[Insight-users] Using itk::hash_table

[motes motes]

I would like to use a itk::hash_table to store my own objects (for
spatial hashing).

For each index in the hash_table a list of objects should be stored
based on a hash value (pretty much the definition of a hash-table).

I would like to compute this hash value based on the location of each
of the objects which contains a 3D vector corresponding to its
location in space.

Something like (the below is python code use as an example from the
website: http://entitycrisis.blogspot.com/2007/11/spatial-hashing.html):

    def key(self, point):
        cell_size = self.cell_size
        return (
            int((floor(point[0]/cell_size))*cell_size),
            int((floor(point[1]/cell_size))*cell_size),
            int((floor(point[2]/cell_size))*cell_size)
        )


So if I do:


void eval(VectorType v) {
 std::vector<MyObj> chain =  hash_map.get(v);

}

I should get all those elements that hash to the value based on the "key" v.



I have done the following:


  typedef itk::Vector<double, Dimension>
                                           VectorType;
  typedef MyPoint<VectorType>
                                             MyPointType;
  typedef std::pair<MyPointType,int>
                                           ValueType;
  typedef unsigned long
                                                  IdentifierType;
  typedef itk::hash_map<MyPointType, IdentifierType,
MyHashFunction<MyPointType > >   HashMap;

  HashMap m_HashTable;

  MyPointType cp0;
  VectorType vec0;
  ValueType val0;
  val0.first = cp0;
  val0.second = 12;


In MyPoint I have implemented the following operators:

    bool operator==(const MyPoint & mp) const {
      return !(*this == mp);
    }

    int operator ()(MyPoint  & mp) {
      // hm what todo here? Return cell size?
      return 10;
    }







I have created the following hash functor:

  template< class TInput >
  class MyHashFunction
  {
  public:

    typedef MyHashFunction Self;
    typedef TInput InputType;
    typedef InputType::VectorType    VectorType;

    unsigned int operator()( const InputType& key ) const;

  };

  template< class TInput >
  inline unsigned int
  MyHashFunction< TInput >
  ::operator()( const InputType& key ) const
  {

     VectorType position = key.getPosition();
    double cellSize = key.getCellSize();

    // Do something like the above pythion scripts....
    return hash;

  }


But I am not sure what I should use the operator "()" for  and what
the:  "IdentifierType" represents.

Another think. I need to get all elements associated with the key 'k'.
By all elements I mean the "chain/list" connected to the index
returned by the hash_function. Is that possible with the
itk::hash__table or should I look into the std::map containing lists
instead?