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1# LSST Data Management System 

2# Copyright 2016 AURA/LSST. 

3# 

4# This product includes software developed by the 

5# LSST Project (http://www.lsst.org/). 

6# 

7# This program is free software: you can redistribute it and/or modify 

8# it under the terms of the GNU General Public License as published by 

9# the Free Software Foundation, either version 3 of the License, or 

10# (at your option) any later version. 

11# 

12# This program is distributed in the hope that it will be useful, 

13# but WITHOUT ANY WARRANTY; without even the implied warranty of 

14# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 

15# GNU General Public License for more details. 

16# 

17# You should have received a copy of the LSST License Statement and 

18# the GNU General Public License along with this program. If not, 

19# see <https://www.lsstcorp.org/LegalNotices/>. 

20 

21 

22import numpy as np 

23import astropy.units as u 

24 

25from lsst.verify import Measurement, Datum 

26 

27 

28def measurePA2(metric, pa1, pf1_thresh): 

29 """Measurement of PA2: millimag from median RMS (see PA1) of which 

30 PF1 of the samples can be found. 

31 

32 Parameters 

33 ---------- 

34 metric : `lsst.verify.Metric` 

35 A PA2 `~lsst.verify.Metric` instance. 

36 pa1 : `lsst.verify.Measurement` 

37 A PA1 measurement instance. 

38 pf1_thresh : `astropy.units.Quantity` 

39 Quantity specifying the threshold at which to calculate PA2 

40 

41 Returns 

42 ------- 

43 measurement : `lsst.verify.Measurement` 

44 Measurement of PA2 and associated metadata. 

45 

46 Notes 

47 ----- 

48 The LSST Science Requirements Document (LPM-17) is commonly referred 

49 to as the SRD. The SRD puts a limit that no more than PF1 % of difference 

50 will vary by more than PA2 millimag. The design, minimum, and stretch 

51 goals are PF1 = (10, 20, 5) % at PA2 = (15, 15, 10) millimag following 

52 LPM-17 as of 2011-07-06, available at http://ls.st/LPM-17. 

53 """ 

54 

55 datums = {} 

56 datums['pf1_thresh'] = Datum(quantity=pf1_thresh, description="Threshold from the PF1 specification") 

57 

58 # Use first random sample from original PA1 measurement 

59 magDiffs = pa1.extras['magDiff'].quantity[0, :] 

60 

61 pf1Percentile = 100.*u.percent - pf1_thresh 

62 return Measurement(metric, np.percentile(np.abs(magDiffs.value), pf1Percentile.value) * magDiffs.unit, 

63 extras=datums)