code: public void getFeature3D( int feature , Point4D_F64 out ) {
  		out.x = X.get(0,feature);
  		out.y = X.get(1,feature);
  		out.z = X.get(2,feature);
  		out.w = X.get(3,feature);
  	}
docs: Returns location of 3D feature for a view
  @param feature Index of feature to retrieve
  @param out (Output) Storage for 3D feature. homogenous coordinates