Merge branch 'gracedb-reading-example' into 'master'

Add GraceDB reading example

See merge request lscsoft/bilby!334

examples/open_data_examples/read_gracedb_data.py

+#!/usr/bin/env python
+"""
+Tutorial to demonstrates reading and plotting the GraceDB data for GW170608,
+the lightest GWTC-1 BBH event.
+
+This tutorial must be run on a LIGO cluster.
+"""
+
+import bilby
+
+label = 'GW170608'
+outdir = label + '_out'
+# List of detectors involved in the event. GW170608 is pre-August 2017 so only
+# H1 and L1 were involved
+detectors = ['H1', 'L1']
+# Names of the channels and query types to use, and the event GraceDB ID - ref.
+# https://ldas-jobs.ligo.caltech.edu/~eve.chase/monitor/online_pe/C02_clean/
+# C02_HL_Pv2/lalinferencenest/IMRPhenomPv2pseudoFourPN/config.ini
+channel_names = ['H1:DCH-CLEAN_STRAIN_C02', 'L1:DCH-CLEAN_STRAIN_C02']
+query_types = ['H1_CLEANED_HOFT_C02', 'L1_CLEANED_HOFT_C02']
+gracedb = 'G288686'
+# Calibration number to inform bilby's guess of query type if those provided are
+# not recognised
+calibration = 2
+# Duration of data around the event to use
+duration = 16
+# Duration of PSD data
+psd_duration = 1024
+# Time of event, stored in bilby
+trigger_time = bilby.gw.utils.get_event_time(label)
+# Minimum frequency and reference frequency
+minimum_frequency = 10  # Hz
+
+# Get frame caches
+candidate, frame_caches = bilby.gw.utils.get_gracedb(
+    gracedb, outdir, duration, calibration, detectors, query_types)
+
+# Set up interferometer objects from the cache files
+interferometers = bilby.gw.detector.InterferometerList([])
+
+for cache_file, channel_name in zip(frame_caches, channel_names):
+    interferometer = bilby.gw.detector.load_data_from_cache_file(
+        cache_file, trigger_time, duration, psd_duration, channel_name)
+    interferometer.minimum_frequency = minimum_frequency
+    interferometers.append(interferometer)
+
+# Plot the strain data
+interferometers.plot_data(outdir=outdir, label=label)