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Norman Vine optimizations.

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curt 2001-06-12 21:44:03 +00:00
parent 887ffd102f
commit 48a219473e
1 changed files with 75 additions and 0 deletions
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75
simgear/math/polar3d.hxx
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@ -122,6 +122,80 @@ inline Point3D calc_gc_lon_lat( const Point3D& orig, double course,
}
/**
* Calculate course/dist given two spherical points.
* @param start starting point
* @param dest ending point
* @param course resulting course
* @param dist resulting distance
*/
inline void calc_gc_course_dist( const Point3D& start, const Point3D& dest,
double *course, double *dist )
{
// d = 2*asin(sqrt((sin((lat1-lat2)/2))^2 +
// cos(lat1)*cos(lat2)*(sin((lon1-lon2)/2))^2))
double cos_start_y = cos( start.y() );
volatile double tmp1 = sin( (start.y() - dest.y()) * 0.5 );
volatile double tmp2 = sin( (start.x() - dest.x()) * 0.5 );
double d = 2.0 * asin( sqrt( tmp1 * tmp1 +
cos_start_y * cos(dest.y()) * tmp2 * tmp2));
*dist = d * SG_RAD_TO_NM * SG_NM_TO_METER;
// We obtain the initial course, tc1, (at point 1) from point 1 to
// point 2 by the following. The formula fails if the initial
// point is a pole. We can special case this with:
//
// IF (cos(lat1) < EPS) // EPS a small number ~ machine precision
// IF (lat1 > 0)
// tc1= pi // starting from N pole
// ELSE
// tc1= 0 // starting from S pole
// ENDIF
// ENDIF
//
// For starting points other than the poles:
//
// IF sin(lon2-lon1)<0
// tc1=acos((sin(lat2)-sin(lat1)*cos(d))/(sin(d)*cos(lat1)))
// ELSE
// tc1=2*pi-acos((sin(lat2)-sin(lat1)*cos(d))/(sin(d)*cos(lat1)))
// ENDIF
// if ( cos(start.y()) < SG_EPSILON ) {
// doing it this way saves a transcendental call
double sin_start_y = sin( start.y() );
if ( fabs(1.0-sin_start_y) < SG_EPSILON ) {
// EPS a small number ~ machine precision
if ( start.y() > 0 ) {
*course = SGD_PI; // starting from N pole
} else {
*course = 0; // starting from S pole
}
} else {
// For starting points other than the poles:
// double tmp3 = sin(d)*cos_start_y);
// double tmp4 = sin(dest.y())-sin(start.y())*cos(d);
// double tmp5 = acos(tmp4/tmp3);
// Doing this way gaurentees that the temps are
// not stored into memory
double tmp5 = acos( (sin(dest.y()) - sin_start_y * cos(d)) /
(sin(d) * cos_start_y) );
// if ( sin( dest.x() - start.x() ) < 0 ) {
// the sin of the negative angle is just the opposite sign
// of the sin of the angle so tmp2 will have the opposite
// sign of sin( dest.x() - start.x() )
if ( tmp2 >= 0 ) {
*course = tmp5;
} else {
*course = 2 * SGD_PI - tmp5;
}
}
}
#if 0
/**
* Calculate course/dist given two spherical points.
* @param start starting point
@ -183,5 +257,6 @@ inline void calc_gc_course_dist( const Point3D& start, const Point3D& dest,
*course = tc1;
*dist = d * SG_RAD_TO_NM * SG_NM_TO_METER;
}
#endif // 0
#endif // _POLAR3D_HXX