[vtkusers] re: Try again - merging

[Jared Cohen]

Well, I tried using the offset, and the back-and-forth transform series. 
But once it passed through the CleanPolyData filter, it STILL gave me 
the band-o'-crap down the side. I'm starting to reach the same 
conclusion that I had reached the last time I tried this -- namely, that 
merging the points just isn't worth the headache. ;-)

Sean McInerney wrote:

> 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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