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375 lines
15 KiB
C++
375 lines
15 KiB
C++
/*****************************************************************************************
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* *
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* OpenSpace *
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* *
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* Copyright (c) 2014-2016 *
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* *
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this *
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* software and associated documentation files (the "Software"), to deal in the Software *
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* without restriction, including without limitation the rights to use, copy, modify, *
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* merge, publish, distribute, sublicense, and/or sell copies of the Software, and to *
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* permit persons to whom the Software is furnished to do so, subject to the following *
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* conditions: *
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* *
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* The above copyright notice and this permission notice shall be included in all copies *
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* or substantial portions of the Software. *
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* *
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, *
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* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A *
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* PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT *
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF *
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* CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE *
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* OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. *
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****************************************************************************************/
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#include <modules/base/translation/tletranslation.h>
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#include <openspace/documentation/verifier.h>
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#include <ghoul/filesystem/filesystem.h>
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#include <ghoul/misc/assert.h>
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#include <chrono>
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#include <fstream>
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#include <vector>
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namespace {
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const char* KeyFile = "File";
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// The list of leap years only goes until 2056 as we need to touch this file then
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// again anyway ;)
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static const std::vector<int> LeapYears = {
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1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996,
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2000, 2004, 2008, 2012, 2016, 2020, 2024, 2028, 2032, 2036, 2040,
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2044, 2048, 2052, 2056
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};
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// Count the number of full days since the beginning of 2000 to the beginning of
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// the parameter 'year'
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int countDays(int year) {
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// Find the position of the current year in the vector, the difference
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// between its position and the position of 2000 (for J2000) gives the
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// number of leap years
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const int Epoch = 2000;
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const int DaysRegularYear = 365;
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const int DaysLeapYear = 366;
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if (year == Epoch) {
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return 0;
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}
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// Get the position of the most recent leap year
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auto lb = std::lower_bound(LeapYears.begin(), LeapYears.end(), year);
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// Get the position of the epoch
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auto y2000 = std::find(LeapYears.begin(), LeapYears.end(), Epoch);
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// The distance between the two iterators gives us the number of leap years
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int nLeapYears = std::abs(std::distance(y2000, lb));
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int nYears = std::abs(year - Epoch);
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int nRegularYears = nYears - nLeapYears;
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// Get the total number of days as the sum of leap years + non leap years
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int result = nRegularYears * DaysRegularYear + nLeapYears * DaysLeapYear;
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return result;
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};
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// Returns the number of leap seconds that lie between the {year, dayOfYear}
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// time point and { 2000, 1 }
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int countLeapSeconds(int year, int dayOfYear) {
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// Find the position of the current year in the vector; its position in
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// the vector gives the number of leap seconds
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struct LeapSecond {
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int year;
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int dayOfYear;
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bool operator<(const LeapSecond& rhs) const {
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return
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std::tie(year, dayOfYear) < std::tie(rhs.year, rhs.dayOfYear);
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}
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};
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const LeapSecond Epoch = { 2000, 1};
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// List taken from: https://www.ietf.org/timezones/data/leap-seconds.list
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static const std::vector<LeapSecond> LeapSeconds = {
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{ 1972, 1 },
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{ 1972, 183 },
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{ 1973, 1 },
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{ 1974, 1 },
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{ 1975, 1 },
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{ 1976, 1 },
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{ 1977, 1 },
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{ 1978, 1 },
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{ 1979, 1 },
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{ 1980, 1 },
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{ 1981, 182 },
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{ 1982, 182 },
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{ 1983, 182 },
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{ 1985, 182 },
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{ 1988, 1 },
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{ 1990, 1 },
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{ 1991, 1 },
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{ 1992, 183 },
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{ 1993, 182 },
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{ 1994, 182 },
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{ 1996, 1 },
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{ 1997, 182 },
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{ 1999, 1 },
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{ 2006, 1 },
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{ 2009, 1 },
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{ 2012, 183 },
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{ 2015, 182 },
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{ 2017, 1 }
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};
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// Get the position of the last leap second before the desired date
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LeapSecond date { year, dayOfYear };
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auto it = std::lower_bound(LeapSeconds.begin(), LeapSeconds.end(), date);
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// Get the position of the Epoch
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auto y2000 = std::lower_bound(LeapSeconds.begin(), LeapSeconds.end(), Epoch);
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// The distance between the two iterators gives us the number of leap years
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int nLeapSeconds = std::abs(std::distance(y2000, it));
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return nLeapSeconds;
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};
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double epochFromSubstring(const std::string& epochString) {
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// The epochString is in the form:
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// YYDDD.DDDDDDDD
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// With YY being the last two years of the launch epoch, the first DDD the day
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// of the year and the remaning a fractional part of the day
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// The main overview of this function:
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// 1. Reconstruct the full year from the YY part
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// 2. Calculate the number of seconds since the beginning of the year
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// 2.a Get the number of full days since the beginning of the year
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// 2.b If the year is a leap year, modify the number of days
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// 3. Convert the number of days to a number of seconds
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// 4. Get the number of leap seconds since January 1st, 2000 and remove them
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// 5. Adjust for the fact the epoch starts on 1st Januaray at 12:00:00, not
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// midnight
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// According to https://celestrak.com/columns/v04n03/
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// Apparently, US Space Command sees no need to change the two-line element
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// set format yet since no artificial earth satellites existed prior to 1957.
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// By their reasoning, two-digit years from 57-99 correspond to 1957-1999 and
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// those from 00-56 correspond to 2000-2056. We'll see each other again in 2057!
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// 1. Get the full year
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std::string yearPrefix = [y = epochString.substr(0, 2)](){
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int year = std::atoi(y.c_str());
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return year >= 57 ? "19" : "20";
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}();
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int year = std::atoi((yearPrefix + epochString.substr(0, 2)).c_str());
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int daysSince2000 = countDays(year);
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// 2.
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// 2.a
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double daysInYear = std::atof(epochString.substr(2).c_str());
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// 2.b
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bool isInLeapYear = std::find(
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LeapYears.begin(),
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LeapYears.end(),
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year
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) != LeapYears.end();
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if (isInLeapYear && daysInYear >= 60) {
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// We are in a leap year, so we have an effective day more if we are
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// beyond the end of february (= 31+29 days)
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--daysInYear;
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}
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// 3
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using namespace std::chrono;
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int SecondsPerDay = seconds(hours(24)).count();
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double nSecondsSince2000 = (daysSince2000 + daysInYear) * SecondsPerDay;
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// 4
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// We need to remove additionbal leap seconds past 2000 and add them prior to
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// 2000 to sync up the time zones
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double nLeapSecondsOffset = -countLeapSeconds(year, std::floor(daysInYear));
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// 5
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double nSecondsEpochOffset = seconds(hours(12)).count();
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// Combine all of the values
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double epoch = nSecondsSince2000 + nLeapSecondsOffset - nSecondsEpochOffset;
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return epoch;
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}
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double calculateSemiMajorAxis(double meanMotion) {
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using namespace std::chrono;
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const double GravitationalConstant = 6.6740831e-11;
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const double MassEarth = 5.9721986e24;
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const double muEarth = GravitationalConstant * MassEarth;
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// Use Kepler's 3rd law to calculate semimajor axis
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// a^3 / P^2 = mu / (2pi)^2
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// <=> a = ((mu * P^2) / (2pi^2))^(1/3)
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// with a = semimajor axis
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// P = period in seconds
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// mu = G*M_earth
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using namespace std::chrono;
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double period = seconds(hours(24)).count() / meanMotion;
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const double pisq = glm::pi<double>() * glm::pi<double>();
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double semiMajorAxis = pow((muEarth * period*period) / (4 * pisq), 1.0 / 3.0);
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// We need the semi major axis in km instead of m
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return semiMajorAxis / 1000.0;
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}
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}
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namespace openspace {
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Documentation TLETranslation::Documentation() {
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using namespace openspace::documentation;
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return {
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"TLE Translation",
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"base_transform_tle",
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{
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{
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"Type",
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new StringEqualVerifier("TLETranslation"),
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"",
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Optional::No
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},
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{
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KeyFile,
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new StringVerifier,
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"Specifies the filename of the Two-Line-Element file",
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Optional::No
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}
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},
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Exhaustive::No
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};
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}
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TLETranslation::TLETranslation(const ghoul::Dictionary& dictionary)
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: KeplerTranslation()
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{
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documentation::testSpecificationAndThrow(
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Documentation(),
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dictionary,
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"TLETranslation"
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);
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std::string file = dictionary.value<std::string>(KeyFile);
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readTLEFile(file);
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}
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void TLETranslation::readTLEFile(const std::string& filename) {
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ghoul_assert(FileSys.fileExists(filename), "The filename must exist");
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std::ifstream file;
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file.exceptions(std::ofstream::failbit | std::ofstream::badbit);
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file.open(filename);
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// All of the Kepler element information
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struct {
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double inclination;
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double semiMajorAxis;
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double ascendingNode;
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double eccentricity;
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double argumentOfPeriapsis;
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double meanAnomaly;
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double meanMotion;
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double epoch;
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} keplerElements;
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std::string line;
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while (std::getline(file, line)) {
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if (line[0] == '1') {
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// First line
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// Field Columns Content
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// 1 01-01 Line number
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// 2 03-07 Satellite number
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// 3 08-08 Classification (U = Unclassified)
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// 4 10-11 International Designator (Last two digits of launch year)
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// 5 12-14 International Designator (Launch number of the year)
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// 6 15-17 International Designator(piece of the launch) A
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// 7 19-20 Epoch Year(last two digits of year)
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// 8 21-32 Epoch(day of the year and fractional portion of the day)
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// 9 34-43 First Time Derivative of the Mean Motion divided by two
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// 10 45-52 Second Time Derivative of Mean Motion divided by six
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// 11 54-61 BSTAR drag term(decimal point assumed)[10] - 11606 - 4
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// 12 63-63 The "Ephemeris type"
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// 13 65-68 Element set number.Incremented when a new TLE is generated
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// 14 69-69 Checksum (modulo 10)
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keplerElements.epoch = epochFromSubstring(line.substr(18, 14));
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}
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else if (line[0] == '2') {
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// Second line
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//Field Columns Content
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// 1 01-01 Line number
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// 2 03-07 Satellite number
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// 3 09-16 Inclination (degrees)
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// 4 18-25 Right ascension of the ascending node (degrees)
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// 5 27-33 Eccentricity (decimal point assumed)
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// 6 35-42 Argument of perigee (degrees)
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// 7 44-51 Mean Anomaly (degrees)
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// 8 53-63 Mean Motion (revolutions per day)
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// 9 64-68 Revolution number at epoch (revolutions)
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// 10 69-69 Checksum (modulo 10)
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std::stringstream stream;
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stream.exceptions(std::ios::failbit);
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// Get inclination
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stream.str(line.substr(8, 8));
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stream >> keplerElements.inclination;
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stream.clear();
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// Get Right ascension of the ascending node
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stream.str(line.substr(17, 8));
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stream >> keplerElements.ascendingNode;
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stream.clear();
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// Get Eccentricity
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stream.str("0." + line.substr(26, 7));
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stream >> keplerElements.eccentricity;
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stream.clear();
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// Get argument of periapsis
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stream.str(line.substr(34, 8));
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stream >> keplerElements.argumentOfPeriapsis;
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stream.clear();
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// Get mean anomaly
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stream.str(line.substr(43, 8));
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stream >> keplerElements.meanAnomaly;
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stream.clear();
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// Get mean motion
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stream.str(line.substr(52, 11));
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stream >> keplerElements.meanMotion;
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break;
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}
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}
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// Calculate the semi major axis based on the mean motion using kepler's laws
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keplerElements.semiMajorAxis = calculateSemiMajorAxis(keplerElements.meanMotion);
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// Converting the mean motion (revolutions per day) to period (seconds per revolution)
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using namespace std::chrono;
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double period = seconds(hours(24)).count() / keplerElements.meanMotion;
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setKeplerElements(
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keplerElements.eccentricity,
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keplerElements.semiMajorAxis,
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keplerElements.inclination,
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keplerElements.ascendingNode,
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keplerElements.argumentOfPeriapsis,
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keplerElements.meanAnomaly,
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period,
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keplerElements.epoch
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);
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}
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} // namespace openspace
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