geohash_point()

lwvarlena_t* geohash_point	(	double	longitude,
		double	latitude,
		int	precision
	)

Definition at line 598 of file lwalgorithm.c.

{
        int is_even=1, i=0;
        double lat[2], lon[2], mid;
        char bits[] = {16,8,4,2,1};
        int bit=0, ch=0;
        lwvarlena_t *v = lwalloc(precision + LWVARHDRSZ);
        LWSIZE_SET(v->size, precision + LWVARHDRSZ);
        char *geohash = v->data;
 
        lat[0] = -90.0;
        lat[1] = 90.0;
        lon[0] = -180.0;
        lon[1] = 180.0;
 
        while (i < precision)
        {
                if (is_even)
                {
                        mid = (lon[0] + lon[1]) / 2;
                        if (longitude >= mid)
                        {
                                ch |= bits[bit];
                                lon[0] = mid;
                        }
                        else
                        {
                                lon[1] = mid;
                        }
                }
                else
                {
                        mid = (lat[0] + lat[1]) / 2;
                        if (latitude >= mid)
                        {
                                ch |= bits[bit];
                                lat[0] = mid;
                        }
                        else
                        {
                                lat[1] = mid;
                        }
                }
 
                is_even = !is_even;
                if (bit < 4)
                {
                        bit++;
                }
                else
                {
                        geohash[i++] = base32[ch];
                        bit = 0;
                        ch = 0;
                }
        }
 
        return v;
}

References base32, lwvarlena_t::data, lwalloc(), LWSIZE_SET, LWVARHDRSZ, precision, and lwvarlena_t::size.

Referenced by lwgeom_geohash(), and test_geohash_point().

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