fitorbit(1) --- Imcat Users Guide --- section: imcattools_orbits --- last changed: Sun Apr 13 HST
fitorbit - find least squares orbit solutionSYNOPSIS
fitorbit initsolcat np [-tcl dtmax]DESCRIPTION
fitorbit finds a minimum chi-squared solution for a set of observations given an initial solution.
fitorbit first reads an lc format catalog initsolcat containing the a preliminary solution ra0[3], va0[3], as well as the position re0[3] and velocity ve0[3] of the Earth at t0 the initial time t0 (though these just get passed through. It also contains the number of observations nt. It then reads a set of nt observations re[3], rho[3], nobs[3], sigma and t from obscat, and finds a minimum chi^2 by propagating from the t0 solution and computing the residuals. By default it uses Kepler elements but with -tcl flag will use time-centered leapfrog with maximum timestep dtmax. Minimum is found using Powell's method. Here re[] is the geocenter, rho[] is the position of the observatory realtive to the geocenter and nobs is a unit vector in the direction ra[] - re[]. fitorbit outputs a series of np+2 sets of phase-space coordinates r[], v[] where the first set is the observer, the second is the asteroid solution and subsequent np sets of coordinates are solutions obtained by randomly perturbing the observations with Gaussian distributed errors with rms value sigma. Also output is the minimum value of chi-squared for the solution, and a particle number p (-1 for the observer, 0 for the actual solution and 1 ... np for the virtual asteroids. SEE ALSOmakeobs_inertial(1), makeobs_circ(1), laplace3(1), tcl_evolve(1), r2n(1), tcl_evolveN(1), orbs2obs(1).
AUTHOR
Nick Kaiser --- kaiser@hawaii.edu