gbox_angular_width()

double gbox_angular_width

(

const GBOX *

gbox

)

Returns the angular width (longitudinal span) of the box in radians.

Definition at line 215 of file lwgeodetic.c.

{
        double d[6];
        int i, j;
        POINT3D pt[3];
        double maxangle;
        double magnitude;
 
        /* Take a copy of the box corners so we can treat them as a list */
        /* Elements are xmin, xmax, ymin, ymax, zmin, zmax */
        memcpy(d, &(gbox->xmin), 6*sizeof(double));
 
        /* Start with the bottom corner */
        pt[0].x = gbox->xmin;
        pt[0].y = gbox->ymin;
        magnitude = sqrt(pt[0].x*pt[0].x + pt[0].y*pt[0].y);
        pt[0].x /= magnitude;
        pt[0].y /= magnitude;
 
        /* Generate all 8 corner vectors of the box */
        /* Find the vector furthest from our seed vector */
        for ( j = 0; j < 2; j++ )
        {
                maxangle = -1 * FLT_MAX;
                for ( i = 0; i < 4; i++ )
                {
                        double angle, dotprod;
                        POINT3D pt_n;
 
                        pt_n.x = d[i / 2];
                        pt_n.y = d[2 + (i % 2)];
                        magnitude = sqrt(pt_n.x*pt_n.x + pt_n.y*pt_n.y);
                        pt_n.x /= magnitude;
                        pt_n.y /= magnitude;
                        pt_n.z = 0.0;
 
                        dotprod = pt_n.x*pt[j].x + pt_n.y*pt[j].y;
                        angle = acos(dotprod > 1.0 ? 1.0 : dotprod);
                        if ( angle > maxangle )
                        {
                                pt[j+1] = pt_n;
                                maxangle = angle;
                        }
                }
        }
 
        /* Return the distance between the two furthest vectors */
        return maxangle;
}

References POINT3D::x, GBOX::xmin, POINT3D::y, GBOX::ymin, and POINT3D::z.

Referenced by geography_bestsrid(), and test_gbox_utils().

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