This routine computes the Jacobian of the transformation from rectangular to latitudinal coordinates.
Variable I/O Description -------- --- -------------------------------------------------- x I X-coordinate of point. y I Y-coordinate of point. z I Z-coordinate of point. jacobi O Matrix of partial derivatives.
x, y, z are the rectangular coordinates of the point at which the Jacobian of the map from rectangular to latitudinal coordinates is desired.
jacobi is the matrix of partial derivatives of the conversion between rectangular and latitudinal coordinates. It has the form .- -. | dr/dx dr/dy dr/dz | | dlon/dx dlon/dy dlon/dz | | dlat/dx dlat/dy dlat/dz | `- -' evaluated at the input values of x, y, and z.
When performing vector calculations with velocities it is usually most convenient to work in rectangular coordinates. However, once the vector manipulations have been performed it is often desirable to convert the rectangular representations into latitudinal coordinates to gain insights about phenomena in this coordinate frame. To transform rectangular velocities to derivatives of coordinates in a latitudinal system, one uses the Jacobian of the transformation between the two systems. Given a state in rectangular coordinates ( x, y, z, dx, dy, dz ) the corresponding latitudinal coordinate derivatives are given by the matrix equation: t | t (dr, dlon, dlat) = jacobi | * (dx, dy, dz) |(x,y,z) This routine computes the matrix | jacobi| |(x, y, z)
Suppose one is given the bodyfixed rectangular state of an object ( x(t), y(t), z(t), dx(t), dy(t), dz(t) ) as a function of time t. To find the derivatives of the coordinates of the object in bodyfixed latitudinal coordinates, one simply multiplies the Jacobian of the transformation from rectangular to latitudinal coordinates (evaluated at x(t), y(t), z(t) ) by the rectangular velocity vector of the object at time t. In code this looks like: #include "SpiceUsr.h" . . . /. Load the rectangular velocity vector vector recv. ./ recv = dx ( t ); recv = dy ( t ); recv = dz ( t ); /. Determine the Jacobian of the transformation from rectangular to latitudinal coordinates at the rectangular coordinates at time t. ./ dlatdr_c ( x(t), y(t), z(t), jacobi ); /. Multiply the Jacobian on the right by the rectangular velocity to obtain the latitudinal coordinate derivatives latv. ./ mxv_c ( jacobi, recv, latv );
1) If the input point is on the z-axis (x and y = 0), the Jacobian is undefined. The error SPICE(POINTONZAXIS) will be signaled.
W.L. Taber (JPL) N.J. Bachman (JPL)
-CSPICE Version 1.0.0, 13-JUL-2001 (WLT) (NJB)
Jacobian of rectangular w.r.t. latitudinal coordinates