SPLAT-VO can read and write spectra stored in a wide variety of formats, either stored as 1D spectra or as columns in tables. 1D spectral formats supported are Starlink NDF & NDX, FITS and simple TEXT files. Table formats supported are FITS (binary and ascii), VOTable and more complex TEXT files. The 1D data formats currently have the best coordinate system support, so are recommended when a choice can be made. Some support is available for 2 and 3D data, see later).
Normally SPLAT-VO differentiates these types using a preset list of file extensions, for instance NDFs
can only be stored in container files that have the extension
.sdf, FITS files usually have one of the
.fit and TEXT files
.lis and NDX format spectra, when stored on disk,
will have extension
.xml. However, you can choose a specific format when opening a file using the
File->Open dialogue, so you can ask that a TEXT file is opened as a table, this allows you to select the
columns. There is also a special type known as
guess. When you choose that attempts to
open the spectrum as different types are made until one succeeds, or the possibilities are
You can specify a type for all the spectra opened on the command-line using the --type argument. Valid values for --type are:
You free to truncate these values as long as they remain unique (so --type line will work for line identifiers).
Currently line identifier catalogues represent a special case and currently may have a single format -
TEXT based in files with extension
1D spectra stored in TEXT files must have the format of one, two or three columns of data, separated by whitespace (that is spaces or tabs). Any comments in the file must be indicated by a hash sign, blank lines are also allowed. The three columns should have the following values:
The wavelength and error columns being optional (if you don’t have a wavelength column a simple row index is used, note you cannot have errors without wavelengths) . If you choose to open a TEXT file as a table you can select which columns should be used for these values, and the following rules apply:
The format of line identification catalogues is like that of simple TEXT spectral files, except the second
column contains a string that identifies the line (with no spaces, i.e.
H alpha). It is also
possible to define the system of the coordinate values in a header section, see the SPLAT-VO built-in
catalogues for examples of this.
NDFs stored within container files can be accessed, but only by entering the full HDS path on the command-line or in the File->Open dialogue. FITS extensions may also be open in this fashion (by appending the extension number in square brackets).
An alternative to specifying the component information is to use the component browser window
, to see the contents of FITS and NDF files and choose the component to display directly. This uses the
same techniques as the special
Internally all these formats are stored as double precision coordinates and data values. SPLAT-VO only requires that coordinates increase or decrease monotonically when performing any analyses.
If you have images or cubes that contain data that you want to view as spectra in some fashion, then SPLAT-VO will attempt to do this for you. There are three fundamental modes for doing this:
spectrumor the planes of a cube into a set of
spectraby adding together all values that lie perpendicular to the dispersion axis (so the spectra run along this axis, what a good spectral displaying tool should do).
The default is to collapse. When collapsing cubes you have the option of which axis to step along
selecting image planes, this is known as the
select axis. To determine which option is used to
handle your cubes or images you can either set values on the command-line, along with
your spectra, or choose options in the open file dialogue. A command line that uses axis
3 as the dispersion axis and steps along axis 2 when choosing image planes might look
or in shorthand:
If you don’t choose a dispersion axis SPLAT-VO will make a good intelligent guess about this and
step along the first axis that isn’t the dispersion axis. The other possible values for
vectorize. These are described as
extract all spectra and
open whole as 1D,
respectively, in the open file dialogue.