===== Primitive: Cubic B-spline object [Schmitt et al. 2000] =====

**Definition**: Object defined by F>=0, where F is a B-spline function of three variables
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<m>F(u,v,w) = sum{i=0}{l}{}sum{j=0}{n}{}sum{k=0}{m}{}N_i(u)N_j(v)N_k(w)P_{ijk}</m>\\
<m>P_{ijk}</m> - Control points of the cubic B-spline volume. Only the fourth coordinnate is used\\
<m>N_i(u)</m> : Cubic BSpline blending function.

**Call**: hfCubicBSplineF(x,l,m,n,bbox,ctr_pts);

**Parameters**:

x - point coordinates

l,m,n - number of control points on each axis

bbox - array defining the bounding box of the object

ctr_pts - array of values for each control point

**Test file**: [[http://hyperfun.org/bsplinef.hf|bsplinef.hf]]