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.

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neodasa <klu### [at] nycrrcom> wrote:
> 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?

  For two adjacent bicubic patches to form a smooth surface the control
points in the shared edge must be equal, and the closest inner control
points of each patch, along with their correspondent edge control point,
must form a straight line.

-- 
                                                          - Warp

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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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John VanSickle <evi### [at] hotmailcom> wrote:
> 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.

  They don't have to be mid-way, as long as A02-AB0-B01 forms a straight
line, and likewise for the other trios.

-- 
                                                          - Warp

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These two images might help you see where you can place the control points:

   http://home.online.no/~t-o-k/POV-Ray_Images/Bezier_Patches_Stitched.jpg
   http://home.online.no/~t-o-k/POV-Ray_Images/Bezier_Patches_Stitched_.jpg


You can find some more Bezier patch stitching images here:

   http://home.online.no/~t-o-k/POV-Ray_Images

-- 
Tor Olav
http://subcube.com

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