The channel command gives easy access to individual channels of a spectrum. This command provides access to the contents of an entire spectrum. The initial use case for this was to provide spectra to clients of the SpecTcl REST plugin. Clearly another use caser would be to provide a mechanism to export spectra in file formats not supported by SpecTcl's swrite command.
The -json selects a result that is in
JavaScript Object Notation (JSON). If that's omitted a Tcl
friendly representation is used. Note that metadata about the
spectrum (the spectrum definition) is not returned. You would
have to couple this command with the appropriate
spectrm -list command to get that.
Depending on the use of the -json option, the
command produces data either in a Tcl friendly way or as a
JavaScript Object Notation (JSON) object.
Output is zero suppressed. It consists of a list of lists. Each list element contains the coordinates of a non-zero channel followed by the value at that channel.
For 1-d spectra each nonzero channel is represented by a two element list. The list contains the channel number followed by the channel value.
For 2-d spectra the output is similar. Each channel is represented by a three element list. The list contains the x and y channel number that define a channel in the 2-d spectrum followed by the value at that channel. Again, only non-zero channels will appear in the output list.
JSON output format is web friendly. REST interfaces (including
the SpecTcl REST plugin), often return responses as JSON
objects. The output from scontents -json,
is a JSON array.
Each array element represents a non-zero channel. For 1-d spectra, each element of the array is an object that contains the attributes:
The channel number of a non zero channel in the spectrum.
The value of that channel.
For 2-d spectra again, the result is an array of objects. In addition to the attributes described for 1-d output, a channel object has a y object, the y coordinate of the non-zero channel.