Projection Commands

 

    The Projection commands are not standalone commands: they can only be operative within the context of command files and pipelines, i.e. they must be thought of in relation to other Projection commands which have been executed within the same task.

There are only four kinds of Projection commands: the INPUT, the OUTPUT, the SELECT and the BIN commands. The COUNT command is just a variation of the SELECT command, in the sense that the SELECT commands create virtual lists of selected photons, while the COUNT commands are just counting the photons which are selected. The syntax of the COUNT and SELECT commands is otherwise identical.

The general structure of a Projection command may be outlined as in the following:

<identifier> <command> <reference :> <label_list> <parameter_list>

The command is one of the Projection commands listed in Table 4.2.

The label list is a list of one or more strings, separated by commas, among the ones listed in Table 4.3. Each label corresponds to a photon parameter.

  
Table 4.3: Photon parameter labels and their meaning

 

The label list is bound to different restrictions, according to the specific command requirements. Here some examples of label lists in Projection command lines are given:

       select      TIME             10000,20000
       bin/image   XDET,YDET        #512,#512
       bin         AMPL             1
       output      TIME,XPIX,YPIX   to photon_list_a

   

The reference is a character string used in making reference to Projection commands which have been previously executed within the same task. When not indicated the reference is automatically meant to the last executed Projection command. When indicated, it must be separated by a colon (:) from the label list. Here some examples of Projection commands containing also arbitrary reference strings are given:

       select      ABC       :TIME      10000,20000
       bin/image   DEFGH(1+2):XDET,YDET #512,#512
       bin         MYDAT(2,5):AMPL      1
       output      RATES     :       to photon_list_a

       

The identifier is an optional character string up to 6 characters long, used to label a Projection command line. The identifier string is used in the reference mechanism between different Projection commands, and its function will be clarified in the context of Projection command files and pipelines (sections 4.3.2 and 4.3.3). The identifier string can be inserted at the beginning of command lines in a Projection command file, or more generally -- preceded by the keyword ID -- at the command line end. Here are some examples of Projection command lines having the same identifier string ABC:

ABC = select time 10000,20000
      bin/image xdet,ydet #512,#512  ID = ABC
      bin ampl 1    ID=ABC

     

Finally, the parameter list is either a sequence of numerical parameters or filenames separated by blanks or commas or logical symbols according to the command requirements. Here some examples of parameter lists are given: their meaning should be apparent to the reader.

       input                 events
       select time           > 10000
       select amplitude      7 to 246
       select raw_ampl       18
       bin/image             #512, #512
       select/ring xdet,ydet (100,200) radius = 500
       bin time              10
       output to             image1,image2,image3

                       

  
Table 4.4: Projection commands -- Curly brackets indicate optional entries

             

Specifically for BIN and SELECT commands, the command line structure may be extended as follows:

<ident> <command> < ref : > <label> <[par_list1] [par_list2] [par_list3] ...>

The definition of multiple parameter lists delimited by squared brackets allows the production of several virtual datasets in parallel. When n parameter lists are defined for the same Projection command, the input virtual dataset is processed n times according to the different sets of parameters. The output of the command line consists of n independent virtual datasets. If an identifier string was specified, the output datasets are labeled by the identifier string itself followed by an index enclosed in round brackets (see section 4.3.2).

In the following command line it is shown how to select photons from different circles in the sky, keeping the resulting lists separate:

SELECT/RING [center=(0,0) radius=500]  [center=(100,100) rad=400]

With the following command, three light curves with binsizes 1, 10 and 100 are derived simultaneously from the same input photon list:

BIN TIME  [1] [10] [100]

             

The applications of this powerful element of syntax will be clear after reading sections 4.3.2 and 4.3.3.

A minimal syntax for the Projection commands can be found in Table 4.4. At this section end, a complete overview of the Projection command syntax is given in a flow-chart fashion.

A more detailed description of the Projection command syntax is given in the following:

 
• INPUT
• SELECT
• BIN
• OUTPUT