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snapfits - convert a snapshot file to a fits file.
snapfits in=snapshot
out=fitsfile [parameter=value]
snapfits converts a snapshot
to a fits file, in the random groups format (See: xxx). See the section
on ’FITS KEYWORDS’ below for a more detailed description. The kind of parameters
written can be choosen with the options keyword (see below). The default
is 7 (masses, positions and velocities for a 3-dimensional simulation).
Note: Only one snapshot can be written. The time of the snapshot is not
saved yet.
The following parameters are the ones whose meaning
is different from the one in snapplot:
- in=in-file
- input file, must be in
snapshot(5NEMO)
format [no default].
- out=out-file
- output file, will be in
fits(5NEMO)
format [no default].
- options=opt1[,opt2...]
- List of options, separated
by comma’s (no spaces), of the items to be saved in the output FITS file.
They can be any combination of: mass, phase (pos, vel), phi and acc. Note
that the order of items written is fixed, as described above. Even for options=pos,mass
the mass will be preceded by the 2/3 positions of the particle. [default:
mass,phase].
- comment=comment
- One comment line with up to about [70] characters
can be used to identify this FITS file. [default: empty].
The
data is written using the random groups format in FITS without any primary
data matrix. Hence NAXIS1=0, PGROUP the number of items per particle to
be output (7 being the default), and GCOUNT the total number of bodies
in a snapshot. The external format of the data is IEEE floating point (BITPIX
= -32 or -64, depending on precision required). There will be no scaling (default
PZEROnnn and PSCALnnn), whereas the axes are labeled using the PTYPEnnn
keyword. They can be any of MASS, POSn, VELn, PHI and ACCn (n=1,..NDIM).
There
is really no use for this program, since the general way to transport data
is using the general ascii format (see atos(1NEMO)
or snapprint(1NEMO)
)
or ascii structured files (see tsf(1NEMO)
). For large amounts of datafiles
this fits format may actually become useful. It was merely created for the
authors amusement and to show how the FITS format could be used to export
N-body data.
There is no program fitssnap yet. As the need arises, and this
fits-i/o format becomes popular, the author may be poked to create one.
atos(1NEMO)
, stoa(1NEMO)
, tsf(1NEMO)
, rsf(1NEMO)
, snapprint(1NEMO)
Peter Teuben
src/pjt/image snapfits.c, snapfits.1
19-mar-90 V1.0: Created PJT
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