Feat: implement spreading loss for PPE

Implements spreading loss by function (23) in 'A Uniform Geometrical Theory of Diffraction... Kouyoumijian 1974'.

include/ITAPropagationModels/PropagationParameterEngine/PropagationModules/SpreadingLossModules/SpreadingLoss.h

+#ifndef INCLUDE_WATCHER_PP_PROPAGATION_DELAY
+#define INCLUDE_WATCHER_PP_PROPAGATION_DELAY
+
+
+#include <ITAPropagationModels/Definitions.h>
+#include <ITAPropagationModels/PropagationParameterEngine/AuUnits.h>
+#include <ITAPropagationModels/PropagationParameterEngine/PropagationModules/BaseModule.h>
+#include <ITAPropagationModels/PropagationParameterEngine/PropagationParameters/SingleData.h>
+#include <ITAPropagationModels/PropagationParameterEngine/UtilsPPE.h>
+#include <memory>
+#include <propagation_path_list/propagation_path_list.hpp>
+#include <string>
+
+namespace ITAPropagationModels
+{
+	namespace PPE
+	{
+		namespace PropModules
+		{
+			///
+			/// \brief Module to compute the spreading loss for a given propagation path list.
+			///
+			/// The calculation is based on the paper "A uniform geometrical theory of diffraction for an edge in a perfectly conducting surface" by R. G. Kouyoumjian and
+			/// P. H. Pathak, Equation (23).
+			///
+			class ITA_PROPAGATION_MODELS_API CSpreadingLoss : public CBaseModules
+			{
+			public:
+				CSpreadingLoss( );
+				~CSpreadingLoss( ) = default;
+
+				PPLResults compute( const propagation_path_list::PropagationPathList& ppl ) override;
+
+				EModuleIdentifier get_identifier( ) const override { return EModuleIdentifier::SPREADING_LOSS; };
+
+			private:
+				///
+				/// \brief Compute the length of each section of a propagation path.
+				///
+				/// In this context, a section is defined as the distance between diffraction anchors.
+				/// This is done, because the spreading loss is calculated differently for spherical and cylindrical waves.
+				/// Considering spherical waves emanating from a point source, spherical spreading loss needs to be calculated when a reflection or the receiver is
+				/// encountered.
+				/// When a diffraction is encountered, the diffracted wave is emanating from a virtual line source along the edge of the diffracting object.
+				/// Therefore, cylindrical spreading loss needs to be calculated following a diffraction.
+				/// \param ppl Propagation path list to compute the section lengths for.
+				/// \return A map containing the path identifier as key and a vector of section lengths as value.
+				///
+				std::unordered_map<std::string, std::vector<decltype( au::meters( float( ) ) )>> compute_sound_path_section_length(
+				    const propagation_path_list::PropagationPathList& ppl );
+
+				///
+				/// \brief Compute the spreading loss for a given propagation path list.
+				///
+				/// This method does the actual computation of the spreading loss for a given propagation path list.
+				/// \param ppl Propagation path list to compute the spreading loss for.
+				/// \return PPLResults containing the spreading loss for each path.
+				///
+				PPLResults compute_spreading_loss_list( const propagation_path_list::PropagationPathList& ppl );
+
+				bool m_spherical_only = false;
+			};
+
+
+		} // namespace PropModules
+	} // namespace PPE
+} // namespace ITAPropagationModels
+
+
+#endif // !INCLUDE_WATCHER_PP_PROPAGATION_DELAY