;+
; NAME:
;   JPLEPHMAKE
;
; AUTHOR:
;   Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
;   craigm@lheamail.gsfc.nasa.gov
;   UPDATED VERSIONs can be found on my WEB PAGE: 
;      http://cow.physics.wisc.edu/~craigm/idl/idl.html
;
; PURPOSE:
;   Make a new ephemeris suitable for interpolation by JPLEPHINTERP
;
; MAJOR TOPICS:
;   Planetary Orbits, Interpolation
;
; CALLING SEQUENCE:
;   JPLEPHREAD, INFO, RAW, OBJ, T, CX, CY, CZ, $
;               [ POSUNITS=, AUTHOR=, DATE=, OBJECTNAME=, ]
;               [ KEYWORDS=, KEYVALUES=, /RESET ]
;
; DESCRIPTION:
;
;   JPLEPHMAKE is a utility routine which forms an ephemeris table
;   suitable for interpolation with JPLEPHINTERP.  This is a way for
;   users to make or augment an ephemeris of solar system bodies not
;   already present in the JPL planetary ephemeris.  This routine only
;   creates new ephemerides in memory.  No facility is provided to
;   write to disk.
;
;   The user must have already estimated the Chebyshev polynomial
;   coefficients for the body of interest.  One way to do this is with
;   CHEBGRID from the Markwardt library.  
;
;   The two options are either to create a new ephemeris or to augment
;   an existing one.  Augmentation merely means that new columns are
;   added to an existing ephemeris table.  The JPL ephemeris itself
;   can be augmented.
;
;   Even when creating a new ephemeris from scratch, passing an
;   existing INFO structure based on another epehemeris is strongly
;   recommended, because the structure usually contains planetary
;   masses, physical constants, etc. which are relevant.
;
;
;
; PARAMETERS: 
;
;
;   INFO - upon input, an existing INFO structure based on a known
;          ephemeris.  Upon output, a modified INFO structure.
;
;          If INFO is undefined upon input, or the RESET keyword is
;          set, then the returned INFO is set to a generic header.
;
;   RAW - upon input, an existing set of Chebyshev coefficients.  Upon
;         output, the new or augmented set of coefficients.
;
;         If RAW is undefined upon input, or if the RESET keyword is
;         set, then the returned RAW variable is initialized to a new
;         set of keywords.
;
;   OBJ - scalar string, name of the object.
;
;   T - array of times, in Julian Days (TDB), which refer to the
;       *start* epoch of each granule.  [ In the terminology of the
;       JPL ephemeris and CHEBGRID, a "granule" is a single
;       subinterval over which a Chebyshev polynomial is fitted. ] If
;       an existing ephemeris is to be augmented, then T must overlap
;       exactly.
;
;   CX, CY, CZ - arrays of Chebyshev polynomial coefficients.
;
;
;
; KEYWORD PARAMETERS:
;
;   POSUNITS - a scalar string, the units of position as fitted by CX,
;              CY, and CZ.  Allowed values:
;                 'KM' - kilometers  (default)
;                 'CM' - centimeters
;                 'AU' - astronomical units
;                 'LT-S' - light seconds
;
;   NSUBINTERVALS - Number of granules per time sample.
;                   Default: 1
;
;   RESET - if set, then a new ephemeris table is created.  Any
;           Chebyshev coefficients in RAW are overwritten.
;
;   AUTHOR - a scalar string, an identifier giving the author of the
;            new ephemeris.
;            Default: ''
;
;   DATE - a scalar string, the creation date of the ephemeris.
;          Default: SYSTIME(0)
;
;   KEYWORDS - an optional string array, giving any header keywords to
;              be added to the ephemeris (in conjunction with
;              KEYVALUES).
;              Default: (none)
;
;   KEYVALUES - an optional double array, giving any header values for
;               the keywords specified by KEYWORDS.
;
;               Default: (none)
;
;
; EXAMPLE:
;
;
; REFERENCES:
;
;   JPL Export Ephmeris FTP Site
;      ftp://navigator.jpl.nasa.gov/pub/ephem/export/
;      (ephemeris files are available here, however, they must be
;      converted to FITS format using the "bin2eph" utility found in
;      AXBARY)
;
;
; SEE ALSO
;   JPLEPHREAD, JPLEPHINTERP, JPLEPHTEST
;   
; MODIFICATION HISTORY:
;   Written and Documented, CM, Mar 2002
;   Corrected way that ephemerides are merged, also
;     way that AUTHOR field is filled, 29 May 2002, CM
;
;  $Id: jplephmake.pro,v 1.4 2002/05/29 20:07:41 craigm Exp $
;
;-
; Copyright (C) 2002, Craig Markwardt
; This software is provided as is without any warranty whatsoever.
; Permission to use, copy and distribute unmodified copies for
; non-commercial purposes, and to modify and use for personal or
; internal use, is granted.  All other rights are reserved.
;-