wind_overlap.c

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#include <grass/gis.h>


int G_window_overlap(const struct Cell_head *window,
                     double N, double S, double E, double W)
{
    if (window->north <= S)
        return 0;
    if (window->south >= N)
        return 0;

    if (window->proj == PROJECTION_LL) {
        while (E < window->west) {
            E += 360.0;
            W += 360.0;
        }
        while (W > window->east) {
            E -= 360.0;
            W -= 360.0;
        }
    }

    if (window->east <= W)
        return 0;
    if (window->west >= E)
        return 0;

    return 1;
}


double G_window_percentage_overlap(const struct Cell_head *window,
                                   double N, double S, double E, double W)
{
    double V, H;
    double n, s, e, w;
    double shift;

    /* vertical height of the box that overlaps the window */
    if ((n = window->north) > N)
        n = N;
    if ((s = window->south) < S)
        s = S;
    V = n - s;

    if (V <= 0.0)
        return 0.0;

    /* global wrap-around, part 1 */
    if (window->proj == PROJECTION_LL) {
        shift = 0.0;
        while (E + shift > window->east)
            shift -= 360.0;
        while (E + shift < window->west)
            shift += 360.0;
        E += shift;
        W += shift;
    }

    /* horizontal width of the box that overlaps the window */
    if ((e = window->east) > E)
        e = E;
    if ((w = window->west) < W)
        w = W;
    H = e - w;
    if (H <= 0.0)
        return 0.0;

    /* global wrap-around, part 2 */
    if (window->proj == PROJECTION_LL) {
        shift = 0.0;
        while (W + shift < window->west)
            shift += 360.0;
        while (W + shift > window->east)
            shift -= 360.0;
        if (shift) {
            E += shift;
            W += shift;
            if ((e = window->east) > E)
                e = E;
            if ((w = window->west) < W)
                w = W;
            H += e - w;
        }
    }

    return (H * V) / ((N - S) * (E - W));
}