spherical.cxx'. It takes any valid 2D vtkImageReader2 
>>> input and maps it to a sphere in the manner that you describe.
>>>
>>> The Cmake configuration stuff is as follows:
>>>
>>> ADD_EXECUTABLE (spherical spherical.cxx)
>>> TARGET_LINK_LIBRARIES (spherical vtkRendering vtkIO vtkGraphics)
>>>
>>> -Sean
>>>
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