- double x1() { return property_x1(); }
- double y1() { return property_y1(); }
- double x2() { return property_x2(); }
- double y2() { return property_y2(); }
+ double x1() const { return property_x1(); }
+ double y1() const { return property_y1(); }
+ double x2() const { return property_x2(); }
+ double y2() const { return property_y2(); }