/***********************************************************************//**
* @brief Evaluate function
*
* @param[in] event Observed event.
* @param[in] obs Observation.
* @return Function value.
*
* @exception GException::invalid_argument
* Specified observation is not of the expected type.
*
* @todo Make sure that DETX and DETY are always set in GCTAInstDir.
***************************************************************************/
double GCTAModelIrfBackground::eval(const GEvent& event,
const GObservation& obs) const
{
// Get pointer on CTA observation
const GCTAObservation* cta = dynamic_cast<const GCTAObservation*>(&obs);
if (cta == NULL) {
std::string msg = "Specified observation is not a CTA observation.\n" +
obs.print();
throw GException::invalid_argument(G_EVAL, msg);
}
// Get pointer on CTA IRF response
const GCTAResponseIrf* rsp = dynamic_cast<const GCTAResponseIrf*>(cta->response());
if (rsp == NULL) {
std::string msg = "Specified observation does not contain an IRF response.\n" +
obs.print();
throw GException::invalid_argument(G_EVAL, msg);
}
// Retrieve pointer to CTA background
const GCTABackground* bgd = rsp->background();
if (bgd == NULL) {
std::string msg = "Specified observation contains no background"
" information.\n" + obs.print();
throw GException::invalid_argument(G_EVAL, msg);
}
// Extract CTA instrument direction from event
const GCTAInstDir* dir = dynamic_cast<const GCTAInstDir*>(&(event.dir()));
if (dir == NULL) {
std::string msg = "No CTA instrument direction found in event.";
throw GException::invalid_argument(G_EVAL, msg);
}
// Set DETX and DETY in instrument direction
GCTAInstDir inst_dir = cta->pointing().instdir(dir->dir());
// Evaluate function
double logE = event.energy().log10TeV();
double spat = (*bgd)(logE, inst_dir.detx(), inst_dir.dety());
double spec = (spectral() != NULL)
? spectral()->eval(event.energy(), event.time()) : 1.0;
double temp = (temporal() != NULL)
? temporal()->eval(event.time()) : 1.0;
// Compute value
double value = spat * spec * temp;
// Apply deadtime correction
value *= obs.deadc(event.time());
// Return value
return value;
}
/***********************************************************************//**
* @brief Evaluate function
*
* @param[in] event Observed event.
* @param[in] obs Observation.
* @return Function value.
*
* @exception GException::invalid_argument
* No CTA instrument direction found in event.
*
* Evaluates tha CTA background model which is a factorization of a
* spatial, spectral and temporal model component. This method also applies
* a deadtime correction factor, so that the normalization of the model is
* a real rate (counts/exposure time).
*
* @todo Add bookkeeping of last value and evaluate only if argument
* changed
***************************************************************************/
double GCTAModelBackground::eval(const GEvent& event,
const GObservation& obs) const
{
// Get pointer on CTA observation
const GCTAObservation* ctaobs = dynamic_cast<const GCTAObservation*>(&obs);
if (ctaobs == NULL) {
std::string msg = "Specified observation is not a CTA observation.\n" +
obs.print();
throw GException::invalid_argument(G_EVAL, msg);
}
// Extract CTA instrument direction
const GCTAInstDir* dir = dynamic_cast<const GCTAInstDir*>(&(event.dir()));
if (dir == NULL) {
std::string msg = "No CTA instrument direction found in event.";
throw GException::invalid_argument(G_EVAL, msg);
}
// Create a Photon from the event.
// We need the GPhoton to evaluate the spatial model.
// For the background, GEvent and GPhoton are identical
// since the IRFs are not folded in
GPhoton photon(dir->dir(), event.energy(), event.time());
// Evaluate function and gradients
double spat = (spatial() != NULL)
? spatial()->eval(photon) : 1.0;
double spec = (spectral() != NULL)
? spectral()->eval(event.energy(), event.time()) : 1.0;
double temp = (temporal() != NULL)
? temporal()->eval(event.time()) : 1.0;
// Compute value
double value = spat * spec * temp;
// Apply deadtime correction
value *= obs.deadc(event.time());
// Return
return value;
}
/***********************************************************************//**
* @brief Return spatially integrated background model
*
* @param[in] obsEng Measured event energy.
* @param[in] obsTime Measured event time.
* @param[in] obs Observation.
* @return Spatially integrated model.
*
* @exception GException::invalid_argument
* The specified observation is not a CTA observation.
*
* Spatially integrates the cube background model for a given measured event
* energy and event time. This method also applies a deadtime correction
* factor, so that the normalization of the model is a real rate
* (counts/MeV/s).
***************************************************************************/
double GCTAModelCubeBackground::npred(const GEnergy& obsEng,
const GTime& obsTime,
const GObservation& obs) const
{
// Initialise result
double npred = 0.0;
bool has_npred = false;
// Build unique identifier
std::string id = obs.instrument() + "::" + obs.id();
// Check if Npred value is already in cache
#if defined(G_USE_NPRED_CACHE)
if (!m_npred_names.empty()) {
// Search for unique identifier, and if found, recover Npred value
// and break
for (int i = 0; i < m_npred_names.size(); ++i) {
if (m_npred_names[i] == id && m_npred_energies[i] == obsEng) {
npred = m_npred_values[i];
has_npred = true;
#if defined(G_DEBUG_NPRED)
std::cout << "GCTAModelCubeBackground::npred:";
std::cout << " cache=" << i;
std::cout << " npred=" << npred << std::endl;
#endif
break;
}
}
} // endif: there were values in the Npred cache
#endif
// Continue only if no Npred cache value has been found
if (!has_npred) {
// Evaluate only if model is valid
if (valid_model()) {
// Get pointer on CTA observation
const GCTAObservation* cta = dynamic_cast<const GCTAObservation*>(&obs);
if (cta == NULL) {
std::string msg = "Specified observation is not a CTA"
" observation.\n" + obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
// Get pointer on CTA cube response
const GCTAResponseCube* rsp = dynamic_cast<const GCTAResponseCube*>(cta->response());
if (rsp == NULL) {
std::string msg = "Specified observation does not contain"
" a cube response.\n" + obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
// Get log10 of energy in TeV
double logE = obsEng.log10TeV();
// Retrieve CTA background
const GCTACubeBackground bgd = rsp->background();
// Integrate the background map at a certain energy
npred = bgd.integral(logE);
// Store result in Npred cache
#if defined(G_USE_NPRED_CACHE)
m_npred_names.push_back(id);
m_npred_energies.push_back(obsEng);
m_npred_times.push_back(obsTime);
m_npred_values.push_back(npred);
#endif
// Debug: Check for NaN
#if defined(G_NAN_CHECK)
if (gammalib::is_notanumber(npred) || gammalib::is_infinite(npred)) {
std::string origin = "GCTAModelCubeBackground::npred";
std::string message = " NaN/Inf encountered (npred=" +
gammalib::str(npred) + ")";
gammalib::warning(origin, message);
}
#endif
} // endif: model was valid
} // endif: Npred computation required
// Multiply in spectral and temporal components
npred *= spectral()->eval(obsEng, obsTime);
npred *= temporal()->eval(obsTime);
// Apply deadtime correction
npred *= obs.deadc(obsTime);
// Return Npred
return npred;
}
/***********************************************************************//**
* @brief Return spatially integrated data model
*
* @param[in] obsEng Measured event energy.
* @param[in] obsTime Measured event time.
* @param[in] obs Observation.
* @return Spatially integrated model.
*
* @exception GException::invalid_argument
* No CTA event list found in observation.
* No CTA pointing found in observation.
*
* Spatially integrates the data model for a given measured event energy and
* event time. This method also applies a deadtime correction factor, so that
* the normalization of the model is a real rate (counts/exposure time).
***************************************************************************/
double GCTAModelBackground::npred(const GEnergy& obsEng,
const GTime& obsTime,
const GObservation& obs) const
{
// Initialise result
double npred = 0.0;
bool has_npred = false;
// Build unique identifier
std::string id = obs.instrument() + "::" + obs.id();
// Check if Npred value is already in cache
#if defined(G_USE_NPRED_CACHE)
if (!m_npred_names.empty()) {
// Search for unique identifier, and if found, recover Npred value
// and break
for (int i = 0; i < m_npred_names.size(); ++i) {
if (m_npred_names[i] == id && m_npred_energies[i] == obsEng) {
npred = m_npred_values[i];
has_npred = true;
#if defined(G_DEBUG_NPRED)
std::cout << "GCTAModelBackground::npred:";
std::cout << " cache=" << i;
std::cout << " npred=" << npred << std::endl;
#endif
break;
}
}
} // endif: there were values in the Npred cache
#endif
// Continue only if no Npred cache value was found
if (!has_npred) {
// Evaluate only if model is valid
if (valid_model()) {
// Get CTA event list
const GCTAEventList* events = dynamic_cast<const GCTAEventList*>(obs.events());
if (events == NULL) {
std::string msg = "No CTA event list found in observation.\n" +
obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
#if !defined(G_NPRED_AROUND_ROI)
// Get CTA pointing direction
GCTAPointing* pnt = dynamic_cast<GCTAPointing*>(obs.pointing());
if (pnt == NULL) {
std::string msg = "No CTA pointing found in observation.\n" +
obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
#endif
// Get reference to ROI centre
const GSkyDir& roi_centre = events->roi().centre().dir();
// Get ROI radius in radians
double roi_radius = events->roi().radius() * gammalib::deg2rad;
// Get distance from ROI centre in radians
#if defined(G_NPRED_AROUND_ROI)
double roi_distance = 0.0;
#else
double roi_distance = roi_centre.dist(pnt->dir());
#endif
// Initialise rotation matrix to transform from ROI system to
// celestial coordinate system
GMatrix ry;
GMatrix rz;
ry.eulery(roi_centre.dec_deg() - 90.0);
rz.eulerz(-roi_centre.ra_deg());
GMatrix rot = (ry * rz).transpose();
// Compute position angle of ROI centre with respect to model
// centre (radians)
#if defined(G_NPRED_AROUND_ROI)
double omega0 = 0.0;
#else
double omega0 = pnt->dir().posang(events->roi().centre().dir());
#endif
// Setup integration function
GCTAModelBackground::npred_roi_kern_theta integrand(spatial(),
obsEng,
obsTime,
rot,
roi_radius,
roi_distance,
omega0);
// Setup integrator
GIntegral integral(&integrand);
integral.eps(1e-3);
// Setup integration boundaries
#if defined(G_NPRED_AROUND_ROI)
double rmin = 0.0;
double rmax = roi_radius;
#else
double rmin = (roi_distance > roi_radius) ? roi_distance-roi_radius : 0.0;
double rmax = roi_radius + roi_distance;
#endif
// Spatially integrate radial component
npred = integral.romb(rmin, rmax);
// Store result in Npred cache
#if defined(G_USE_NPRED_CACHE)
m_npred_names.push_back(id);
m_npred_energies.push_back(obsEng);
m_npred_times.push_back(obsTime);
m_npred_values.push_back(npred);
#endif
// Debug: Check for NaN
#if defined(G_NAN_CHECK)
if (gammalib::is_notanumber(npred) || gammalib::is_infinite(npred)) {
std::cout << "*** ERROR: GCTAModelBackground::npred:";
std::cout << " NaN/Inf encountered";
std::cout << " (npred=" << npred;
std::cout << ", roi_radius=" << roi_radius;
std::cout << ")" << std::endl;
}
#endif
} // endif: model was valid
} // endif: Npred computation required
// Multiply in spectral and temporal components
npred *= spectral()->eval(obsEng, obsTime);
npred *= temporal()->eval(obsTime);
// Apply deadtime correction
npred *= obs.deadc(obsTime);
// Return Npred
return npred;
}
/***********************************************************************//**
* @brief Evaluate function and gradients
*
* @param[in] event Observed event.
* @param[in] obs Observation.
* @return Function value.
*
* @exception GException::invalid_argument
* No CTA instrument direction found in event.
*
* Evaluates tha CTA background model and parameter gradients. The CTA
* background model is a factorization of a spatial, spectral and
* temporal model component. This method also applies a deadtime correction
* factor, so that the normalization of the model is a real rate
* (counts/exposure time).
*
* @todo Add bookkeeping of last value and evaluate only if argument
* changed
***************************************************************************/
double GCTAModelBackground::eval_gradients(const GEvent& event,
const GObservation& obs) const
{
// Get pointer on CTA observation
const GCTAObservation* ctaobs = dynamic_cast<const GCTAObservation*>(&obs);
if (ctaobs == NULL) {
std::string msg = "Specified observation is not a CTA observation.\n" +
obs.print();
throw GException::invalid_argument(G_EVAL_GRADIENTS, msg);
}
// Extract CTA instrument direction
const GCTAInstDir* dir = dynamic_cast<const GCTAInstDir*>(&(event.dir()));
if (dir == NULL) {
std::string msg = "No CTA instrument direction found in event.";
throw GException::invalid_argument(G_EVAL_GRADIENTS, msg);
}
// Create a Photon from the event
// We need the photon to evaluate the spatial model
// For the background, GEvent and GPhoton are identical
// since the IRFs are not folded in
GPhoton photon = GPhoton(dir->dir(), event.energy(),event.time());
// Evaluate function and gradients
double spat = (spatial() != NULL)
? spatial()->eval_gradients(photon) : 1.0;
double spec = (spectral() != NULL)
? spectral()->eval_gradients(event.energy(), event.time()) : 1.0;
double temp = (temporal() != NULL)
? temporal()->eval_gradients(event.time()) : 1.0;
// Compute value
double value = spat * spec * temp;
// Apply deadtime correction
double deadc = obs.deadc(event.time());
value *= deadc;
// Multiply factors to spatial gradients
if (spatial() != NULL) {
double fact = spec * temp * deadc;
if (fact != 1.0) {
for (int i = 0; i < spatial()->size(); ++i)
(*spatial())[i].factor_gradient( (*spatial())[i].factor_gradient() * fact );
}
}
// Multiply factors to spectral gradients
if (spectral() != NULL) {
double fact = spat * temp * deadc;
if (fact != 1.0) {
for (int i = 0; i < spectral()->size(); ++i)
(*spectral())[i].factor_gradient( (*spectral())[i].factor_gradient() * fact );
}
}
// Multiply factors to temporal gradients
if (temporal() != NULL) {
double fact = spat * spec * deadc;
if (fact != 1.0) {
for (int i = 0; i < temporal()->size(); ++i)
(*temporal())[i].factor_gradient( (*temporal())[i].factor_gradient() * fact );
}
}
// Return value
return value;
}
/***********************************************************************//**
* @brief Return spatially integrated background model
*
* @param[in] obsEng Measured event energy.
* @param[in] obsTime Measured event time.
* @param[in] obs Observation.
* @return Spatially integrated model.
*
* @exception GException::invalid_argument
* The specified observation is not a CTA observation.
*
* Spatially integrates the effective area background model for a given
* measured event energy and event time. This method also applies a deadtime
* correction factor, so that the normalization of the model is a real rate
* (counts/MeV/s).
***************************************************************************/
double GCTAModelAeffBackground::npred(const GEnergy& obsEng,
const GTime& obsTime,
const GObservation& obs) const
{
// Set number of iterations for Romberg integration.
//static const int iter_theta = 6;
//static const int iter_phi = 6;
// Initialise result
double npred = 0.0;
bool has_npred = false;
// Build unique identifier
std::string id = obs.instrument() + "::" + obs.id();
// Check if Npred value is already in cache
#if defined(G_USE_NPRED_CACHE)
if (!m_npred_names.empty()) {
// Search for unique identifier, and if found, recover Npred value
// and break
for (int i = 0; i < m_npred_names.size(); ++i) {
if (m_npred_names[i] == id && m_npred_energies[i] == obsEng) {
npred = m_npred_values[i];
has_npred = true;
#if defined(G_DEBUG_NPRED)
std::cout << "GCTAModelAeffBackground::npred:";
std::cout << " cache=" << i;
std::cout << " npred=" << npred << std::endl;
#endif
break;
}
}
} // endif: there were values in the Npred cache
#endif
// Continue only if no Npred cache value has been found
if (!has_npred) {
// Evaluate only if model is valid
if (valid_model()) {
// Get log10 of energy in TeV
double logE = obsEng.log10TeV();
// Spatially integrate effective area component
npred = this->aeff_integral(obs, logE);
// Store result in Npred cache
#if defined(G_USE_NPRED_CACHE)
m_npred_names.push_back(id);
m_npred_energies.push_back(obsEng);
m_npred_times.push_back(obsTime);
m_npred_values.push_back(npred);
#endif
// Debug: Check for NaN
#if defined(G_NAN_CHECK)
if (gammalib::is_notanumber(npred) || gammalib::is_infinite(npred)) {
std::string origin = "GCTAModelAeffBackground::npred";
std::string message = " NaN/Inf encountered (npred=" +
gammalib::str(npred) + ")";
gammalib::warning(origin, message);
}
#endif
} // endif: model was valid
} // endif: Npred computation required
// Multiply in spectral and temporal components
npred *= spectral()->eval(obsEng, obsTime);
npred *= temporal()->eval(obsTime);
// Apply deadtime correction
npred *= obs.deadc(obsTime);
// Return Npred
return npred;
}
/***********************************************************************//**
* @brief Evaluate function
*
* @param[in] event Observed event.
* @param[in] obs Observation.
* @param[in] gradients Compute gradients?
* @return Function value.
*
* @exception GException::invalid_argument
* Specified observation is not of the expected type.
*
* If the @p gradients flag is true the method will also set the parameter
* gradients of the model parameters.
*
* @todo Make sure that DETX and DETY are always set in GCTAInstDir.
***************************************************************************/
double GCTAModelAeffBackground::eval(const GEvent& event,
const GObservation& obs,
const bool& gradients) const
{
// Get pointer on CTA observation
const GCTAObservation* cta = dynamic_cast<const GCTAObservation*>(&obs);
if (cta == NULL) {
std::string msg = "Specified observation is not a CTA observation.\n" +
obs.print();
throw GException::invalid_argument(G_EVAL, msg);
}
// Get pointer on CTA IRF response
const GCTAResponseIrf* rsp = dynamic_cast<const GCTAResponseIrf*>(cta->response());
if (rsp == NULL) {
std::string msg = "Specified observation does not contain an IRF response.\n" +
obs.print();
throw GException::invalid_argument(G_EVAL, msg);
}
// Retrieve pointer to CTA Effective Area
const GCTAAeff* aeff = rsp->aeff();
if (aeff == NULL) {
std::string msg = "Specified observation contains no effective area"
" information.\n" + obs.print();
throw GException::invalid_argument(G_EVAL, msg);
}
// Extract CTA instrument direction from event
const GCTAInstDir* dir = dynamic_cast<const GCTAInstDir*>(&(event.dir()));
if (dir == NULL) {
std::string msg = "No CTA instrument direction found in event.";
throw GException::invalid_argument(G_EVAL, msg);
}
// Set DETX and DETY in instrument direction
GCTAInstDir inst_dir = cta->pointing().instdir(dir->dir());
// Set theta and phi from instrument coordinates
double theta = std::sqrt(inst_dir.detx() * inst_dir.detx() +
inst_dir.dety() * inst_dir.dety());
double phi = gammalib::atan2d(inst_dir.dety(), inst_dir.detx()) *
gammalib::deg2rad;
// Evaluate function
double logE = event.energy().log10TeV();
double spat = (*aeff)(logE, theta, phi,
cta->pointing().zenith(),
cta->pointing().azimuth(), false);
double spec = (spectral() != NULL)
? spectral()->eval(event.energy(), event.time(), gradients)
: 1.0;
double temp = (temporal() != NULL)
? temporal()->eval(event.time(), gradients) : 1.0;
// Compute value
double value = spat * spec * temp;
// Apply deadtime correction
double deadc = obs.deadc(event.time());
value *= deadc;
// Optionally compute partial derivatives
if (gradients) {
// Multiply factors to spectral gradients
if (spectral() != NULL) {
double fact = spat * temp * deadc;
if (fact != 1.0) {
for (int i = 0; i < spectral()->size(); ++i)
(*spectral())[i].factor_gradient((*spectral())[i].factor_gradient() * fact );
}
}
// Multiply factors to temporal gradients
if (temporal() != NULL) {
double fact = spat * spec * deadc;
if (fact != 1.0) {
for (int i = 0; i < temporal()->size(); ++i)
(*temporal())[i].factor_gradient((*temporal())[i].factor_gradient() * fact );
}
}
} // endif: computed partial derivatives
// Return value
return value;
}
/***********************************************************************//**
* @brief Return spatially integrated background model
*
* @param[in] obsEng Measured event energy.
* @param[in] obsTime Measured event time.
* @param[in] obs Observation.
* @return Spatially integrated model.
*
* @exception GException::invalid_argument
* The specified observation is not a CTA observation.
*
* Spatially integrates the instrumental background model for a given
* measured event energy and event time. This method also applies a deadtime
* correction factor, so that the normalization of the model is a real rate
* (counts/MeV/s).
***************************************************************************/
double GCTAModelIrfBackground::npred(const GEnergy& obsEng,
const GTime& obsTime,
const GObservation& obs) const
{
// Initialise result
double npred = 0.0;
bool has_npred = false;
// Build unique identifier
std::string id = obs.instrument() + "::" + obs.id();
// Check if Npred value is already in cache
#if defined(G_USE_NPRED_CACHE)
if (!m_npred_names.empty()) {
// Search for unique identifier, and if found, recover Npred value
// and break
for (int i = 0; i < m_npred_names.size(); ++i) {
if (m_npred_names[i] == id && m_npred_energies[i] == obsEng) {
npred = m_npred_values[i];
has_npred = true;
#if defined(G_DEBUG_NPRED)
std::cout << "GCTAModelIrfBackground::npred:";
std::cout << " cache=" << i;
std::cout << " npred=" << npred << std::endl;
#endif
break;
}
}
} // endif: there were values in the Npred cache
#endif
// Continue only if no Npred cache value has been found
if (!has_npred) {
// Evaluate only if model is valid
if (valid_model()) {
// Get pointer on CTA observation
const GCTAObservation* cta = dynamic_cast<const GCTAObservation*>(&obs);
if (cta == NULL) {
std::string msg = "Specified observation is not a CTA"
" observation.\n" + obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
// Get pointer on CTA IRF response
const GCTAResponseIrf* rsp = dynamic_cast<const GCTAResponseIrf*>(cta->response());
if (rsp == NULL) {
std::string msg = "Specified observation does not contain"
" an IRF response.\n" + obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
// Retrieve pointer to CTA background
const GCTABackground* bgd = rsp->background();
if (bgd == NULL) {
std::string msg = "Specified observation contains no background"
" information.\n" + obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
// Get CTA event list
const GCTAEventList* events = dynamic_cast<const GCTAEventList*>(obs.events());
if (events == NULL) {
std::string msg = "No CTA event list found in observation.\n" +
obs.print();
throw GException::invalid_argument(G_NPRED, msg);
}
// Get reference to ROI centre
const GSkyDir& roi_centre = events->roi().centre().dir();
// Get ROI radius in radians
double roi_radius = events->roi().radius() * gammalib::deg2rad;
// Get log10 of energy in TeV
double logE = obsEng.log10TeV();
// Setup integration function
GCTAModelIrfBackground::npred_roi_kern_theta integrand(bgd, logE);
// Setup integrator
GIntegral integral(&integrand);
integral.eps(g_cta_inst_background_npred_theta_eps);
// Spatially integrate radial component
npred = integral.romberg(0.0, roi_radius);
// Store result in Npred cache
#if defined(G_USE_NPRED_CACHE)
m_npred_names.push_back(id);
m_npred_energies.push_back(obsEng);
m_npred_times.push_back(obsTime);
m_npred_values.push_back(npred);
#endif
// Debug: Check for NaN
#if defined(G_NAN_CHECK)
if (gammalib::is_notanumber(npred) || gammalib::is_infinite(npred)) {
std::string origin = "GCTAModelIrfBackground::npred";
std::string message = " NaN/Inf encountered (npred=" +
gammalib::str(npred) + ", roi_radius=" +
gammalib::str(roi_radius) + ")";
gammalib::warning(origin, message);
}
#endif
} // endif: model was valid
} // endif: Npred computation required
// Multiply in spectral and temporal components
npred *= spectral()->eval(obsEng, obsTime);
npred *= temporal()->eval(obsTime);
// Apply deadtime correction
npred *= obs.deadc(obsTime);
// Return Npred
return npred;
}
/***********************************************************************//**
* @brief Return value of instrument response function
*
* @param[in] event Observed event.
* @param[in] photon Incident photon.
* @param[in] obs Observation.
* @return Instrument response function (cm2 sr-1)
*
* @exception GException::invalid_argument
* Observation is not a COMPTEL observation.
* Event is not a COMPTEL event bin.
*
* Returns the instrument response function for a given observed photon
* direction as function of the assumed true photon direction. The result
* is given by
* \f[IRF = \frac{IAQ \times DRG \times DRX}{ontime \times ewidth}\f]
* where
* \f$IRF\f$ is the instrument response function,
* \f$IAQ\f$ is the COMPTEL response matrix (sr-1),
* \f$DRG\f$ is the geometry factor (cm2),
* \f$DRX\f$ is the exposure (s),
* \f$ontime\f$ is the ontime (s), and
* \f$ewidth\f$ is the energy width (MeV).
*
* The observed photon direction is spanned by the 3 values (Chi,Psi,Phibar).
* (Chi,Psi) is the scatter direction of the event, given in sky coordinates.
* Phibar is the Compton scatter angle, computed from the energy deposits.
***************************************************************************/
double GCOMResponse::irf(const GEvent& event,
const GPhoton& photon,
const GObservation& obs) const
{
// Extract COMPTEL observation
const GCOMObservation* observation = dynamic_cast<const GCOMObservation*>(&obs);
if (observation == NULL) {
std::string cls = std::string(typeid(&obs).name());
std::string msg = "Observation of type \""+cls+"\" is not a COMPTEL "
"observations. Please specify a COMPTEL observation "
"as argument.";
throw GException::invalid_argument(G_IRF, msg);
}
// Extract COMPTEL event bin
const GCOMEventBin* bin = dynamic_cast<const GCOMEventBin*>(&event);
if (bin == NULL) {
std::string cls = std::string(typeid(&event).name());
std::string msg = "Event of type \""+cls+"\" is not a COMPTEL event. "
"Please specify a COMPTEL event as argument.";
throw GException::invalid_argument(G_IRF, msg);
}
// Extract event parameters
const GCOMInstDir& obsDir = bin->dir();
// Extract photon parameters
const GSkyDir& srcDir = photon.dir();
const GTime& srcTime = photon.time();
// Compute angle between true photon arrival direction and scatter
// direction (Chi,Psi)
double phigeo = srcDir.dist_deg(obsDir.dir());
// Compute scatter angle index
int iphibar = int(obsDir.phibar() / m_phibar_bin_size);
// Extract IAQ value by linear inter/extrapolation in Phigeo
double iaq = 0.0;
if (iphibar < m_phibar_bins) {
double phirat = phigeo / m_phigeo_bin_size; // 0.5 at bin centre
int iphigeo = int(phirat); // index into which Phigeo falls
double eps = phirat - iphigeo - 0.5; // 0.0 at bin centre
if (iphigeo < m_phigeo_bins) {
int i = iphibar * m_phigeo_bins + iphigeo;
if (eps < 0.0) { // interpolate towards left
if (iphigeo > 0) {
iaq = (1.0 + eps) * m_iaq[i] - eps * m_iaq[i-1];
}
else {
iaq = (1.0 - eps) * m_iaq[i] + eps * m_iaq[i+1];
}
}
else { // interpolate towards right
if (iphigeo < m_phigeo_bins-1) {
iaq = (1.0 - eps) * m_iaq[i] + eps * m_iaq[i+1];
}
else {
iaq = (1.0 + eps) * m_iaq[i] - eps * m_iaq[i-1];
}
}
}
}
// Get DRG value (units: cm2)
double drg = observation->drg()(obsDir.dir(), iphibar);
// Get DRX value (units: sec)
double drx = observation->drx()(srcDir);
// Get ontime
double ontime = observation->ontime(); // sec
// Compute IRF value
double irf = iaq * drg * drx / ontime;
// Apply deadtime correction
irf *= obs.deadc(srcTime);
// Compile option: Check for NaN/Inf
#if defined(G_NAN_CHECK)
if (gammalib::is_notanumber(irf) || gammalib::is_infinite(irf)) {
std::cout << "*** ERROR: GCOMResponse::irf:";
std::cout << " NaN/Inf encountered";
std::cout << " (irf=" << irf;
std::cout << ", iaq=" << iaq;
std::cout << ", drg=" << drg;
std::cout << ", drx=" << drx;
std::cout << ")";
std::cout << std::endl;
}
#endif
// Return IRF value
return irf;
}