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/******************************************************************************
Xplanet 0.43 - render an image of the earth into an X window
Copyright (C) 1999 Hari Nair <hari@alumni.caltech.edu>
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
******************************************************************************/
#include <math.h>
#include <time.h>
#include <sys/time.h>
extern const float deg_to_rad = M_PI/180.;
extern const float TWO_PI = 2 * M_PI;
double
poly (double a1, double a2, double a3, double a4, double t)
{
return(a1 + t*(a2 + t*(a3 + t*a4)));
}
double
julian (int year, int month, int day, int hour, int min, int sec)
{
int a, b, c, d;
double e, jd;
if(month < 3)
{
year -= 1;
month += 12;
}
// assume it's the Gregorian calendar (after 1582 Oct 15)
a = year/100;
b = 2 - a + a/4;
c = int (365.25 * year);
d = int (30.6001 * (month + 1));
e = day + hour/24. + min/1400. + sec/86400.;
jd = b + c + d + e + 1720994.5;
return jd;
}
double
jcentury (time_t tv_sec)
{
double jd = julian (gmtime (&tv_sec)->tm_year + 1900,
gmtime (&tv_sec)->tm_mon + 1,
gmtime (&tv_sec)->tm_mday,
gmtime (&tv_sec)->tm_hour,
gmtime (&tv_sec)->tm_min,
gmtime (&tv_sec)->tm_sec);
return ((jd - 2415020)/36525);
}
double
kepler (double e, double M)
{
double E = M;
double delta = 1;
while ( fabs (delta) > 1E-10 )
{
delta = (M + e * sin (E) - E)/(1 - e * cos (E));
E += delta;
}
return (E);
}
double
gmst (double T, time_t tv_sec)
{
// Sidereal time at Greenwich at 0 UT
double g = poly (6.6460656, 2400.051262, 0.00002581, 0, T);
// Now find current sidereal time at Greenwich
double currgmt = (gmtime (&tv_sec)->tm_hour
+ gmtime (&tv_sec)->tm_min/60.
+ gmtime (&tv_sec)->tm_sec/3600.);
currgmt *= 1.002737908;
g += currgmt;
g = fmod (g, 24.0);
if (g < 0) g += 24;
return (g);
}
double
compute_obliquity ( double T )
{
return (poly (23.452294, -1.30125E-2, -1.64E-6, 5.03E-7, T)
* deg_to_rad);
}
void
compute_ra_dec (double lon, double lat, double &alpha,
double &delta, double eps)
{
delta = asin (sin (eps) * sin (lon) * cos (lat) + sin (lat) * cos (eps));
alpha = (atan2 (cos (eps) * sin (lon) - tan (lat) * sin (eps), cos (lon))
/ deg_to_rad);
alpha /= 15;
alpha = fmod (alpha, 24.0);
if (alpha < 0) alpha += 24;
}
void rotate_xyz (double matrix[3][3], float angle_x,
float angle_y, float angle_z)
{
/*
matrix to first rotate reference frame angle_x radians through
x axis, then angle_y radians through y axis, and lastly
angle_z radians through z axis. Positive rotations are counter-
clockwise looking down the axis.
*/
matrix[0][0] = cos(angle_y) * cos(angle_z);
matrix[0][1] = (sin(angle_x) * sin(angle_y) * cos(angle_z)
+ cos(angle_x) * sin(angle_z));
matrix[0][2] = (-cos(angle_x) * sin(angle_y) * cos(angle_z) +
sin(angle_x) * sin(angle_z));
matrix[1][0] = -cos(angle_y) * sin(angle_z);
matrix[1][1] = (-sin(angle_x) * sin(angle_y) * sin(angle_z)
+ cos(angle_x) * cos(angle_z));
matrix[1][2] = (cos(angle_x) * sin(angle_y) * sin(angle_z)
+ sin(angle_x) * cos(angle_z));
matrix[2][0] = sin(angle_y);
matrix[2][1] = -sin(angle_x) * cos(angle_y);
matrix[2][2] = cos(angle_x) * cos(angle_y);
}
void rotate_zyx (double matrix[3][3], float angle_x,
float angle_y, float angle_z)
{
/*
matrix to first rotate reference frame angle_z radians through
z axis, then angle_y radians through y axis, and lastly
angle_x radians through x axis. Positive rotations are counter-
clockwise looking down the axis.
*/
matrix[0][0] = cos(angle_y) * cos(angle_z);
matrix[0][1] = cos(angle_y) * sin(angle_z);
matrix[0][2] = -sin(angle_y);
matrix[1][0] = (-cos(angle_x) * sin(angle_z)
+ sin(angle_x) * sin(angle_y) * cos(angle_z));
matrix[1][1] = (sin(angle_x) * sin(angle_y) * sin(angle_z)
+ cos(angle_x) * cos(angle_z));
matrix[1][2] = sin(angle_x) * cos(angle_y);
matrix[2][0] = (cos(angle_x) * sin(angle_y) * cos(angle_z)
+ sin(angle_x) * sin(angle_z));
matrix[2][1] = (-sin(angle_x) * cos(angle_z)
+ cos(angle_x) * sin(angle_y) * sin(angle_z));
matrix[2][2] = cos(angle_x) * cos(angle_y);
}
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