Data Retrieval

Data retrieval is possible only from the HTML-format output document. Spectra may be retrieved individually or in groups, Spectra are delivered as ASCII files, and are easily imported into standard image processing packages such as IDL, IRAF or MIDAS.

Single spectrum retrieval

To fetch a single spectrum, click on the link in the output table Fetch column corresponding to that spectrum. Single spectra are retrieved uncompressed and, depending on the characteristics of your browser, you will be prompted to give the local filename either before or after download. It is recommended that you use the same naming convention as that under which the data are stored on the servers.

The sizes of the data products are:

Multiple spectrum retrieval

Spectrum selection

You may include/exclude all files of a particular type for multiple retrieval, e.g. Mark:Average, will mark/unmark all spectra of the average photospheric profiles, and to fine-tune your selection further you may include/exclude individual spectra by checking/unchecking them in the Mark column corresponding to their location.

Retrieval format

Multiple spectrum retrieval generates a packed file in either tar or ZIP format. Compression of packed files is recommended for network efficiency, in particular when downloading large data sets. ZIP files are compressed automatically, and for tar files, three compression schemes are available: bzip2, gzip, and compress. Ensure that the corresponding unpacking and decompression programs are available on your system before selecting the retrieval scheme from the pull-down menu (default tar.gz).

The following tables may be useful for helping you decide on which packing and compression scheme to use.
Scheme Size in Mbytes
bzip2 1.66 514
gzip 1.88 656
ZIP 1.93 656
compress2.40 687
tar 10 2290
The most efficient compression is achieved by bzip2, but you should be aware that its compression/decompression cycle is more than ~5 times longer than for the other schemes. Retrieval of the selected spectra is effected by clicking the corresponding Retrieve Marked Data button. You will be prompted to assign local filenames for the packed, compressed files from each server either before or after download, depending on the browser you use. Ensure that you choose different filenames for the downloads from each server; it is recommended that you name them according to the standard naming convention for the packing and compression scheme chosen (that is, file.tar.gz, file.tar.bz2, file.tar.Z, file.tar or file.zip).

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Last update: May 2014.