New textured moon and rewritten/restructured Astro code contributed by Durk

Talsma.
2009-09-15 18:31:31 +02:00
parent 38631c9eb3
commit 001a2c89e7
33 changed files with 2142 additions and 1524 deletions
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+/**************************************************************************
+ * celestialBody.cxx
+ * Written by Durk Talsma. Originally started October 1997, for distribution  
+ * with the FlightGear project. Version 2 was written in August and 
+ * September 1998. This code is based upon algorithms and data kindly 
+ * provided by Mr. Paul Schlyter. (pausch@saaf.se). 
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id$
+ * (Log is kept at end of this file)
+ **************************************************************************/
+
+#include "celestialBody.hxx"
+#include "star.hxx"
+#include <Debug/fg_debug.h>
+
+/**************************************************************************
+ * void CelestialBody::updatePosition(fgTIME *t, Star *ourSun)
+ *
+ * Basically, this member function provides a general interface for 
+ * calculating the right ascension and declinaion. This function is 
+ * used for calculating the planetary positions. For the planets, an 
+ * overloaded member function is provided to additionally calculate the
+ * planet's magnitude. 
+ * The sun and moon have their own overloaded updatePosition member, as their
+ * position is calculated an a slightly different manner.  
+ *
+ * arguments:
+ * fgTIME t: provides the current time.
+ * Star *ourSun: the sun's position is needed to convert heliocentric 
+ *               coordinates into geocentric coordinates.
+ *
+ * return value: none
+ *
+ *************************************************************************/
+void CelestialBody::updatePosition(fgTIME *t, Star *ourSun)
+{
+  double eccAnom, v, ecl, actTime, 
+    xv, yv, xh, yh, zh, xg, yg, zg, xe, ye, ze;
+
+  updateOrbElements(t);
+  actTime = fgCalcActTime(t);
+
+  // calcualate the angle bewteen ecliptic and equatorial coordinate system
+  ecl = DEG_TO_RAD * (23.4393 - 3.563E-7 *actTime);
+  
+  eccAnom = fgCalcEccAnom(M, e);  //calculate the eccentric anomaly
+  xv = a * (cos(eccAnom) - e);
+  yv = a * (sqrt (1.0 - e*e) * sin(eccAnom));
+  v = atan2(yv, xv);           // the planet's true anomaly
+  r = sqrt (xv*xv + yv*yv);    // the planet's distance
+  
+  // 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));
+
+  // calculate the ecliptic longitude and latitude
+  xg = xh + ourSun->getxs();
+  yg = yh + ourSun->getys();
+  zg = zh;
+  
+  xe = xg;
+  ye = yg * cos(ecl) - zg * sin(ecl);
+  ze = yg * sin(ecl) + zg * cos(ecl);
+  rightAscension = atan2(ye, xe);
+  declination = atan2(ze, sqrt(xe*xe + ye*ye));
+  fgPrintf(FG_GENERAL, FG_INFO, "Planet found at : %f (ra), %f (dec)\n", 
+	   rightAscension, declination);
+
+  //calculate some variables specific to calculating the magnitude 
+  //of the planet
+  R = sqrt (xg*xg + yg*yg + zg*zg);
+  s = ourSun->getDistance();
+  FV = RAD_TO_DEG * acos( (r*r + R*R - s*s) / (2*r*R));
+};
+
+/****************************************************************************
+ * double CelestialBody::fgCalcEccAnom(double M, double e)
+ * this private member calculates the eccentric anomaly of a celestial body, 
+ * given its mean anomaly and eccentricity.
+ * 
+ * -Mean anomaly: the approximate angle between the perihelion and the current
+ *  position. this angle increases uniformly with time.
+ *
+ * True anomaly: the actual angle between perihelion and current position.
+ *
+ * Eccentric anomaly: this is an auxilary angle, used in calculating the true
+ * anomaly from the mean anomaly.
+ * 
+ * -eccentricity. Indicates the amount in which the orbit deviates from a 
+ *  circle (0 = circle, 0-1, is ellipse, 1 = parabola, > 1 = hyperbola).
+ *
+ * This function is also known as solveKeplersEquation()
+ *
+ * arguments: 
+ * M: the mean anomaly
+ * e: the eccentricity
+ *
+ * return value:
+ * the eccentric anomaly
+ *
+ ****************************************************************************/
+double CelestialBody::fgCalcEccAnom(double M, double e)
+{
+  double 
+    eccAnom, E0, E1, diff;
+  
+  eccAnom = M + e * sin(M) * (1.0 + e * cos (M));
+  // iterate to achieve a greater precision for larger eccentricities 
+  if (e > 0.05)
+    {
+      E0 = eccAnom;
+      do
+	{
+	  E1 = E0 - (E0 - e * sin(E0) - M) / (1 - e *cos(E0));
+	  diff = fabs(E0 - E1);
+	  E0 = E1;
+	}
+      while (diff > (DEG_TO_RAD * 0.001));
+      return E0;
+    }
+  return eccAnom;
+}
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