FGFS-4.1/simgear
4
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Optimisation of the celestialBody ephemeris code.

Browse Source 
By storing repetitive intermediate calculations, the number of mathematical
operations for a single call to CelestialBody::updatePosition() has decreased by
12.  This matches the changes to MoonPos::updatePosition().
This commit is contained in:
Edward d'Auvergne 2015-12-07 21:03:33 +01:00
parent f04e501472
commit edcd42bc2d
1 changed files with 16 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
simgear/ephemeris/celestialBody.cxx
View File

@ -52,7 +52,8 @@
void CelestialBody::updatePosition(double mjd, Star *ourSun)
{
double eccAnom, v, ecl, actTime,
xv, yv, xh, yh, zh, xg, yg, zg, xe, ye, ze;
xv, yv, xh, yh, zh, xg, yg, zg, xe, ye, ze,
cosN, sinN, cosvw, sinvw, sinvw_cosi, cosecl, sinecl;
updateOrbElements(mjd);
actTime = sgCalcActTime(mjd);
@ -66,10 +67,19 @@ void CelestialBody::updatePosition(double mjd, Star *ourSun)
v = atan2(yv, xv); // the planet's true anomaly
r = sqrt (xv*xv + yv*yv); // the planet's distance
// repetitive calculations, minimised for speed
cosN = cos(N);
sinN = sin(N);
cosvw = cos(v+w);
sinvw = sin(v+w);
sinvw_cosi = sinvw * cos(i);
cosecl = cos(ecl);
sinecl = sin(ecl);
// calculate the planet's position in 3D space
xh = r * (cos(N) * cos(v+w) - sin(N) * sin(v+w) * cos(i));
yh = r * (sin(N) * cos(v+w) + cos(N) * sin(v+w) * cos(i));
zh = r * (sin(v+w) * sin(i));
xh = r * (cosN * cosvw - sinN * sinvw_cosi);
yh = r * (sinN * cosvw + cosN * sinvw_cosi);
zh = r * (sinvw * sin(i));
// calculate the ecliptic longitude and latitude
xg = xh + ourSun->getxs();
@ -80,8 +90,8 @@ void CelestialBody::updatePosition(double mjd, Star *ourSun)
latEcl = atan2(zh, sqrt(xh*xh+yh*yh));
xe = xg;
ye = yg * cos(ecl) - zg * sin(ecl);
ze = yg * sin(ecl) + zg * cos(ecl);
ye = yg * cosecl - zg * sinecl;
ze = yg * sinecl + zg * cosecl;
rightAscension = atan2(ye, xe);
declination = atan2(ze, sqrt(xe*xe + ye*ye));
/* SG_LOG(SG_GENERAL, SG_INFO, "Planet found at : "