C++ overriding functions in classes set specifically for partial template specialization

I am writing a point cloud class with several features. I wanted to implement some specific function for only 3 dimensional point clouds. Therefore I implemented the general class hierarchy in the following way in which I partially specialize one of the template arguments for the point cloud (using Eigen as the linear algebra library):

template <typename T, unsigned int DIM>
class PointCloudBase {
   public:
    using Vector = Eigen::Matrix<T, DIM, 1>;
    using Hyperplane = Eigen::Hyperplane<T, DIM>;
    using MatrixDIM = Eigen::Matrix<T, DIM, DIM>;
    using AlignedBox = Eigen::AlignedBox<T, DIM>;

    bool convexHullIntersects(const AlignedBox& box) const {
       // generic implementation for this function
    }

    // more stuff here

};


template<typename T, unsigned int DIM>
class PointCloud : public PointCloudBase<T, DIM> {

};


template<typename T>
class PointCloud<T, 3U> : public PointCloudBase<T, 3U> {
  public:

    using typename PointCloudBase<T, 3U>::AlignedBox;
    using typename PointCloudBase<T, 3U>::Vector;
    bool convexHullIntersects(const AlignedBox& box) const override {
      // implementation specific to DIM = 3U
    }
};

However when I try to instantiate the class as PointCloud<double, 3U> pc;, I get the following error that complains that convexHullIntersection is not overriding anything:

error: ‘bool PointCloud<T, 3>::convexHullIntersects(const typename PointCloudBase<T, 3>::AlignedBox&) const [with T = double; typename PointCloudBase<T, 3>::AlignedBox = Eigen::AlignedBox<double, 3>]’ marked ‘override’, but does not override

What can be the problem here?

Thanks!