távolság

[Szima Gábor]

On Fri, 15 Oct 2004, zulu wrote:

> Nemtom mekkora a probléma, de nem találok sehol képletet gömbfelületen  2 pont közötti - a gömbfelületen ívelt - távolság
> meg6ározására. Adva van 2 pont lon/lat koordináta fok/perc/mpercben. Tud valaki megoldást?

Rohogni fogsz:

postgresql/contrib/earthdistance/earthdistance.c:

const double    EARTH_RADIUS = 3958.747716;
const double    TWO_PI = 2.0 * M_PI;

double     *geo_distance(Point *pt1, Point *pt2);

/******************************************************
 *
 * degtorad - convert degrees to radians
 *
 * arg: double, angle in degrees
 *
 * returns: double, same angle in radians
 ******************************************************/

static double
degtorad(double degrees)
{
        return (degrees / 360.0) * TWO_PI;
}



/******************************************************
 *
 * geo_distance - distance between points
 *
 * args:
 *       a pair of points - for each point,
 *         x-coordinate is longitude in degrees west of Greenwich
 *         y-coordinate is latitude in degrees above equator
 *
 * returns: double
 *       distance between the points in miles on earth's surface
 ******************************************************/

double *
geo_distance(Point *pt1, Point *pt2)
{

        double          long1,
                                lat1,
                                long2,
                                lat2;
        double          longdiff;
        double          sino;
        double     *resultp = palloc(sizeof(double));

        /* convert degrees to radians */

        long1 = degtorad(pt1->x);
        lat1 = degtorad(pt1->y);

        long2 = degtorad(pt2->x);
        lat2 = degtorad(pt2->y);

        /* compute difference in longitudes - want < 180 degrees */
        longdiff = fabs(long1 - long2);
        if (longdiff > M_PI)
                longdiff = TWO_PI - longdiff;

        sino = sqrt(sin(fabs(lat1-lat2)/2.)*sin(fabs(lat1-lat2)/2.) +
                cos(lat1) * cos(lat2) * sin(longdiff/2.)*sin(longdiff/2.));
        if (sino > 1.) sino = 1.;
        *resultp = 2. * EARTH_RADIUS * asin(sino);

        return resultp;
}




								-Sygma