simple BSpline surfaces could not be exported

• To: mathgroup at smc.vnet.net
• Subject: [mg107561] simple BSpline surfaces could not be exported
• From: pratip <pratip.chakraborty at gmail.com>
• Date: Wed, 17 Feb 2010 07:02:21 -0500 (EST)

```Hallo Everybody,

Here is a disturbing problem with Mathematica's export functionality.
lets take this example points from which we make a nice spline
surface.
pts = {{{0.5, 0, -0.5}, {0, 0, -0.5}, {0, 1, -0.5}, {0.5,
1, -0.5}, {1, 1, -0.5}, {1, 0, -0.5}, {0.5, 0, -0.5}},
{{0.5, 0, 0.7}, {0, 0, 0.7}, {0, 1, 0.7}, {0.5, 1, 0.7}, {1, 1,
0.7}, {1, 0, 0.7}, {0.5, 0, 0.7}},
{{0.5, 0, 0.9}, {0, 0, 0.9}, {0, 1, 1.5}, {0.5, 1, 1.5}, {1, 1,
1.5}, {1, 0, 0.9}, {0.5, 0, 0.9}},
{{0.5, -0.1, 1}, {0, -0.1, 1}, {0, 3.5, 2}, {0.5, 0.5, 2}, {1,
3.5, 2}, {1, -0.1, 1}, {0.5, -0.1, 1}},
{{0.5, -0.3, 1}, {0, -0.3, 1}, {0, -.3, 2}, {0.5, -0.3,
2}, {1, -.3, 2}, {1, -0.3, 1}, {0.5, -0.3, 1}},
{{0.5, -1.5, 1}, {0, -1.5, 1}, {0, -1.5, 2}, {0.5, -1.5,
2}, {1, -1.5, 2}, {1, -1.5, 1}, {0.5, -1.5, 1}}}; w = {{1, .5, .5,
1, .5, .5, 1}, {1, .5, .5, 1, .5, .5, 1}, {1, .5, .5, 1, .5, .5,
1}, {1, .5, .5, 1, .5, .5, 1}, {1, .5, .5, 1, .5, .5,
1}, {1, .5, .5, 1., .5, .5, 1}};
uk = {0, 0, 0, 1/4, 1/2, 3/4, 1, 1, 1};
vk = {0, 0, 0, 1/4, 1/2, 1/2, 3/4, 1, 1, 1};

Lets make the BSpline surface and see it as a Mathematica Graphics3D
object.

pic=Graphics3D[{
BSplineSurface[pts, SplineKnots -> {uk, vk}, SplineDegree -> 2,
SplineWeights -> w, SplineClosed -> {False, True}]}]

Now when I try to export it in 3ds

Export["foil.3ds", pic];

or even if I try any other format

Export["foil.stl", pic];

I am always getting an error that reads.
"Export::nodta: Graphics3D contains no data that can be exported to
the 3DS format. >>"

Can anybody tell me how to get read of this. May be i am missing
something trivial.
I need to export this type of 3D geometry for further analysis and to