spheroid_striparea()

static double spheroid_striparea ( const GEOGRAPHIC_POINT *  a, const GEOGRAPHIC_POINT *  b, double  latitude_min, const SPHEROID *  spheroid  )

static

This function doesn't work for edges crossing the dateline or in the southern hemisphere.

Points are pre-conditioned in ptarray_area_spheroid.

Definition at line 460 of file lwspheroid.c.

{
        GEOGRAPHIC_POINT A, B, mL, nR;
        double deltaLng, baseArea, topArea;
        double bE, tE, ratio, sign;
 
        A = *a;
        B = *b;
 
        mL.lat = latitude_min;
        mL.lon = FP_MIN(A.lon, B.lon);
        nR.lat = FP_MIN(A.lat, B.lat);
        nR.lon = FP_MAX(A.lon, B.lon);
        LWDEBUGF(4, "mL (%.12g %.12g)", mL.lat, mL.lon);
        LWDEBUGF(4, "nR (%.12g %.12g)", nR.lat, nR.lon);
        baseArea = spheroid_boundingbox_area(&mL, &nR, spheroid);
        LWDEBUGF(4, "baseArea %.12g", baseArea);
 
        mL.lat = FP_MIN(A.lat, B.lat);
        mL.lon = FP_MIN(A.lon, B.lon);
        nR.lat = FP_MAX(A.lat, B.lat);
        nR.lon = FP_MAX(A.lon, B.lon);
        LWDEBUGF(4, "mL (%.12g %.12g)", mL.lat, mL.lon);
        LWDEBUGF(4, "nR (%.12g %.12g)", nR.lat, nR.lon);
        topArea = spheroid_boundingbox_area(&mL, &nR, spheroid);
        LWDEBUGF(4, "topArea %.12g", topArea);
 
        deltaLng = B.lon - A.lon;
        LWDEBUGF(4, "deltaLng %.12g", deltaLng);
        bE = spheroid_parallel_arc_length(A.lat, deltaLng, spheroid);
        tE = spheroid_parallel_arc_length(B.lat, deltaLng, spheroid);
        LWDEBUGF(4, "bE %.12g", bE);
        LWDEBUGF(4, "tE %.12g", tE);
 
        ratio = (bE + tE)/tE;
        sign = SIGNUM(B.lon - A.lon);
        return (baseArea + topArea / ratio) * sign;
}

References FP_MAX, FP_MIN, GEOGRAPHIC_POINT::lat, GEOGRAPHIC_POINT::lon, LWDEBUGF, SIGNUM, spheroid_boundingbox_area(), and spheroid_parallel_arc_length().

Referenced by ptarray_area_spheroid().

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