add script to write comCamSim filter files

use galsim.Bandpass to truncate and thin filter curves

python/lsst/obs/lsst/script/write_comCamSim_filter_files.py

@@ -0,0 +1,89 @@
+# This file is part of obs_lsst.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (https://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+import os
+import re
+import numpy as np
+
+import astropy.units as u
+from astropy.table import QTable
+import dateutil.parser
+import galsim
+
+import lsst.utils
+from lsst.meas.algorithms.simple_curve import DetectorCurve
+
+# Write transmission_filter files for the g, r, i band used
+# by LSSTComCamSim.  These are the baseline/filter_[gri].dat
+# files in the throughputs package.
+throughputs_dir = lsst.utils.getPackageDir("throughputs")
+filter_files = [
+    os.path.join(throughputs_dir, "baseline", _)
+    for _ in ("filter_g.dat", "filter_r.dat", "filter_i.dat")
+]
+physical_filters = ("g_01", "r_03", "i_06")
+
+for physical_filter, filter_file in zip(physical_filters, filter_files):
+    throughput = np.genfromtxt(filter_file).transpose()
+    # Use a GalSim.Bandpass object to truncate the curves at low
+    # relative throughput and thin the number of wavelength points.
+    bp = galsim.Bandpass(
+        galsim.LookupTable(*throughput, interpolant="linear"), wave_type="nm"
+    )
+    bp = bp.truncate(relative_throughput=1e-4)
+    bp = bp.thin()
+
+    # Package as a DetectorCurve object.
+    optics_table = QTable(
+        {
+            "wavelength": bp.wave_list * u.nanometer,
+            "efficiency": bp(bp.wave_list) * 100.0 * u.percent,
+        }
+    )
+    curve = DetectorCurve.fromTable(optics_table)
+
+    # Set metadata values.
+    valid_start = "1970-01-01T00:00:00"
+    optics_table.meta.update(
+        {
+            "CALIBDATE": valid_start,
+            "INSTRUME": "comCamSim",
+            "OBSTYPE": "transmission_filter",
+            "TYPE": "transmission_filter",
+            "CALIBCLS": "lsst.ip.isr.IntermediateFilterTransmissionCurve",
+            "SOURCE": "https://github.com/lsst/throughputs",
+            "FILTER": physical_filter,
+            "VERSION": 1.9,
+        }
+    )
+
+    optics_table.meta["CALIB_ID"] = f"calibDate={valid_start} filter={physical_filter}"
+
+    # Write output transmission_filter file.
+    valid_date = dateutil.parser.parse(valid_start)
+    datestr = "".join(re.split(r"[:-]", valid_date.isoformat()))
+
+    data_dir = lsst.utils.getPackageDir("obs_lsst_data")
+    outfile = os.path.join(
+        data_dir, "comCamSim", "transmission_filter", physical_filter, datestr + ".ecsv"
+    )
+    os.makedirs(os.path.dirname(outfile), exist_ok=True)
+
+    curve.writeText(outfile)