I got this n-dimensional point object:

template <class T, unsigned int dimension> class Obj {
protected:
    T coords[dimension];
    static const unsigned int size = dimension;
public:
    Obj() { };
    Obj(T def) { for (unsigned int i = 0; i < size; ++i) coords[i]=def; };
    Obj(const Obj& o) { for (unsigned int i = 0; i < size; ++i) coords[i] = o.coords[i]; }
    const Obj& operator= (const Obj& rhs) { if (this != &rhs) for (unsigned int i = 0; i < size; ++i) coords[i] = rhs.coords[i]; return *this; }


    virtual ~Obj() {  };
    T get (unsigned int id) { if (id >= size) throw std::out_of_range("out of range"); return coords[id]; }
    void set (unsigned int id, T t) { if (id >= size) throw std::out_of_range("out of range"); coords[id] = t; }

};

and a 3D point class which uses Obj as base class:

template <class U> class Point3DBase : public Obj<U,3> {
    typedef U type;

public:
    U &x, &y, &z;
public:
    Point3DBase() : x(Obj<U,3>::coords[0]), y(Obj<U,3>::coords[1]), z(Obj<U,3>::coords[2]) { };
    Point3DBase(U def) : Obj<U,3>(def), x(Obj<U,3>::coords[0]), y(Obj<U,3>::coords[1]), z(Obj<U,3>::coords[2]) { };
    Point3DBase(U x_, U y_, U z_) : x(Obj<U,3>::coords[0]), y(Obj<U,3>::coords[1]), z(Obj<U,3>::coords[2])  { x = x_; y = y_; z= z_; };
    Point3DBase(const Point3DBase& other) : x(Obj<U,3>::coords[0]), y(Obj<U,3>::coords[1]), z(Obj<U,3>::coords[2]) { x = other.x; y = other.y; z = other.z; }
// several operators ...
};

The operators, basically the ones for comparison, use the simple compare-the-member-object approach like:

virtual friend bool operator== (const Point3DBase<U> &lhs, const Point3DBase<U> rhs) { return (lhs.x ==  rhs.x && lhs.y == rhs.y && lhs.z == rhs.z); }

Then it occured to me that for the comparion of double values the simply equality approach is not very useful since double values should be compared with an error margin. What would be the best approach to introduce an error margin into the point? I thought about an epsDouble type as template parameter but I can't figure out how to achieve this.