Selecting event data
What you will learn
You will learn how to use the :ref:`ctselect` tool to select relevant events from the simulated event data.
As next step you may want to select some events from the simulated event data. You may want to restrict the events to a region of interest (ROI) of 3 degrees around the pointing direction, you may want to extract a 30 minutes time slice from the data, and you may want to limit the energy range of the events to 0.1 - 100 TeV. You do this event selection using the :ref:`ctselect` tool as follows:
$ ctselect
Input event list or observation definition XML file [events.fits]
Radius of ROI around pointing or specified RA/DEC (0-180) [3.0]
Start time (UTC string, JD, MJD or MET in seconds) [NONE] 2020-01-01T00:10:00
Stop time (UTC string, JD, MJD or MET in seconds) [NONE] 2020-01-01T00:40:00
Lower energy limit (TeV) [0.1]
Upper energy limit (TeV) [100.0]
Output event list or observation definition XML file [selected_events.fits]
This created a new event list FITS file selected_events.fits that contains the selected data. Below an excerpt of the ctselect.log log file that illustrates the event selection:
2018-01-24T14:07:07: +===================+
2018-01-24T14:07:07: | Input observation |
2018-01-24T14:07:07: +===================+
2018-01-24T14:07:07: === GObservations ===
2018-01-24T14:07:07: Number of observations ....: 1
2018-01-24T14:07:07: Number of models ..........: 0
2018-01-24T14:07:07: Number of observed events .: 202210
2018-01-24T14:07:07: Number of predicted events : 0
2018-01-24T14:07:07:
2018-01-24T14:07:07: +=================+
2018-01-24T14:07:07: | Event selection |
2018-01-24T14:07:07: +=================+
2018-01-24T14:07:07: === CTA observation (id=000001) ===
2018-01-24T14:07:07: Input filename ............: events.fits
2018-01-24T14:07:07: Event extension name ......: EVENTS
2018-01-24T14:07:07: GTI extension name ........: GTI
2018-01-24T14:07:07: === Event selection ===
2018-01-24T14:07:07: Time range (MJD) ..........: 58849.0077451852 - 58849.0285785185 days
2018-01-24T14:07:07: Time range (UTC) ..........: 2020-01-01T00:10:00 - 2020-01-01T00:40:00
2018-01-24T14:07:07: Time range (MET) ..........: 631109469.184 - 631111269.184 seconds
2018-01-24T14:07:07: Selected energy range .....: 0.1 - 100 TeV
2018-01-24T14:07:07: Requested RoI .............: Centre(RA,DEC)=(83.63, 22.51) deg, Radius=3 deg
2018-01-24T14:07:07: RoI of data ...............: Centre(RA,DEC)=(83.63, 22.51) deg, Radius=5 deg
2018-01-24T14:07:07: Selected RoI ..............: Centre(RA,DEC)=(83.63, 22.51) deg, Radius=3 deg
2018-01-24T14:07:07: cfitsio selection .........: TIME >= 631109469.18399978 && TIME <= 631111269.18400002 && ENERGY >= 0.10000000 && ENERGY <= 100.00000000 && ANGSEP(83.630000,22.510000,RA,DEC) <= 3.000000
2018-01-24T14:07:07: FITS filename .............: /var/tmp/tmp.0.aFKvXb[EVENTS][TIME >= 631109469.18399978 && TIME <= 631111269.18400002 && ENERGY >= 0.10000000 && ENERGY <= 100.00000000 && ANGSEP(83.630000,22.510000,RA,DEC) <= 3.000000]
2018-01-24T14:07:07:
2018-01-24T14:07:07: +====================+
2018-01-24T14:07:07: | Output observation |
2018-01-24T14:07:07: +====================+
2018-01-24T14:07:07: === GObservations ===
2018-01-24T14:07:07: Number of observations ....: 1
2018-01-24T14:07:07: Number of models ..........: 0
2018-01-24T14:07:07: Number of observed events .: 21974
2018-01-24T14:07:07: Number of predicted events : 0
From the 202210 events in the input event list 21974 events were selected.
Note
Event selection by :ref:`ctselect` in a given dimension can be avoided by specifying NONE (or INDEF, UNDEF or UNDEFINED) for one of the selection parameters. This is recommended rather than specifying the same selection previosuly applied to the data. The following run for example only performs a selection by time but no selection by ROI or energy:
$ ctselect
Input event list or observation definition XML file [events.fits]
Radius of ROI around pointing or specified RA/DEC (degrees) (0-180.) [3.] NONE
Start time (UTC string, JD, MJD or time in seconds) [2020-01-01T00:10:00]
Stop time (UTC string, JD, MJD or time in seconds) [2020-01-01T00:40:00]
Lower energy limit (TeV) [0.1] NONE
Output event list or observation definition XML file [selected_events.fits]