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JPLEPHMAKE

JPLEPHMAKE

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 $



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