C++ Ephemeris

Simple C++ 20 header only library for reading EPM and DE ephemerides. Current version was tested for all DE ephemerides from DE102 to DE441 and for EPM2021 ephemerides. A description of the algorithms used is available in a publication Practical use of EPM and DE ephemeris. Trudy MAI, 2022, no. 125 (in Russian).

Usage

Download ASCII data files for DE or EPM ephemerides:

• Development Ephemeris by JPL.
• Ephemeris of Planets and Moon by IAARAS.

ASCII data files must have't *.txt or *.bin extensions. If there are, rename them. File extensions must match. For example EPM2021 ephemeris have two files: epm2021_de_ascii.txt and header.21. Just rename epm2021_de_ascii.txt to epm2021_de_ascii.21.

#include "eph.h"
int main() {

	/// Set your path to downloaded ASCII data files 
	std::filesystem::path base = "D:\\Projects\\eph\\ascii";

	double x[6] = { 0 };
	/// Test EPM ephemeris
	eph::ephemeris epm;
	/// Import ASCII files from epm2021 folder
	epm.import(base / "epm2021");
	/// Get ephemeris data for Earth
	epm.state(eph::date::jd(2022, 5, 30), eph::targets::earth, x);

	for (auto val : x)
		std::cout << val << std::endl; 
	
	double y[6] = { 0 };
	/// Test DE ephemeris
	eph::ephemeris de;
	/// Import ASCII files from de440t folder
	de.import(base / "de440t");
	/// Get ephemeris data for Earth
	de.state(eph::date::jd(2022, 5, 30), eph::targets::earth, y);

	for (auto val : y)
		std::cout << val << std::endl;

	system("pause");

return 0;
}

Reading ASCII files may be very slow. You may save data to binary file and use it permanently. Binary file also have smaller size.

#include "eph.h"
int main() {

	/// Set your path to downloaded ASCII data files 
	std::filesystem::path base = "D:\\Projects\\eph\\ascii";	
	/// Create ephemeris object
	eph::ephemeris e;
	/// Load from ASCII files and test
	e.import_and_test(base / "de440t");
	/// Save to binary file
	e.save(base / "de440t" / "440t.bin");
	/// Load from binary file
	e.load(base / "de440t" / "440t.bin");

	double state[6] = { 0 };
	/// Get ephemeris data for Earth-Moon Barycenter
	e.state(eph::date::jd(2022, 5, 30), eph::targets::earth_moon_barycenter, state);
	
	for (auto val : state)
		std::cout << val << std::endl;
	
	/// Get ephemeris data using structured binding
	auto [x, y, z, vx, vy, vz] = e.state(eph::date::jd(2022, 5, 30), eph::targets::moon);

	std::cout 
		<< "x = " << x << std::endl
		<< "y = " << y << std::endl
		<< "z = " << z << std::endl
		<< "vx = " << vx << std::endl
		<< "vy = " << vy << std::endl
		<< "vz = " << vz << std::endl;	

	system("pause");

return 0;
}

You can also use the std::chrono dates & time "sugar"

	using namespace std::chrono_literals;
	using namespace std::chrono;	
	
	/// Get ephemeris data using std::chrono format of dates & time
	auto [x, y, z, vx, vy, vz] = e.state(eph::date::jd(May/30/2022, 5h+10min), eph::targets::moon);