SOLARSYSTEM, Version 2D
RETURNED
VALUE:
(short int)
0...Everything OK.
1...Invalid value of body or origin.
2...Error detected by JPL software.
Discussion
This version serves as the interface between the Jet Propulsion Laboratory's lunar and planetary
ephemeris software and NOVAS-C. The function contains a single call to JPL's Fortran subroutine pleph,
which in turn calls other Fortran subroutines in the JPL ephemeris software package. The user is
responsible for obtaining the Fortran ephemeris package from JPL, setting up the binary, random-access
ephemeris file, and linking the JPL Fortran with NOVAS-C. See the Implementation Notes below.
The body identification numbers to be used with this version are: Sun,
body=
10; Mercury,
body=
1;
Venus,
body=
2; Earth,
body=
3; Mars,
body=
4; Jupiter,
body=
5; Saturn,
body=
6; Uranus,
body=
7;
Neptune,
body=
8; Pluto,
body=
9; Moon,
body=
11.
Implementation Notes
In order to use NOVAS-C with solarsystem version 2D, you must first obtain the export planetary
ephemeris package from JPL. Be sure to choose an ephemeris whose coordinates are oriented to the mean
equator and equinox of standard epoch J2000.0, such as DE200 or DE403. The export package is
available over the Internet from the anonymous ftp server navigator.jpl.nasa.gov/ephem/export and consists
of several large ASCII data files and software provided in the form of Fortran source code. An installation
guide is also included. The installation process consists of converting the (large) file of ASCII ephemeris
data to binary, direct-access form using a supplied utility program. Then, the binary file is verified using
another utility program and a file of comparison data. If the verification process is successful, the
ephemeris file is ready to use. The ephemeris data is obtained from the binary file by calling the access
subroutines provided in the export package.
Important Note
Over the years, there have been several versions of the JPL export ephemeris software. The following
discussion specifically refers to the software version documented in "The JPL Export Planetary
Ephemeris", 29 June 1990 revision 1, by E. M. Standish and X X Newhall of JPL. Use of solarsystem
version 2D with other versions of the JPL software will require minor modifications to the solarsystem
source code.
Version 2D of solarsystem (in C) obtains ephemeris data from the binary file by calling JPL
subroutine pleph (in Fortran). The C function has a few features that make it possible for it to exchange
data with the Fortran subroutine. First, all of the arguments of the call to pleph in the function are
addresses, since Fortran uses call by address instead of call by value, for arguments of subroutines.
Second, all of the integer arguments in the call are designated as type
long int
in the C function in an
attempt to match the Fortran
INTEGER
default. Finally, the "alternate return" asterisk argument (last item
in the pleph argument list) is designated as a
long int
in the C function; the returned value is used as an
error flag. The
DOUBLE PRECISION
arguments in the subroutine are designated as type
double
in the
C function.
Probably the biggest hurdle in implementing version 2D of solarsystem will involve the proper
compiling and linking of the mixed-language files. The procedures will be specific to your computing
platform; therefore, you will have to consult your compiler manual for detailed instructions. The following
