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#ifndef PCL_INTENSITY_GRADIENT_H_
#define PCL_INTENSITY_GRADIENT_H_

#include <pcl/features/feature.h>
#include <pcl/common/intensity.h>

namespace pcl
{
  /** \brief IntensityGradientEstimation estimates the intensity gradient for a point cloud that contains position
    * and intensity values.  The intensity gradient at a given point will be a vector orthogonal to the surface
    * normal and pointing in the direction of the greatest increase in local intensity; the vector's magnitude
    * indicates the rate of intensity change.
    * \author Michael Dixon
    * \ingroup features
    */
  template <typename PointInT, typename PointNT, typename PointOutT, typename IntensitySelectorT = pcl::common::IntensityFieldAccessor<PointInT> >
  class IntensityGradientEstimation : public FeatureFromNormals<PointInT, PointNT, PointOutT>
  {
    public:
      typedef boost::shared_ptr<IntensityGradientEstimation<PointInT, PointNT, PointOutT, IntensitySelectorT> > Ptr;
      typedef boost::shared_ptr<const IntensityGradientEstimation<PointInT, PointNT, PointOutT, IntensitySelectorT> > ConstPtr;
      using Feature<PointInT, PointOutT>::feature_name_;
      using Feature<PointInT, PointOutT>::getClassName;
      using Feature<PointInT, PointOutT>::indices_;
      using Feature<PointInT, PointOutT>::surface_;
      using Feature<PointInT, PointOutT>::k_;
      using Feature<PointInT, PointOutT>::search_parameter_;
      using FeatureFromNormals<PointInT, PointNT, PointOutT>::normals_;

      typedef typename Feature<PointInT, PointOutT>::PointCloudOut PointCloudOut;

      /** \brief Empty constructor. */
      IntensityGradientEstimation () : intensity_ (), threads_ (0)
      {
        feature_name_ = "IntensityGradientEstimation";
      };

      /** \brief Initialize the scheduler and set the number of threads to use.
        * \param nr_threads the number of hardware threads to use (0 sets the value back to automatic)
        */
      inline void
      setNumberOfThreads (unsigned int nr_threads = 0) { threads_ = nr_threads; }

    protected:
      /** \brief Estimate the intensity gradients for a set of points given in <setInputCloud (), setIndices ()> using
        *  the surface in setSearchSurface () and the spatial locator in setSearchMethod ().
        *  \param output the resultant point cloud that contains the intensity gradient vectors
        */
      void
      computeFeature (PointCloudOut &output);

      /** \brief Estimate the intensity gradient around a given point based on its spatial neighborhood of points
        * \param cloud a point cloud dataset containing XYZI coordinates (Cartesian coordinates + intensity)
        * \param indices the indices of the neighoring points in the dataset
        * \param point the 3D Cartesian coordinates of the point at which to estimate the gradient
        * \param mean_intensity
        * \param normal the 3D surface normal of the given point
        * \param gradient the resultant 3D gradient vector
        */
      void
      computePointIntensityGradient (const pcl::PointCloud<PointInT> &cloud,
                                     const std::vector<int> &indices,
                                     const Eigen::Vector3f &point, 
                                     float mean_intensity, 
                                     const Eigen::Vector3f &normal,
                                     Eigen::Vector3f &gradient);

    protected:
      ///intensity field accessor structure
      IntensitySelectorT intensity_;
      ///number of threads to be used, default 0 (auto)
      unsigned int threads_;
  };
}

#ifdef PCL_NO_PRECOMPILE
#include <pcl/features/impl/intensity_gradient.hpp>
#endif

#endif // #ifndef PCL_INTENSITY_GRADIENT_H_
