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