Why aren’t my Curves calculating or why do they have terrible shape?

The position of the camera during photography of the curve is key. Think of each section of the curve and imagine it is a straight line on the 3D object. The ideal camera positions for this section of curve, are rotated about this line. Imagine camera station one has a line perpendicularly connecting the camera and the curve line. Now rotate that curve line along its axis by 90 degrees (the line will look the same but the “attached” camera will ‘roll’ 90 degrees about the line still facing the curve. These are the ideal photos for this section. If the curve is not complex these two photos may suffice. But if the curve is circular or changes direction a lot then additional photos will be needed to make that section of curve compute well.