is_clockwise()

static int is_clockwise ( int  num_points, double *  x, double *  y, double *  z  )

static

Definition at line 490 of file pgsql2shp-core.c.

References area(), free(), and malloc().

Referenced by create_multipolygon(), create_polygon(), and ST_IsPolygonCW().

{
        int i;
        double x_change,y_change,area;
        double *x_new, *y_new; /* the points, translated to the origin
                                                        * for safer accuracy */

        x_new = (double *)malloc(sizeof(double) * num_points);
        y_new = (double *)malloc(sizeof(double) * num_points);
        area=0.0;
        x_change = x[0];
        y_change = y[0];

        for (i=0; i < num_points ; i++)
        {
                x_new[i] = x[i] - x_change;
                y_new[i] = y[i] - y_change;
        }

        for (i=0; i < num_points - 1; i++)
        {
                /* calculate the area    */
                area += (x[i] * y[i+1]) - (y[i] * x[i+1]);
        }
        if (area > 0 )
        {
                free(x_new);
                free(y_new);
                return 0; /*counter-clockwise */
        }
        else
        {
                free(x_new);
                free(y_new);
                return 1; /*clockwise */
        }
}

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