daylength_calculator.h

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#ifndef DAYLENGTH_CALCULATOR_H
#define DAYLENGTH_CALCULATOR_H
 
#include <cmath>      // cos, sin
#include <algorithm>  // min, max
#include "../framework/module.h"
#include "../framework/state_map.h"
#include "../framework/constants.h"  //pi
 
namespace standardBML
{
 
class daylength_calculator : public direct_module
{
   public:
    daylength_calculator(
        state_map const& input_quantities,
        state_map* output_quantities)
        : direct_module{},
 
          // Get references to input quantities
          lat{get_input(input_quantities, "lat")},
          solar_dec{get_input(input_quantities, "solar_dec")},
          p{get_input(input_quantities, "sunrise_sunset_elevation")},
          // Get pointers to output quantities
          daylength{get_op(output_quantities, "day_length")}
 
    {
    }
    static string_vector get_inputs();
    static string_vector get_outputs();
    static std::string get_name() { return "daylength_calculator"; }
 
   private:
    // References to input quantities
    const double& lat;
    const double& solar_dec;
    const double& p;
 
    // Pointers to output quantities
    double* daylength;
    // Main operation
    void do_operation() const;
};
 
string_vector daylength_calculator::get_inputs()
{
    return {
        "lat",                      // degrees
        "solar_dec",                // degrees
        "sunrise_sunset_elevation"  // degrees
    };
}
 
string_vector daylength_calculator::get_outputs()
{
    return {
        "day_length"  // hr
    };
}
 
void daylength_calculator::do_operation() const
{
    using math_constants::pi;
    constexpr double to_rad = pi / 180;                     // radian / degree
    double offset = std::sin(p * to_rad);                   // dimensionless
    double lam = lat * to_rad;                              // radians
    double phi = solar_dec * to_rad;                        // radians
    double num = offset + std::sin(lam) * std::sin(phi);    // dimensionaless
    double denom = std::cos(lam) * std::cos(phi);           // dimensionless
    double u = std::max(std::min(num / denom, 1.0), -1.0);  // dimensionless
    double D = 24 - 24 / pi * std::acos(u);                 // hours
    update(daylength, D);                                   // hours
}
 
}  // namespace standardBML
 
#endif