feat: calculate mean orbital motion from M

This commit is contained in:
Cat Flynn 2024-08-21 15:45:33 +01:00
parent 8d6138f15e
commit a570986485
9 changed files with 47 additions and 38 deletions

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@ -24,16 +24,9 @@ public:
void setArgumentOfPeriapsis(double argumentOfPeriapsis);
void setLongitudeOfAscendingNode(double longitudeOfAscendingNode);
// TODO: meanAnomaly in all these arguments actually means ellipticalMeanAnomaly,
// will have to change that when adding non-ellipctical orbits - don't get confused!
//
// do we actual want to use mean anomaly for this? we could instead pass in time and
// the gravitational parameter which are easier numbers to come by, i think? at least,
// the mean motion is determined from the mean motion and time time
//glm::vec3 getPosition(double gravitationalParameter, double time) const;
glm::dvec3 getPosition(const double meanAnomaly) const;
glm::dvec3 getTangent(const double meanAnomaly) const;
glm::dvec3 getPosition(double gravitationalParameter, double time) const;
glm::dvec3 getPositionFromMeanAnomaly(double meanAnomaly) const;
//glm::dvec3 getTangent(const double meanAnomaly) const;
//glm::mat4 getLookAlongMatrix(const double meanAnomaly) const;
private:

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@ -13,6 +13,7 @@ public:
const std::string& getId() const;
double getMass() const;
double getGravitationalParameter() const;
private:
const std::string _id;

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@ -22,6 +22,7 @@ class ParticleMap
private:
std::map<std::string, Particle> _particles;
// TODO: improve on this very vague name
std::map<std::string, std::string> _relationships;
std::map<std::string, Orbit> _orbits;
};

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@ -2,6 +2,7 @@
#include "astro/stateVectorIndices.hpp"
#include "astro/orbitalElementConversions.hpp"
#include "astro/twoBodyMethods.hpp"
#include <glm/gtc/matrix_transform.hpp>
@ -87,9 +88,7 @@ const double Orbit::getEccentricAnomaly(const double meanAnomaly) const
return eccentricAnomaly;
}
// Interpolate a position around the orbit.
// t is in range 0..1 and wraps.
glm::dvec3 Orbit::getPosition(const double meanAnomaly) const
glm::dvec3 Orbit::getPositionFromMeanAnomaly(const double meanAnomaly) const
{
Vector6 cartesian = getCartesianCoordinates(meanAnomaly);
return glm::dvec3(
@ -98,6 +97,13 @@ glm::dvec3 Orbit::getPosition(const double meanAnomaly) const
cartesian[astro::zPositionIndex]);
}
glm::dvec3 Orbit::getPosition(double gravitationalParameter, double time) const
{
double meanMotion = astro::computeKeplerMeanMotion(getSemiMajorAxis(), gravitationalParameter);
double meanAnomaly = meanMotion * time;
return getPositionFromMeanAnomaly(meanAnomaly);
}
const double Orbit::getTrueAnomaly(const double meanAnomaly) const
{
const double eccentricAnomaly = getEccentricAnomaly(meanAnomaly);
@ -114,11 +120,11 @@ const Vector6 Orbit::getCartesianCoordinates(const double meanAnomaly) const
return astro::convertKeplerianToCartesianElements(kepler, 1.0);
}
glm::dvec3 Orbit::getTangent(const double meanAnomaly) const
{
double epsilon = 0.01;
glm::dvec3 ahead = getPosition(meanAnomaly + epsilon);
glm::dvec3 behind = getPosition(meanAnomaly - epsilon);
return glm::normalize(ahead - behind);
}
//glm::dvec3 Orbit::getTangent(const double meanAnomaly) const
//{
// double epsilon = 0.01;
// glm::dvec3 ahead = getPosition(meanAnomaly + epsilon);
// glm::dvec3 behind = getPosition(meanAnomaly - epsilon);
// return glm::normalize(ahead - behind);
//}

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@ -1,5 +1,7 @@
#include "skein/particle.h"
#include <astro/constants.hpp>
Particle::Particle(const std::string& id, double mass)
: _id(id), _mass(mass)
{
@ -19,3 +21,8 @@ double Particle::getMass() const
{
return _mass;
}
double Particle::getGravitationalParameter() const
{
return _mass * astro::ASTRO_GRAVITATIONAL_CONSTANT;
}

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@ -1,7 +1,6 @@
#include "skein/particlemap.h"
#include "skein/particle.h"
const Particle& ParticleMap::getParticle(const std::string& id) const
{
return _particles.at(id);
@ -17,20 +16,13 @@ glm::dvec3 ParticleMap::getParticlePosition(const std::string& id, double time)
if (_orbits.find(id) == _orbits.end())
return {0,0,0};
// TODO: actually get stuff based on physics
//const Particle& parent = _relationships.at(id);
// how do we get the gravitational parameter?
// is it just G * M
// where M is the mass of the parent
//const double u = getGravitationalParameter(parent.getId());
//const double mass = parent.getMass();
// how do we get the particle position from the time + gravitational parameter?
const std::string& parentId = _relationships.at(id);
const Particle& parent = _particles.at(parentId);
const double gravitationalParameter = parent.getGravitationalParameter();
// TODO: actually nest stuff so position is determined from all parents
const Orbit& orbit = _orbits.at(id);
return orbit.getPosition(time);
return orbit.getPosition(gravitationalParameter, time);
}
void ParticleMap::setParticle(const Particle& particle)

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@ -128,7 +128,9 @@ void updateViewMatrix(GLuint shaderProgram, float time)
glm::mat4 view = glm::mat4(1.0);
// Rotation
constexpr float angle = glm::radians(10.0);
// TODO: disconnect application and simulation time
constexpr float angle = 0;
//constexpr float angle = glm::radians(10.0);
glm::vec3 axis = glm::vec3(0.0, 1.0, 0.0);
view = glm::rotate(view, angle * time, axis);

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@ -103,10 +103,10 @@ int main()
// set parameters of moon's orbit around earth
Orbit orbit;
double semiMajorAxis = 3.84748e9;
double semiMajorAxis = 3.84748e8;
orbit.setSemiMajorAxis(semiMajorAxis); // metres
orbit.setEccentricity(0.055);
orbit.setInclination(glm::radians(5.15)); // radians?
orbit.setInclination(glm::radians(5.15)); // radians
orbit.setArgumentOfPeriapsis(318.15); // in the case of the moon these last two values are
orbit.setLongitudeOfAscendingNode(60.0); // pretty much constantly changing so use whatever
@ -149,8 +149,11 @@ int main()
}
}
// the moon takes like 27 days to orbit earth. to see this in motion, then, we need to
// increase the speed of time by 60 * 60 * 24 to see 1 day per second.
const double speed = 60 * 60 * 24;
// only update time if playing the orbiting animation
const double speed = 0.5;
if (animation == ANIM_ORBITING)
{
time = getTime() * speed;

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@ -27,8 +27,12 @@ void OrbitVisualizer::regenerateVertices()
for (int i = 0; i < _vertexCount; i++)
{
// TODO: this method of getting ellipse vertices is a huge hack. it would be
// better to actually create a first-class ellipse object and use that to generate
// a nice continuous mesh, instead of using orbital positions.
float t = (float)i / (float)_vertexCount * 2.0 * _pi;
glm::vec3 pos = _orbit.getPosition(t);
glm::vec3 pos = _orbit.getPositionFromMeanAnomaly(t);
// Vertices come out of the library with X and Y being in the 'flat' plane. Re-order them
// here such that Z is up.
float y = pos.z;