InstructionsThis 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 LimitationsPlease 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.