GammaLib

The actual IRF interface has a lot of arguments for all observed (GInstDir, GEnergy, and GTime) and true (GSkyDir, GEnergy, and GTime) parameters. A more generic interface, allowing also for a more efficient implementation, is provided by regrouping the parameters into classes.

For the observed parameters, the GEvent class may be used.

For the true parameters, the GPhoton class may be used. This allows also easy extension to handle for example polarization.

The GResponse method should then have the following interfaces:

    virtual double      irf(const GEvent&       event,
                            const GPhoton&      photon,
                            const GObservation& obs) const = 0;
    virtual double      npred(const GPhoton&      photon,
                              const GObservation& obs) const = 0;

Additional, the following interfaces can be used for the GResponse virtual methods:

    virtual double irf(const GEvent&       event,
                       const GModelSky&    model,
                       const GEnergy&      srcEng,
                       const GTime&        srcTime,
                       const GObservation& obs) const;
    virtual double irf_ptsrc(const GEvent&            event,
                             const GModelPointSource& model,
                             const GEnergy&           srcEng,
                             const GTime&             srcTime,
                             const GObservation&   obs) const;
    virtual double irf_extended(const GEvent&               event,
                                const GModelExtendedSource& model,
                                const GEnergy&              srcEng,
                                const GTime&                srcTime,
                                const GObservation&         obs) const;
    virtual double irf_diffuse(const GEvent&              event,
                               const GModelDiffuseSource& model,
                               const GEnergy&             srcEng,
                               const GTime&               srcTime,
                               const GObservation&        obs) const;
    virtual double npred(const GModelSky&    model,
                         const GEnergy&      srcEng,
                         const GTime&        srcTime,
                         const GObservation& obs) const;
    virtual double npred_ptsrc(const GModelPointSource& model,
                               const GEnergy&           srcEng,
                               const GTime&             srcTime,
                               const GObservation&      obs) const;
    virtual double npred_extended(const GModelExtendedSource& model,
                                  const GEnergy&              srcEng,
                                  const GTime&                srcTime,
                                  const GObservation&         obs) const;
    virtual double npred_diffuse(const GModelDiffuseSource& model,
                                 const GEnergy&             srcEng,
                                 const GTime&               srcTime,
                                 const GObservation&        obs) const;

It remains to be seen whether the remaining pairs of GEnergy and GTime should be combined in a GPhoton object where the spatial direction is ignored. Alternative, a new class GSource could be introduced that has (GModelSky, GEnergy and GTime) as members. GSource could be even a base class that implements GPointSource, GDiffuseSource, and GExtendedSource