1 | from __future__ import absolute_import
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2 |
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3 | import collections
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4 | import math
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5 | import numpy as np
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6 | import scipy.constants as sc
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7 |
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8 | import common.commonobjects as co
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9 |
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10 | def black_body(temperature, wavenumber):
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11 | """Function to calculate Planck function.
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12 | temperature - Kelvin
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13 | wavenumber - frequency in cm-1
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14 | """
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15 | freq = wavenumber * sc.c * 100.0
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16 | jnu = 2.0 * sc.h * pow(freq,3) / (pow(sc.c,2) *
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17 | (math.exp((sc.h * freq) / (sc.k * temperature)) - 1.0))
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18 |
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19 | return jnu
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20 |
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21 |
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22 | class SkyGenerator(object):
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23 | """Class to generate a model sky.
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24 | """
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25 |
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26 | def __init__(self, parameters, previous_results):
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27 | self.parameters = parameters
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28 | self.previous_results = previous_results
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29 | self.result = collections.OrderedDict()
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30 |
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31 | def run(self):
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32 | print 'SkyGenerator.run'
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33 |
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34 | fts = self.previous_results['fts']
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35 | frequency_axis = fts['fts_wn']
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36 | nspec = len(frequency_axis)
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37 |
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38 | beamsgenerator = self.previous_results['beamsgenerator']
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39 | npix = beamsgenerator['npix']
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40 | spatial_axis = beamsgenerator['spatial axis [arcsec]']
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41 |
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42 | # skymodel is complex so that its fft can hold truncated version
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43 | # of infinitesimally sampled map - does that make sense?
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44 | skymodel = np.zeros([npix, npix, nspec], np.complex)
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45 |
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46 | sky = self.parameters['substages']['Sky']
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47 | columns = sky['SourceNum'].keys()
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48 |
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49 | self.result['sources'] = collections.OrderedDict()
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50 |
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51 | for column in columns:
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52 | temp = sky['SourceNum'][column]
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53 | sourcenum = int(round(temp))
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54 | if sourcenum not in self.result['sources'].keys():
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55 | self.result['sources'][sourcenum] = {}
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56 |
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57 | type = sky['Type'][column]
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58 |
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59 | temp = sky['x pos [asec]'][column]
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60 | xpos = float(temp)
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61 |
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62 | temp = sky['y pos [asec]'][column]
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63 | ypos = float(temp)
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64 |
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65 | temp = sky['Temp'][column]
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66 | temperature = float(temp)
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67 |
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68 | temp = sky['cutoffmin'][column]
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69 | cutoffmin = float(temp)
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70 |
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71 | temp = sky['cutoffmax'][column]
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72 | cutoffmax = float(temp)
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73 |
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74 | temp = sky['emissivity'][column]
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75 | emissivity = float(temp)
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76 |
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77 | print 'generating source:%s type:%s xpos:%s ypos:%s temperature:%s cutoffmin:%s cutoffmax:%s e:%s' % (
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78 | sourcenum, type, xpos, ypos, temperature, cutoffmin, cutoffmax,
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79 | emissivity)
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80 |
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81 | if type.upper().strip() == 'POINT':
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82 | source_spectrum = self._create_point_source(xpos, ypos,
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83 | temperature,
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84 | cutoffmin, cutoffmax, emissivity, skymodel,
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85 | spatial_axis, frequency_axis)
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86 | else:
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87 | source_spectrum = None
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88 | print "source type '%s' not yet implemented" % type
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89 |
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90 | self.result['sources'][sourcenum]['spectrum'] = source_spectrum
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91 |
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92 | self.result['sky model'] = skymodel
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93 | self.result['spatial axis'] = spatial_axis
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94 | self.result['frequency axis'] = frequency_axis
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95 |
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96 | return self.result
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97 |
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98 | def _create_point_source(self, xpos, ypos, temperature, cutoffmin,
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99 | cutoffmax, emissivity, skymodel, spatial_axis, frequency_axis):
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100 | """Create a point source.
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101 | """
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102 |
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103 | # calculate xpos, ypos in units of pixel - numpy arrays [row,col]
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104 | nx = len(spatial_axis)
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105 | colpos = float(nx-1) * float (xpos - spatial_axis[0]) / (spatial_axis[-1] - spatial_axis[0])
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106 | rowpos = float(nx-1) * float (ypos - spatial_axis[0]) / (spatial_axis[-1] - spatial_axis[0])
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107 |
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108 | if colpos < 0 or colpos > (nx-1) or rowpos < 0 or rowpos > (nx-1):
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109 | # point source is outside modelled area
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110 | return
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111 |
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112 | # calculate fourier phase shift to move point at [0,0] to
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113 | # [rowpos, colpos]
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114 | shiftx = np.zeros([nx], np.complex)
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115 | shiftx[:nx/2] = np.arange(nx/2, dtype=np.complex)
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116 | shiftx[nx/2:] = np.arange(-nx/2, 0, dtype=np.complex)
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117 | shiftx = np.exp((-2.0j * np.pi * colpos * shiftx) / float(nx))
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118 |
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119 | shifty = np.zeros([nx], np.complex)
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120 | shifty[:nx/2] = np.arange(nx/2, dtype=np.complex)
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121 | shifty[nx/2:] = np.arange(-nx/2, 0, dtype=np.complex)
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122 | shifty = np.exp((-2.0j * np.pi * rowpos * shifty) / float(nx))
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123 |
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124 | shift = np.ones([nx,nx], np.complex)
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125 | for j in range(nx):
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126 | shift[j,:] *= shiftx
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127 | for i in range(nx):
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128 | shift[:,i] *= shifty
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129 |
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130 | # calculate black-body spectrum, modified for cutoffs in
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131 | # sensitivity and source emissivity
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132 | bbmod = np.zeros(np.shape(frequency_axis))
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133 | # ignore floating point errors
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134 | old_settings = np.seterr(all='ignore')
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135 | for iwn,wn in enumerate(frequency_axis):
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136 | # simulate real-life 'rounded' cutoffs numerically
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137 | f1 = 1.0 / (1.0 + pow(cutoffmin/wn, 18) + pow(wn/cutoffmax, 24))
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138 | bbmod[iwn] = black_body(temperature, wn) * f1 * emissivity
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139 | # restore fp behaviour
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140 | ignore = np.seterr(**old_settings)
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141 |
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142 | # go through freq planes and add point source to each
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143 | for iwn,wn in enumerate(frequency_axis):
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144 | # create point in frequency space
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145 | temp = np.zeros([nx,nx])
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146 | temp[0,0] = bbmod[iwn]
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147 | # 2d fft
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148 | temp = np.fft.fft2(temp)
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149 | # apply phase shift to move point to required offset
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150 | temp *= shift
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151 | # transform back
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152 | temp = np.fft.ifft2(temp)
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153 | temp = np.real(temp)
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154 |
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155 | # add to sky model
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156 | skymodel[:,:,iwn] += temp
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157 |
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158 | # return spectrum
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159 | axis = co.Axis(data=frequency_axis, title='wavenumber', units='cm-1')
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160 | spectrum = co.Spectrum(data=bbmod, axis=axis, title='Source spectrum',
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161 | units='W sr-1 m-2 Hz-1')
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162 |
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163 | return spectrum
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164 |
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165 | def __repr__(self):
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166 | return 'SkyGenerator'
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167 |
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