/// <summary>
/// Builds the coefficient matrix used to calculate a curve global interpolation.
/// </summary>
private static Matrix BuildCoefficientsMatrix(List <Point3> pts, int degree, bool hasTangents, List <double> curveParameters, KnotVector knots)
{
int dim = (hasTangents) ? pts.Count + 1 : pts.Count - 1;
Matrix coeffMatrix = new Matrix();
int dimEnd = (hasTangents) ? pts.Count - (degree - 1) : pts.Count - (degree + 1);
foreach (double u in curveParameters)
{
int span = knots.Span(dim, degree, u);
List <double> basicFunction = Evaluate.Curve.BasisFunction(degree, knots, span, u);
List <double> startRow = CollectionHelpers.RepeatData(0.0, span - degree);
List <double> endRow = CollectionHelpers.RepeatData(0.0, dimEnd - (span - degree));
coeffMatrix.Add(startRow.Concat(basicFunction).Concat(endRow).ToList());
}
if (!hasTangents)
{
return(coeffMatrix);
}
List <double> zeros = CollectionHelpers.RepeatData(0.0, coeffMatrix[0].Count - 2);
List <double> tangent = new List <double> {
-1.0, 1.0
};
coeffMatrix.Insert(1, tangent.Concat(zeros).ToList());
coeffMatrix.Insert(coeffMatrix.Count - 1, zeros.Concat(tangent).ToList());
return(coeffMatrix);
}
/// <summary>
/// Bezier degree reduction.
/// <em>Refer to The NURBS Book by Piegl and Tiller at page 220.</em>
/// </summary>
private static double BezierDegreeReduce(Point4[] bpts, int degree, out Point4[] rbpts)
{
// Eq. 5.40
int r = (int)Math.Floor(((double)degree - 1) / 2);
Point4[] P = new Point4[degree];
P[0] = bpts[0];
P[P.Length - 1] = bpts.Last();
bool isDegreeOdd = degree % 2 != 0;
int r1 = (isDegreeOdd) ? r - 1 : r;
// Eq. 5.41
for (int i = 1; i <= r1; i++)
{
double alphaI = (double)i / degree;
P[i] = (bpts[i] - (P[i - 1] * alphaI)) / (1 - alphaI);
}
for (int i = degree - 2; i >= r + 1; i--)
{
double alphaI = (double)(i + 1) / degree;
P[i] = (bpts[i + 1] - (P[i + 1] * (1 - alphaI))) / alphaI;
}
/* Equations (5.43) and (5.44) express the parametric error {distance between points at corresponding parameter values);
* the maximums of geometric and parametric errors are not necessarily at the same u value.
* For p even the maximum error occurs at u = 1/2; for p odd the error is zero at u = 1/2, and it has two peaks a bit to the left and
* right of u = 1/2. */
// Eq. 5.43 p even.
KnotVector knots = new KnotVector(degree - 1, P.Length);
int span = knots.Span(degree - 1, 0.5);
List <double> Br = Evaluate.Curve.BasisFunction(degree - 1, knots, span, 0.5);
double parametricError = bpts[r + 1].DistanceTo((P[r] + P[r + 1]) * 0.5) * Br[r + 1];
// Eq. 5.42
if (isDegreeOdd)
{
double alphaR = (double)r / degree;
Point4 PLeft = (bpts[r] - (P[r - 1] * alphaR)) / (1 - alphaR);
double alphaR1 = (double)(r + 1) / degree;
Point4 PRight = (bpts[r + 1] - (P[r + 1] * (1 - alphaR1))) / alphaR1;
P[r] = (PLeft + PRight) * 0.5;
// Eq. 5.44 p odd.
parametricError = ((1 - alphaR) * 0.5) * ((Br[r] - Br[r + 1]) * PLeft.DistanceTo(PRight));
}
rbpts = P;
return(parametricError);
}
public void It_Returns_The_KnotSpan_Given_A_Parameter(int expectedValue, double parameter)
{
// Arrange
KnotVector knotVector = new KnotVector {
0, 0, 0, 1, 2, 3, 4, 4, 5, 5, 5
};
int degree = 2;
// Act
int result = knotVector.Span(knotVector.Count - degree - 2, 2, parameter);
// Assert
result.Should().Be(expectedValue);
}
/// <summary>
/// Computes a point on a non-uniform, non-rational b-spline curve.<br/>
/// <em>Corresponds to algorithm 3.1 from The NURBS Book by Piegl and Tiller.</em>
/// </summary>
/// <param name="curve">The curve object.</param>
/// <param name="parameter">Parameter on the curve at which the point is to be evaluated</param>
/// <returns>The evaluated point on the curve.</returns>
internal static Point3 PointAt(NurbsBase curve, double parameter)
{
List <Point4> controlPts = curve.ControlPoints;
KnotVector knots = curve.Knots;
int n = knots.Count - curve.Degree - 2;
int knotSpan = knots.Span(n, curve.Degree, parameter);
List <double> basisValue = BasisFunction(curve.Degree, knots, knotSpan, parameter);
Point4 pointOnCurve = Point4.Zero;
for (int i = 0; i <= curve.Degree; i++)
{
double valToMultiply = basisValue[i];
Point4 pt = controlPts[knotSpan - curve.Degree + i];
pointOnCurve.X += valToMultiply * pt.X;
pointOnCurve.Y += valToMultiply * pt.Y;
pointOnCurve.Z += valToMultiply * pt.Z;
pointOnCurve.W += valToMultiply * pt.W;
}
return(new Point3(pointOnCurve));
}
/// <summary>
/// Splits (divides) the surface into two parts at the specified parameter
/// </summary>
/// <param name="surface">The NURBS surface to split.</param>
/// <param name="parameter">The parameter at which to split the surface, parameter should be between 0 and 1.</param>
/// <param name="direction">Where to split in the U or V direction of the surface.</param>
/// <returns>If the surface is split vertically (U direction) the left side is returned as the first surface and the right side is returned as the second surface.<br/>
/// If the surface is split horizontally (V direction) the bottom side is returned as the first surface and the top side is returned as the second surface.<br/>
/// If the spit direction selected is both, the split computes first a U direction split and on the result a V direction split.</returns>
internal static NurbsSurface[] Split(NurbsSurface surface, double parameter, SplitDirection direction)
{
KnotVector knots = surface.KnotsV;
int degree = surface.DegreeV;
List <List <Point4> > srfCtrlPts = surface.ControlPoints;
if (direction != SplitDirection.V)
{
srfCtrlPts = CollectionHelpers.Transpose2DArray(surface.ControlPoints);
knots = surface.KnotsU;
degree = surface.DegreeU;
}
List <double> knotsToInsert = CollectionHelpers.RepeatData(parameter, degree + 1);
int span = knots.Span(degree, parameter);
List <List <Point4> > surfPtsLeft = new List <List <Point4> >();
List <List <Point4> > surfPtsRight = new List <List <Point4> >();
NurbsBase result = null;
foreach (List <Point4> pts in srfCtrlPts)
{
NurbsCurve tempCurve = new NurbsCurve(degree, knots, pts);
result = KnotVector.Refine(tempCurve, knotsToInsert);
surfPtsLeft.Add(result.ControlPoints.GetRange(0, span + 1));
surfPtsRight.Add(result.ControlPoints.GetRange(span + 1, span + 1));
}
if (result == null)
{
throw new Exception($"Could not split {nameof(surface)}.");
}
KnotVector knotLeft = result.Knots.GetRange(0, span + degree + 2).ToKnot();
KnotVector knotRight = result.Knots.GetRange(span + 1, span + degree + 2).ToKnot();
NurbsSurface[] surfaceResult = Array.Empty <NurbsSurface>();
switch (direction)
{
case SplitDirection.U:
{
surfaceResult = new NurbsSurface[]
{
new NurbsSurface(degree, surface.DegreeV, knotLeft, surface.KnotsV.Copy(), CollectionHelpers.Transpose2DArray(surfPtsLeft)),
new NurbsSurface(degree, surface.DegreeV, knotRight, surface.KnotsV.Copy(), CollectionHelpers.Transpose2DArray(surfPtsRight))
};
break;
}
case SplitDirection.V:
{
surfaceResult = new NurbsSurface[]
{
new NurbsSurface(surface.DegreeU, degree, surface.KnotsU.Copy(), knotLeft, surfPtsLeft),
new NurbsSurface(surface.DegreeU, degree, surface.KnotsU.Copy(), knotRight, surfPtsRight)
};
break;
}
case SplitDirection.Both:
{
NurbsSurface srf1 = new NurbsSurface(degree, surface.DegreeV, knotLeft, surface.KnotsV.Copy(), CollectionHelpers.Transpose2DArray(surfPtsLeft));
NurbsSurface srf2 = new NurbsSurface(degree, surface.DegreeV, knotRight, surface.KnotsV.Copy(), CollectionHelpers.Transpose2DArray(surfPtsRight));
NurbsSurface[] split1 = Split(srf1, parameter, SplitDirection.V);
NurbsSurface[] split2 = Split(srf2, parameter, SplitDirection.V);
surfaceResult = split2.Concat(split1).ToArray();
break;
}
}
return(surfaceResult);
}
/// <summary>
/// Inserts a collection of knots on a curve.<br/>
/// <em>Implementation of Algorithm A5.4 of The NURBS Book by Piegl and Tiller.</em>
/// </summary>
/// <param name="curve">The curve object.</param>
/// <param name="knotsToInsert">The set of knots.</param>
/// <returns>A curve with refined knots.</returns>
internal static NurbsBase KnotRefine(NurbsBase curve, IList <double> knotsToInsert)
{
if (knotsToInsert.Count == 0)
{
return(curve);
}
int degree = curve.Degree;
List <Point4> controlPoints = curve.ControlPoints;
KnotVector knots = curve.Knots;
// Initialize common variables.
int n = controlPoints.Count - 1;
int m = n + degree + 1;
int r = knotsToInsert.Count - 1;
int a = knots.Span(degree, knotsToInsert[0]);
int b = knots.Span(degree, knotsToInsert[r]);
Point4[] controlPointsPost = new Point4[n + r + 2];
double[] knotsPost = new double[m + r + 2];
// New control points.
for (int i = 0; i < a - degree + 1; i++)
{
controlPointsPost[i] = controlPoints[i];
}
for (int i = b - 1; i < n + 1; i++)
{
controlPointsPost[i + r + 1] = controlPoints[i];
}
// New knot vector.
for (int i = 0; i < a + 1; i++)
{
knotsPost[i] = knots[i];
}
for (int i = b + degree; i < m + 1; i++)
{
knotsPost[i + r + 1] = knots[i];
}
// Initialize variables for knot refinement.
int g = b + degree - 1;
int k = b + degree + r;
int j = r;
// Apply knot refinement.
while (j >= 0)
{
while (knotsToInsert[j] <= knots[g] && g > a)
{
controlPointsPost[k - degree - 1] = controlPoints[g - degree - 1];
knotsPost[k] = knots[g];
--k;
--g;
}
controlPointsPost[k - degree - 1] = controlPointsPost[k - degree];
for (int l = 1; l < degree + 1; l++)
{
int ind = k - degree + l;
double alfa = knotsPost[k + l] - knotsToInsert[j];
if (Math.Abs(alfa) < GSharkMath.Epsilon)
{
controlPointsPost[ind - 1] = controlPointsPost[ind];
}
else
{
alfa /= (knotsPost[k + l] - knots[g - degree + l]);
controlPointsPost[ind - 1] = (controlPointsPost[ind - 1] * alfa) +
(controlPointsPost[ind] * (1.0 - alfa));
}
}
knotsPost[k] = knotsToInsert[j];
--k;
--j;
}
return(new NurbsCurve(degree, knotsPost.ToKnot(), controlPointsPost.ToList()));
}
