1 | # Various utilities
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2 |
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3 | import math
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4 |
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5 | #------------------------------------------------------------------------------
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6 |
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7 | # The average of the radius at the poles and a the equator, in metres
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8 | #EARTH_RADIUS=6367467.4
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9 | EARTH_RADIUS=6371000
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10 | #EARTH_RADIUS=6378137
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11 |
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12 | #------------------------------------------------------------------------------
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13 |
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14 | def getDegMinSec(degrees):
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15 | """Break up the given floating point degrees value into a tuple.
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16 |
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17 | The tuple contains 4 items:
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18 | - the degrees as an integer
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19 | - the minutes as an integer
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20 | - the seconds as an integer
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21 | - 1.0 if the value was non-negative, -1.0 if it was negative."""
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22 |
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23 | if degrees<0:
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24 | degrees = -degrees
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25 | mul = -1.0
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26 | else:
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27 | mul = 1.0
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28 |
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29 | deg = int(degrees)
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30 | min = int((degrees*60.0)%60.0)
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31 | sec = int((degrees*3600.0)%60.0)
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32 |
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33 | return (deg, min, sec, mul)
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34 |
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35 | #------------------------------------------------------------------------------
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36 |
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37 | def getCoordinateString((latitude, longitude)):
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38 | """Get the string representation of the given coordinate pair."""
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39 |
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40 | latitude_str = getLatitudeString(latitude)
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41 | longitude_str = getLongitudeString(longitude)
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42 |
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43 | return latitude_str + " " + longitude_str
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44 |
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45 | #------------------------------------------------------------------------------
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46 |
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47 | def getLatitudeString(latitude):
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48 | """Get a string representation of the given latitude."""
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49 | return getDegreeString(latitude, ["N", "S"])
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50 |
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51 | #------------------------------------------------------------------------------
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52 |
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53 | def getLongitudeString(longitude):
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54 | """Get a string representation of the given longitude."""
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55 |
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56 | return getDegreeString(longitude, ["E", "W"])
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57 |
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58 | #------------------------------------------------------------------------------
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59 |
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60 | def getDegreeString(degree, prefixes):
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61 | """Get a string representation of the given degree.
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62 |
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63 | If the sign is positive, prefixes[0], otherwise prefixes[1] will be
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64 | prepended to the string."""
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65 |
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66 | if degree<0:
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67 | prefix = prefixes[1]
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68 | else:
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69 | prefix = prefixes[0]
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70 |
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71 | (deg, min, sec, _sign) = getDegMinSec(degree)
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72 |
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73 | return u"%s%d\u00b0%02d\u2032%02d\u2033" % (prefix, deg, min, sec)
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74 |
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75 | #------------------------------------------------------------------------------
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76 |
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77 | def getTimeIntervalString(seconds):
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78 | """Get a more human-friendly representation of the given time interval
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79 | expressed in seconds."""
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80 | hours = int(seconds / 3600)
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81 | minutes = int((seconds / 60) % 60)
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82 | seconds = int(seconds % 60)
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83 | return "%d:%02d:%02d" % (hours, minutes, seconds)
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84 |
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85 | #------------------------------------------------------------------------------
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86 |
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87 | def km2nm(km):
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88 | """Convert the given kilometres into nautical miles."""
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89 | return km/1.852
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90 |
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91 | #------------------------------------------------------------------------------
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92 |
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93 | def nm2km(nm):
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94 | """Convert the given nautical miles into kilometres."""
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95 | return nm*1.852
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96 |
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97 | #------------------------------------------------------------------------------
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98 |
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99 | def radians2km(radians):
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100 | """Convert the given radians into kilometres"""
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101 | return radians * EARTH_RADIUS / 1000.0
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102 |
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103 | #------------------------------------------------------------------------------
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104 |
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105 | def radians2nm(radians):
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106 | """Convert the given radians into nautical miles."""
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107 | return km2nm(radians2km(radians))
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108 |
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109 | #------------------------------------------------------------------------------
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110 |
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111 | def getDistCourse(latitude1, longitude1, latitude2, longitude2):
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112 | """Get the distance and course between the two geographical coordinates.
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113 |
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114 | This function calculates the rhumb distance."""
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115 |
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116 | latitude1 = math.radians(latitude1)
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117 | longitude1 = math.radians(longitude1)
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118 |
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119 | latitude2 = math.radians(latitude2)
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120 | longitude2 = math.radians(longitude2)
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121 |
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122 | dlon_W = (longitude1 - longitude2) % (math.pi*2)
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123 | dlon_E = (longitude2 - longitude1) % (math.pi*2)
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124 |
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125 | dphi = math.log(math.tan(latitude2/2 + math.pi/4)/
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126 | math.tan(latitude1/2 + math.pi/4))
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127 |
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128 | if abs(latitude1-latitude2) < math.sqrt(1e-15):
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129 | q = math.cos(latitude1)
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130 | else:
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131 | q = (latitude1-latitude2)/dphi
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132 |
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133 | if dlon_W < dlon_E:
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134 | tc = math.atan2(-dlon_W, dphi) % (math.pi*2)
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135 | d = math.sqrt(math.pow(q*dlon_W, 2) +
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136 | math.pow(latitude1-latitude2, 2))
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137 | else:
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138 | tc = math.atan2(dlon_E, dphi) % (math.pi*2)
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139 | d = math.sqrt(math.pow(q*dlon_E, 2) +
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140 | math.pow(latitude1-latitude2, 2))
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141 |
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142 | return (radians2nm(d), math.degrees(tc))
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143 |
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