Instructions
This service facilitates downloading to and accessing on the user's host a
subset of SPICE kernels from the specified SPICE PDS archive covering
the specified time interval. It uses the kernel coverage information from
the PDS3 index file or PDS4 labels and meta-kernels
(also known as ``furnsh'' kernels)
from the archive to generate one or more ``subset'' meta-kernels
listing only kernels with coverage intersecting the specified time
interval. This service also generates a text file containing the
URLs of the kernels listed in
the ``subset'' meta-kernels, to allow a bulk download of these kernels
to the user's host using the ``wget'' utility.
Follow these steps to use this service:
- Specify start and/or stop times in any format acceptable as input to
SPICE routine STR2ET (see examples)
and click ``Subset'';
- When prompted, save the ``[volume_id_yymmdd_yymmdd].zip'' file to a directory
under which you want to store the data; (Note: some browsers may
save the file to a default location automatically.)
- Unzip ``[volume_id_yymmdd_yymmdd].zip''; (Note: some browsers may unzip
the file at the default location automatically.)
- Depending on your environment, run ``wget_[volume_id_yymmdd_yymmdd].tcsh'' (on UNIX hosts)
or ``wget_[volume_id_yymmdd_yymmdd].bat'' (on Windows hosts) to download kernels using
``wget''; the kernels will be downloaded to a subdirectory named with the
archived PDS3 volume ID (e.g. ``clsp_1000'') or PDS4 bundle ID
(e.g. ``maven_spice'') and will be arranged in the same way
as in the complete archive; (Note: these scripts assume that
``wget'' is installed on your computer and is accessible via the
executable path.)
- Edit the ``subset'' meta-kernel(s) (``*.tm'') to point to the actual
location of the kernels on your computer; if you use a Windows
computer you may also need to change line terminators and ``slashes''
as described in the comments provided in the meta-kernel(s);
- Load the updated ``subset'' meta-kernel(s) to your SPICE-based
application to access the data.
Notes and Limitations
Please note the following when using this service:
- If your specified interval does not intersect the coverage of
binary kernels (SPKs, CKs, etc) included in the complete data archive,
this service will generate ``subset'' meta-kernels and a URL list file
consisting only text kernels because text kernels are considered to be
applicable at all times. Obviously such subsets will have marginal or
zero usability.
- As in the case for any set of kernels, it is not guaranteed that
your subset will provide sufficient data to compute quantities
of interest during the specified period due to coverage gaps and/or
un-availability of data for an object or a frame of interest.
- The subset may include kernels that are not needed to compute
quantities of interest to you.
- The ``wget'' options in the scripts provided to
download kernels are set to ``mirroring', meaning that if a subset
is downloaded to the location of a previously downloaded subset, the
kernels already present on the user's host will not be downloaded
again, reducing the transfer time.