The routine geom3d[randpoint](w, x, y, z) returns a point with the x-coordinate, y-coordinate, and z-coordinate in the interval specified by x, y, and z respectively.

When the second argument is a line, a plane, or a sphere, geom3d[randpoint] returns a point on that geometric object.

If the object obj is a line, and the third optional argument which is a range is given, w is a point of the line segment such that the parameter in the parametric equation of the line lies in that range.

If the object obj is a sphere, and the optional third, fourth arguments which are ranges are given, w is in general the point with the x-coordinate and y-coordinate restricted inside these ranges.