Channel Selection Syntax

MSSelection module is currently used to only parse the channel selection expression to produce the START,STOP,STEP tuples. No channel based selection is actually applied to the data. The list of tuples per SPW is passed to the application program layer and the interpretation of the tuples for actual selection depends on the application programmer.

Channel specification (referred to as CHANSPEC in the following description) is a START,STOP,STEP tuple corresponding to the first frequency channel, the last frequency channel and the step size to increment from the first to the last channel. The START and STOP part of the tuple can be range specification for the range [START, STOP] followed by an optional STEP size.

START and STOP part of the tuple can be specified as a single integer or physical quantity or as a range of integers or physical quantities. A single integer is treated as a channel index and the tuple corresponds to [ID,ID,1]. A single physical quantity is matched with the exact frequency value of the channels and tuple of matched channel index is constructed as [ID,ID,1]. A range of integers given as N0$\sim$N1 is used to construct a tuple [N0,N1,1]. Similarly for a range of physical quantities.

If a START,STOP part of the tuple specification is followed by "^STEP", the STEP is used as the third value of the tuple. STEP specification is a single integer or physical quantity. E.g. 0$\sim$10^2 is converted to a START,STOP,STEP tuple [0,10,2].

A channel selection expression is a semi-colon separated list of channel specifications. E.g.

• chan=1;2;3 selects channels 1,2 and 3.
• chan=1$\sim$3 selects channels 1,2 and 3.
• chan=0$\sim$10^2 selects channels in the range [0,10] with a step size of 2
• chan=1421MHz selects a frequency channel corresponding to the frequency 1421.0 MHz
• chan=1421$\sim$1500MHz selects all channels in the range [1412.0, 1500.0] MHz
• chan=1421$\sim$1500MHz^10KHz selects all channels in the range [1421.0, 1500.0] MHz in steps of 10 KHz.
• chan=1421$\sim$1500MHz^10KHz ; 0$\sim$10^2 ; 20 ; 30; 40 selects all channels in the range [1421.0, 1500.0] MHz in steps of 10KHz, all channels with indexes in the range [0,10] in steps of 2 channels and channels 10, 20 and 30.