Translations:B-Splines/34/en

From the videos we can collect useful "rules" for B-splines:
 * The first and last control point is the end/start point of the spline.
 * Like for Bézier curves, splines always begin tangentially to the line between the startpoint and the first control point (and end tangentially to the line between the last control point and the endpoint).
 * A union of $$S$$ Bézier curves with the degree $$D$$ has $$S+D$$ control points.
 * Since one is in most cases working with cubic B-splines we can then state that $$N$$ control points lead to $$N-3$$ Bézier segments and in turn $$N-4$$ segment junction points.
 * A B-spline with the degree $$D$$ offers at every point a continuous $$D-1$$ order derivative.
 * For a cubic B-spline this means that the curvature (second order derivative) does not change when traveling from one segment to the next one. This is a very useful feature as we will later see.