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### Create NURBS Surface

Demonstrates how to create a NURBS surface.

C/C++

static bool CreateSurfacesExample( CRhinoDoc& doc )
{
const int bIsRational = false;
const int dim = 3;
const int u_degree = 2;
const int v_degree = 3;
const int u_cv_count = 3;
const int v_cv_count = 5;

// The knot vectors do NOT have the 2 superfluous knots
// at the start and end of the knot vector.  If you are
// coming from a system that has the 2 superfluous knots,
// just ignore them when creating NURBS surfaces.
double u_knot[ u_cv_count + u_degree - 1 ];
double v_knot[ v_cv_count + v_degree - 1 ];

// make up a quadratic knot vector with no interior knots
u_knot[0] = u_knot[1] = 0.0;
u_knot[2] = u_knot[3] = 1.0;

// make up a cubic knot vector with one simple interior knot
v_knot[0] = v_knot[1] = v_knot[2] = 0.0;
v_knot[3] = 1.5;
v_knot[4] = v_knot[5] = v_knot[6] = 2.0;

// Rational control points can be in either homogeneous
// or euclidean form. Non-rational control points do not
// need to specify a weight.
ON_3dPoint CV[u_cv_count][v_cv_count];

int i, j;
for ( i = 0; i < u_cv_count; i++ ) {
for ( j = 0; j < v_cv_count; j++ ) {
CV[i][j].x = i;
CV[i][j].y = j;
CV[i][j].z = i-j;
}
}

ON_NurbsSurface nurbs_surface( dim, bIsRational,
u_degree+1, v_degree+1,
u_cv_count, v_cv_count );

for ( i = 0; i < nurbs_surface.KnotCount(0); i++ )
nurbs_surface.SetKnot( 0, i, u_knot[i] );

for ( j = 0; j < nurbs_surface.KnotCount(1); j++ )
nurbs_surface.SetKnot( 1, j, v_knot[j] );

for ( i = 0; i < nurbs_surface.CVCount(0); i++ ) {
for ( j = 0; j < nurbs_surface.CVCount(1); j++ ) {
nurbs_surface.SetCV( i, j, CV[i][j] );
}
}

bool ok = false;
if ( nurbs_surface.IsValid() )
{