private String getCacheKey(final Geopoint from, final Geopoint to) {
        return from.getLatitudeE6() + "," + from.getLongitudeE6() + "," + to.getLatitudeE6() + "," + to.getLongitudeE6();
    }
returns length in meters for the given route
main/src/main/java/cgeo/geocaching/maps/routing/RouteOptimizationHelper.java