POV-Ray : Newsgroups : povray.general : The seam of two bi-cubic patches isn't smooth when raised : Re: The seam of two bi-cubic patches isn't smooth when raised Server Time
30 Jul 2024 08:20:28 EDT (-0400)
  Re: The seam of two bi-cubic patches isn't smooth when raised  
From: John VanSickle
Date: 17 May 2009 20:30:55
Message: <4a10ac3f$1@news.povray.org>
neodasa wrote:
> I followed the instructions for joining the two (blue and white, red and white)
> patches.  I made sure the coordinates for the forth column of the blue patch:
> 
> B14
> B24
> B34
> B44
> 
> were the same as the coordinates for the first column of the red patch:
> 
> R11
> R21
> R31
> R41
> 
> and then added:
> 
> #declare R12=B14+(B14-B13);
> #declare R22=B24+(B24-B23);
> #declare R32=B34+(B34-B33);
> #declare R42=B44+(B44-B43);
> 
> as per the instruction to smooth out the seam, but when I tested a control point
> and raised the seam, it appeared as a sharp edge rather than a smooth edge,
> which is what it's not suppose to do.  Anyone know why this happened?
> 
> Thanks.

You have two patches, sharing control points along the edge where they 
meet, as such:

A00---A01---A02---AB0---B01---B02---B03
  |     |     |     |     |     |     |
A10---A11---A12---AB1---B11---B12---B13
  |     |     |     |     |     |     |
A20---A21---A22---AB2---B21---B22---B23
  |     |     |     |     |     |     |
A30---A31---A32---AB3---B31---B32---B33

In order for the patches to meet smoothly, AB0 must mid-way between A02 
and B01, AB1 must be mid-way between A12 and B11, AB2 must be mid-way 
between A22 and B21, and AB3 must be mid-way between A32 and B31.

Hope this helps,
John


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