Two connected Bezier patches are two (cubic) Bezier curves which share one end point. So, we have three "knots" (points) A, B, C placed somewhere in space. A is the start point, B is the end point of the first Bezier curve and the start point of the second Bezier curve. C is the end point of the spline. Each knot has one "control point" ("CP") aa, bb, cc placed somewhere in space. The CP defines the direction and shape of the curve. The connection (knot B) is tangent continuous to create a smooth transition between the patches. Therefore, the middle CPs are always symmetrical relative to knot B. The user adjusts CP "bb" to define both CPs and the shape of the curve in the region of knot B. To plot the curve, the code calculates the curve coordinates from knot A to B and then from knot B to C. The calculation is based on 7 parameters, that is 7 sets of (xyz) space coordinates along the entire curve, starting with "a_parm" for the first knot, ending with "g_parm" for the third knot as shown in the picture. I tried to avoid angles as far as possible, because the angle/coordinates conversion requires complicated calculations. Hence, the user sets the (xyz) coordinates to define the curve parameters and the shape of the path.