/// <summary>
/// Constructs a nurbs curve representation of this polyline.
/// </summary>
/// <returns>A Nurbs curve shaped like this polyline.</returns>
private void ToNurbs()
{
double lengthSum = 0;
List <double> weights = new List <double>();
KnotVector knots = new KnotVector {
0, 0
};
List <Point4> ctrlPts = new List <Point4>();
for (int i = 0; i < ControlPointLocations.Count - 1; i++)
{
lengthSum += Segments[i].Length;
knots.Add(lengthSum);
weights.Add(1.0);
ctrlPts.Add(new Point4(ControlPointLocations[i], 1.0));
}
knots.Add(lengthSum);
weights.Add(1.0);
ctrlPts.Add(new Point4(ControlPointLocations.Last(), 1.0));
Weights = weights;
Knots = knots.Normalize();
Degree = 1;
ControlPoints = ctrlPts;
}
/// <summary>
/// Computes the knot vectors used to calculate a curve global interpolation.
/// </summary>
private static KnotVector ComputeKnotsForInterpolation(List <double> curveParameters, int degree, bool hasTangents)
{
// Start knot vectors.
KnotVector knots = CollectionHelpers.RepeatData(0.0, degree + 1).ToKnot();
// If we have tangent values we need two more control points and knots.
int start = (hasTangents) ? 0 : 1;
int end = (hasTangents) ? curveParameters.Count - degree + 1 : curveParameters.Count - degree;
// Use averaging method (Eqn 9.8) to compute internal knots in the knot vector.
for (int i = start; i < end; i++)
{
double weightSum = 0.0;
for (int j = 0; j < degree; j++)
{
weightSum += curveParameters[i + j];
}
knots.Add((1.0 / degree) * weightSum);
}
// Add end knot vectors.
knots.AddRange(CollectionHelpers.RepeatData(1.0, degree + 1));
return(knots);
}
/// <summary>
/// Computes the knots vectors used to calculate an approximate curve.
/// </summary>
private static KnotVector ComputeKnotsForCurveApproximation(List <double> curveParameters, int degree, int numberOfCtrPts, int numberOfPts)
{
// Start knot vectors.
KnotVector knots = CollectionHelpers.RepeatData(0.0, degree + 1).ToKnot();
// Compute 'd' value - Eqn 9.68.
double d = (double)numberOfPts / (numberOfCtrPts - degree);
// Find the internal knots - Eqn 9.69.
for (int j = 1; j < numberOfCtrPts - degree; j++)
{
int i = (int)(j * d);
double alpha = (j * d) - i;
double knot = ((1.0 - alpha) * curveParameters[i - 1]) + (alpha * curveParameters[i]);
knots.Add(knot);
}
// Add end knot vectors.
knots.AddRange(CollectionHelpers.RepeatData(1.0, degree + 1));
return(knots);
}
/// <summary>
/// Reduce the degree of a NURBS curve.
/// </summary>
/// <param name="curve">The object curve to elevate.</param>
/// <param name="tolerance">Tolerance value declaring if the curve is degree reducible.</param>
/// <returns>The curve after degree reduction, the curve will be degree - 1 from the input.</returns>
internal static NurbsBase ReduceDegree(NurbsBase curve, double tolerance)
{
int n = curve.Knots.Count - curve.Degree - 2;
int p = curve.Degree;
KnotVector U = curve.Knots;
List <Point4> Qw = curve.ControlPoints;
// local arrays.
Point4[] bpts = new Point4[p + 1];
Point4[] nextbpts = new Point4[p - 1];
Point4[] rbpts = new Point4[p];
double[] alphas = new double[p - 1];
// Output values;
List <Point4> Pw = new List <Point4>();
KnotVector Uh = new KnotVector();
// Initialize some variables.
int ph = p - 1;
int mh = ph;
int kind = ph + 1;
int r = -1;
int a = p;
int b = p + 1;
int m = n + p + 1;
Pw.Add(Qw[0]);
// Compute left end of knot vector.
for (int i = 0; i <= ph; i++)
{
Uh.Add(U[0]);
}
// Initialize first Bezier segment.
for (int i = 0; i <= p; i++)
{
bpts[i] = Qw[i];
}
// Initialize error vector.
Vector e = Vector.Zero1d(m);
// Loop through the knot vector.
while (b < m)
{
// First compute knot multiplicity.
int i = b;
while (b < m && Math.Abs(U[b] - U[b + 1]) < GSharkMath.Epsilon)
{
b += 1;
}
int mult = b - i + 1;
mh = mh + mult - 1;
int oldr = r;
r = p - mult;
// Insert knot U[b] r times.
// Checks for integer arithmetic.
int lbz = (oldr > 0) ? (int)Math.Floor((double)((oldr + 2) / 2)) : 1;
if (r > 0)
{
// Inserts knot to get Bezier segment.
double numer = U[b] - U[a];
for (int k = p; k > mult; k--)
{
alphas[k - mult - 1] = numer / (U[a + k] - U[a]);
}
for (int j = 1; j <= r; j++)
{
int save = r - j;
int s = mult + j;
for (int k = p; k >= s; k--)
{
bpts[k] = (bpts[k] * alphas[k - s]) + (bpts[k - 1] * (1.0 - alphas[k - s]));
}
nextbpts[save] = bpts[p];
}
}
// Degree reduce Bezier segment.
double maxError = BezierDegreeReduce(bpts, p, out rbpts);
e[a] += maxError;
if (e[a] > tolerance)
{
throw new Exception("Curve not degree reducible");
}
// Remove knot U[a] oldr times.
if (oldr > 0)
{
// Must remove knot u=U[a] oldr times.
int first = kind;
int last = kind;
for (int k = 0; k < oldr; k++)
{
// Knot removal loop.
int l = first;
int j = last;
int kj = j - kind;
while (j - l > k)
{
double alfa = (U[a] - Uh[l - 1]) / (U[b] - Uh[l - 1]);
double beta = (U[a] - Uh[j - k - 1]) / (U[b] - Uh[j - k - 1]);
Pw[l - 1] = (Pw[l - 1] - Pw[l - 2] * (1.0 - alfa)) / alfa;
rbpts[kj] = (rbpts[kj] - rbpts[kj + 1] * beta) / (1.0 - beta);
l += 1;
j -= 1;
kj -= 1;
}
// Compute knot removal error bounds (Br).
double Br;
if (j - l < k)
{
Br = Pw[l - 2].DistanceTo(rbpts[kj + 1]);
}
else
{
double delta = (U[a] - Uh[l - 1]) / (U[b] - Uh[l - 1]);
Point4 A = (rbpts[kj + 1] * delta) + (Pw[l - 2] * (1.0 - delta));
Br = Pw[l - 1].DistanceTo(A);
}
// Update the error vector.
int K = a + oldr - k;
int q = (int)Math.Floor((double)(2 * p - k + 1) / 2);
int L = K - q;
for (int ii = L; ii <= a; ii++)
{
// These knot vectors were effected.
e[ii] += Br;
if (e[ii] > tolerance)
{
throw new Exception("Curve not degree reducible");
}
}
first -= 1;
last += 1;
}
}
// Load knot vector and control points.
if (a != p)
{
// Load the knot ua.
for (int j = 0; j < ph - oldr; j++)
{
Uh[kind] = U[a];
kind += 1;
}
}
for (int j = lbz; j <= ph; j++)
{
// Load control points into Qw.
Pw.Add(rbpts[j]);
}
if (b < m)
{
// Set up for the next pass thru loop.
for (int j = 0; j < r; j++)
{
bpts[j] = nextbpts[j];
}
for (int j = r; j <= p; j++)
{
bpts[j] = Qw[b - p + j];
}
a = b;
b += 1;
}
else
{
// End knot.
for (int j = 0; j <= ph; j++)
{
Uh.Add(U[b]);
}
}
}
return(new NurbsCurve(p - 1, Uh, Pw));
}
/// <summary>
/// Elevates the degree of a curve.
/// <em>Implementation of Algorithm A5.9 of The NURBS Book by Piegl and Tiller.</em>
/// </summary>
/// <param name="curve">The object curve to elevate.</param>
/// <param name="finalDegree">The expected final degree. If the supplied degree is less or equal the curve is returned unmodified.</param>
/// <returns>The curve after degree elevation.</returns>
internal static NurbsBase ElevateDegree(NurbsBase curve, int finalDegree)
{
if (finalDegree <= curve.Degree)
{
return(curve);
}
int n = curve.Knots.Count - curve.Degree - 2;
int p = curve.Degree;
KnotVector U = curve.Knots;
List <Point4> Pw = curve.ControlPoints;
int t = finalDegree - curve.Degree; // Degree elevate a curve t times.
// local arrays.
double[,] bezalfs = new double[p + t + 1, p + 1];
Point4[] bpts = new Point4[p + 1];
Point4[] ebpts = new Point4[p + t + 1];
Point4[] nextbpts = new Point4[p - 1];
double[] alphas = new double[p - 1];
int m = n + p + 1;
int ph = finalDegree;
int ph2 = (int)Math.Floor((double)(ph / 2));
// Output values;
List <Point4> Qw = new List <Point4>();
KnotVector Uh = new KnotVector();
// Compute Bezier degree elevation coefficients.
bezalfs[0, 0] = bezalfs[ph, p] = 1.0;
for (int i = 1; i <= ph2; i++)
{
double inv = 1.0 / GSharkMath.GetBinomial(ph, i);
int mpi = Math.Min(p, i);
for (int j = Math.Max(0, i - t); j <= mpi; j++)
{
bezalfs[i, j] = inv * GSharkMath.GetBinomial(p, j) * GSharkMath.GetBinomial(t, i - j);
}
}
for (int i = ph2 + 1; i <= ph - 1; i++)
{
int mpi = Math.Min(p, i);
for (int j = Math.Max(0, i - t); j <= mpi; j++)
{
bezalfs[i, j] = bezalfs[ph - i, p - j];
}
}
int mh = ph;
int kind = ph + 1;
int r = -1;
int a = p;
int b = p + 1;
int cind = 1;
double ua = U[0];
Qw.Add(Pw[0]);
for (int i = 0; i <= ph; i++)
{
Uh.Add(ua);
}
// Initialize first Bezier segment.
for (int i = 0; i <= p; i++)
{
bpts[i] = Pw[i];
}
// Big loop thru knot vector.
while (b < m)
{
int i = b;
while (b < m && Math.Abs(U[b] - U[b + 1]) < GSharkMath.Epsilon)
{
b += 1;
}
int mul = b - i + 1;
mh = mh + mul + t;
double ub = U[b];
int oldr = r;
r = p - mul;
// Insert knot U[b] r times.
// Checks for integer arithmetic.
int lbz = (oldr > 0) ? (int)Math.Floor((double)((2 + oldr) / 2)) : 1;
int rbz = (r > 0) ? (int)Math.Floor((double)(ph - (r + 1) / 2)) : ph;
if (r > 0)
{
// Inserts knot to get Bezier segment.
double numer = ub - ua;
for (int k = p; k > mul; k--)
{
alphas[k - mul - 1] = (numer / (U[a + k] - ua));
}
for (int j = 1; j <= r; j++)
{
int save = r - j;
int s = mul + j;
for (int k = p; k >= s; k--)
{
bpts[k] = Point4.Interpolate(bpts[k], bpts[k - 1], alphas[k - s]);
}
nextbpts[save] = bpts[p];
}
}
// End of insert knot.
// Degree elevate Bezier.
for (int j = lbz; j <= ph; j++)
{
ebpts[j] = Point4.Zero;
int mpi = Math.Min(p, j);
for (int k = Math.Max(0, j - t); k <= mpi; k++)
{
ebpts[j] += bpts[k] * bezalfs[j, k];
}
}
if (oldr > 1)
{
// Must remove knot u=U[a] oldr times.
int first = kind - 2;
int last = kind;
double den = ub - ua;
double bet = (ub - Uh[kind - 1]) / den;
for (int tr = 1; tr < oldr; tr++)
{
// Knot removal loop.
int ii = first;
int jj = last;
int kj = jj - kind + 1;
while (jj - ii > tr)
{
// Loop and compute the new control points for one removal step.
if (ii < cind)
{
double alf = (ub - Uh[ii]) / (ua - Uh[ii]);
Qw.Add(Point4.Interpolate(Qw[ii], Qw[ii - 1], alf));
}
if (jj >= lbz)
{
if (jj - tr <= kind - ph + oldr)
{
double gam = (ub - Uh[jj - tr]) / den;
ebpts[kj] = Point4.Interpolate(ebpts[kj], ebpts[kj + 1], gam);
}
else
{
ebpts[kj] = Point4.Interpolate(ebpts[kj], ebpts[kj + 1], bet);
}
}
ii += 1;
jj -= 1;
kj -= 1;
}
first -= 1;
last += 1;
}
}
// End of removing knot, n = U[a].
if (a != p)
{
// Load the knot ua.
for (int j = 0; j < ph - oldr; j++)
{
Uh.Add(ua);
}
}
for (int j = lbz; j <= rbz; j++)
{
// Load control points into Qw.
Qw.Add(ebpts[j]);
}
if (b < m)
{
// Set up for the next pass thru loop.
for (int j = 0; j < r; j++)
{
bpts[j] = nextbpts[j];
}
for (int j = r; j <= p; j++)
{
bpts[j] = Pw[b - p + j];
}
a = b;
b += 1;
ua = ub;
}
else
{
// End knot.
for (int j = 0; j <= ph; j++)
{
Uh.Add(ub);
}
}
}
return(new NurbsCurve(finalDegree, Uh, Qw));
}
