The order of derivatives

• = 0 , only the position is computed. The first three numbers of PVAJ are valid for the results.
• = 1 , only the position and velocity are computed. The first six numbers of PVAJ are valid for the results.
• = 2 , only the position, velocity and acceleration are computed. The first nine numbers of PVAJ are valid for the results.
• = 3 , the position, velocity and acceleration and jerk are computed. The first twelve numbers of PVAJ are valid for the results.

If order equals to 1, the behavior of calceph_compute_order() is the same as calceph_compute_unit().