Veronika Vodeb / ctools

/***************************************************************************
 *                       ctskymap - Sky mapping tool                       *
 * ----------------------------------------------------------------------- *
 *  copyright (C) 2011-2017 by Juergen Knoedlseder                         *
 * ----------------------------------------------------------------------- *
 *                                                                         *
 *  This program is free software: you can redistribute it and/or modify   *
 *  it under the terms of the GNU General Public License as published by   *
 *  the Free Software Foundation, either version 3 of the License, or      *
 *  (at your option) any later version.                                    *
 *                                                                         *
 *  This program is distributed in the hope that it will be useful,        *
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of         *
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          *
 *  GNU General Public License for more details.                           *
 *                                                                         *
 *  You should have received a copy of the GNU General Public License      *
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.  *
 *                                                                         *
 ***************************************************************************/
/**
 * @file ctskymap.cpp
 * @brief Sky mapping tool implementation
 * @author Juergen Knoedlseder
 */

/* __ Includes ___________________________________________________________ */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <cstdio>
#include "ctskymap.hpp"
#include "GSkyRegions.hpp"

/* __ Method name definitions ____________________________________________ */
#define G_INIT_MAP                  "ctskymap::init_map(GCTAObservation* obs)"
#define G_BIN_EVENTS                  "ctskymap::map_events(GCTAObservation*)"
#define G_BKG_SUBTRACT_IRF    "ctskymap::map_background_irf(GCTAObservation*)"
#define G_BKG_SUBTRACT_RING  "ctskymap::map_background_ring(GCTAObservation*)"

/* __ Debug definitions __________________________________________________ */

/* __ Coding definitions _________________________________________________ */


/*==========================================================================
 =                                                                         =
 =                        Constructors/destructors                         =
 =                                                                         =
 ==========================================================================*/

/***********************************************************************//**
 * @brief Void constructor
 *
 * Constructs an empty sky mapping tool.
 ***************************************************************************/
ctskymap::ctskymap(void) : ctobservation(CTSKYMAP_NAME, VERSION)
{
    // Initialise members
    init_members();

    // Return
    return;
}


/***********************************************************************//**
 * @brief Observations constructor
 *
 * param[in] obs Observation container.
 *
 * Constructs sky mapping tool from an observation container.
 ***************************************************************************/
ctskymap::ctskymap(const GObservations& obs) :
          ctobservation(CTSKYMAP_NAME, VERSION, obs)
{
    // Initialise members
    init_members();

    // Return
    return;
}



/***********************************************************************//**
 * @brief Command line constructor
 *
 * @param[in] argc Number of arguments in command line.
 * @param[in] argv Array of command line arguments.
 *
 * Constructs sky mapping tool using command line arguments for user
 * parameter setting.
 ***************************************************************************/
ctskymap::ctskymap(int argc, char *argv[]) : 
          ctobservation(CTSKYMAP_NAME, VERSION, argc, argv)
{
    // Initialise members
    init_members();

    // Return
    return;
}


/***********************************************************************//**
 * @brief Copy constructor
 *
 * @param[in] app Sky mapping tool.
 ***************************************************************************/
ctskymap::ctskymap(const ctskymap& app) : ctobservation(app)
{
    // Initialise members
    init_members();

    // Copy members
    copy_members(app);

    // Return
    return;
}


/***********************************************************************//**
 * @brief Destructor
 ***************************************************************************/
ctskymap::~ctskymap(void)
{
    // Free members
    free_members();

    // Return
    return;
}


/*==========================================================================
 =                                                                         =
 =                               Operators                                 =
 =                                                                         =
 ==========================================================================*/

/***********************************************************************//**
 * @brief Assignment operator
 *
 * @param[in] app Sky mapping tool.
 * @return Sky mapping tool.
 ***************************************************************************/
ctskymap& ctskymap::operator=(const ctskymap& app)
{
    // Execute only if object is not identical
    if (this != &app) {

        // Copy base class members
        this->ctobservation::operator=(app);

        // Free members
        free_members();

        // Initialise members
        init_members();

        // Copy members
        copy_members(app);

    } // endif: object was not identical

    // Return this object
    return *this;
}


/*==========================================================================
 =                                                                         =
 =                            Public methods                               =
 =                                                                         =
 ==========================================================================*/

/***********************************************************************//**
 * @brief Clear sky mapping tool
 *
 * Clears sky mapping tool.
 ***************************************************************************/
void ctskymap::clear(void)
{
    // Free members
    free_members();
    this->ctool::free_members();
    this->ctobservation::free_members();

    // Clear base class (needed to conserve tool name and version)
    this->GApplication::clear();

    // Initialise members
    this->ctool::init_members();
    this->ctobservation::init_members();
    init_members();

    // Write header into logger
    log_header();

    // Return
    return;
}


/***********************************************************************//**
 * @brief Run the sky mapping tool
 *
 * Generates a sky map from event list by looping over all unbinned CTA
 * observation in the observation container and filling all events into
 * a sky map.
 ***************************************************************************/
void ctskymap::run(void)
{
    // Switch screen logging on in debug mode
    if (logDebug()) {
        log.cout(true);
    }

    // Get parameters
    get_parameters();

    // Write input observation container into logger
    log_observations(NORMAL, m_obs, "Input observation");

    // Write header into logger
    log_header1(TERSE, gammalib::number("Map observation", m_obs.size()));

    // Loop over all unbinned CTA observations in the container
    for (GCTAObservation* obs = first_unbinned_observation(); obs != NULL;
         obs = next_unbinned_observation()) {

        // Map events into sky map
        map_events(obs);

        // Compute background sky map
        map_background(obs);

        // Dispose events to free memory
        obs->dispose_events();

    } // endfor: looped over observations

    // Compute the significance map
    map_significance();
    
    // Optionally publish sky map
    if (m_publish) {
        publish();
    }

    // Return
    return;
}


/***********************************************************************//**
 * @brief Save sky map
 *
 * Saves the sky map into a FITS file. The FITS file name is specified by the
 * @p outname parameter.
 ***************************************************************************/
void ctskymap::save(void)
{
    // Write header
    log_header1(TERSE, "Save sky map");

    // Get sky map filename
    m_outmap  = (*this)["outmap"].filename();

    // Save sky map if filename and the map are not empty
    if (!m_outmap.is_empty() && !m_skymap.is_empty()) {

        // Create empty FITS file
        GFits fits;

        // Write sky map into FITS file
        m_skymap.write(fits);

        // If background subtraction is requested then write background map
        // and significance map to FITS file
        if (m_bkgsubtract != "NONE") {
        
            // Write background map into FITS file
            m_bkgmap.write(fits);

            // Set background map extension name
            fits[fits.size()-1]->extname("BACKGROUND");

            // Write significance map into FITS file
            m_sigmap.write(fits);

            // Set significance map extension name
            fits[fits.size()-1]->extname("SIGNIFICANCE");

        } // endif: background subtraction was requested

        // Save FITS file to disk
        fits.saveto(m_outmap, clobber());

    }

    // Write into logger what has been done
    std::string fname = (m_outmap.is_empty()) ? "NONE" : m_outmap.url();
    if (m_skymap.is_empty()) {
        fname.append(" (map is empty, no file created)");
    }
    log_value(NORMAL, "Sky map file", fname);

    // Return
    return;
}


/***********************************************************************//**
 * @brief Publish sky map
 *
 * @param[in] name Sky map name.
 ***************************************************************************/
void ctskymap::publish(const std::string& name)
{
    // Write header into logger
    log_header1(TERSE, "Publish sky map");

    // Set default name if user name is empty
    std::string user_name(name);
    if (user_name.empty()) {
        user_name = CTSKYMAP_NAME;
    }

    // Write sky map name into logger
    log_value(NORMAL, "Sky map name", user_name);

    // Publish sky map
    m_skymap.publish(user_name);

    // Return
    return;
}


/*==========================================================================
 =                                                                         =
 =                             Private methods                             =
 =                                                                         =
 ==========================================================================*/

/***********************************************************************//**
 * @brief Initialise class members
 ***************************************************************************/
void ctskymap::init_members(void)
{
    // Initialise members
    m_skymap.clear();
    m_bkgmap.clear();
    m_sigmap.clear();
    m_emin        = 0.0;
    m_emax        = 0.0;
    m_bkgsubtract = "NONE";
    m_publish     = false;
    m_chatter     = static_cast<GChatter>(2);
    m_solidangle  = std::vector<double>(0);

    // Variables for RING bkgd subtraction
    m_exclmap.clear();
    m_roiradius = 0.0;
    m_inradius  = 0.0;
    m_outradius = 0.0;
    m_cnts = std::vector<int>(0);

    // Return
    return;
}


/***********************************************************************//**
 * @brief Copy class members
 *
 * @param[in] app Application.
 ***************************************************************************/
void ctskymap::copy_members(const ctskymap& app)
{
    // Copy attributes
    m_skymap      = app.m_skymap;
    m_bkgmap      = app.m_bkgmap;
    m_sigmap      = app.m_sigmap;
    m_emin        = app.m_emin;
    m_emax        = app.m_emax;
    m_bkgsubtract = app.m_bkgsubtract;
    m_publish     = app.m_publish;
    m_chatter     = app.m_chatter;
    m_solidangle = app.m_solidangle;

    // Variables for RING bkgd subtraction
    m_exclmap = app.m_exclmap;
    m_roiradius = app.m_roiradius;
    m_inradius  = app.m_inradius;
    m_outradius = app.m_outradius;
    m_cnts = app.m_cnts;

    // Return
    return;
}


/***********************************************************************//**
 * @brief Delete class members
 ***************************************************************************/
void ctskymap::free_members(void)
{
    // Return
    return;
}


/***********************************************************************//**
 * @brief Get application parameters
 *
 * Get all task parameters from parameter file or (if required) by querying
 * the user. Most parameters are only required if no observation exists so
 * far in the observation container. In this case, a single CTA observation
 * will be added to the container, using the definition provided in the
 * parameter file.
 ***************************************************************************/
void ctskymap::get_parameters(void)
{
    // Setup observations from "inobs" parameter. Do not request response
    // information and do not accept counts cubes.
    setup_observations(m_obs, false, true, false);

    // Create sky map based on task parameters
    m_skymap = create_map(m_obs);

    // Get further parameters
    m_emin        = (*this)["emin"].real();
    m_emax        = (*this)["emax"].real();
    m_bkgsubtract = (*this)["bkgsubtract"].string();

    // If IRF background subtraction is requested then make sure that the
    // CTA observations in the observation container have response information
    if (m_bkgsubtract == "IRF") {
        set_response(m_obs);
    }

    // Get remaining parameters
    m_publish     = (*this)["publish"].boolean();
    m_chatter     = static_cast<GChatter>((*this)["chatter"].integer());

    // Read ahead parameters
    if (read_ahead()) {
        m_outmap    = (*this)["outmap"].filename();

        if (m_bkgsubtract == "RING") {
            // Get the integration region radii
            m_roiradius = (*this)["roiradius"].real();
            m_inradius  = (*this)["inradius"].real();
            m_outradius = (*this)["outradius"].real();

            // Make sure the values are reasonable
            if (m_roiradius > m_inradius) {
                std::string err("'roiradius' must be smaller than inner ring radius");
                throw GException::invalid_value(err);
            } else if (m_inradius > m_outradius) {
                std::string err("Inner ring radius must be smaller than outer ring radius");
                throw GException::invalid_value(err);
            } // endif: Ring radius checks
        }
    }

    // Create background map and significance map if background subtraction
    // is requested
    if (m_bkgsubtract != "NONE") {
        m_bkgmap = create_map(m_obs);
        m_sigmap = create_map(m_obs);
        
        // Setup the exclusions map
        map_exclusions((*this)["regfile"].filename());

        // If doing a ring background subtraction, generate an alpha map
        if (m_bkgsubtract == "RING") {
            m_cnts = std::vector<int>(m_bkgmap.npix(), 0);
        }

        // Cache the pixel solid angles
        m_solidangle = std::vector<double>(m_bkgmap.npix(), 0.0);
        for (int i=0; i<m_bkgmap.npix(); i++) {
            m_solidangle[i] = m_bkgmap.solidangle(i);
        }
    }

    // Write parameters into logger
    log_parameters(TERSE);

    // Return
    return;
}


/***********************************************************************//**
 * @brief Map events into a sky map
 *
 * @param[in] obs CTA observation.
 *
 * @exception GException::no_list
 *            No event list found in observation.
 *
 * This method maps the events found in a CTA events list into a sky map.
 ***************************************************************************/
void ctskymap::map_events(GCTAObservation* obs)
{
    // Get non-const pointer on a CTA event list
    GCTAEventList* events = dynamic_cast<GCTAEventList*>
                            (const_cast<GEvents*>(obs->events()));

    // Make sure that the observation holds a CTA event list. If this
    // is not the case then throw an exception.
    if (events == NULL) {
        throw GException::no_list(G_BIN_EVENTS);
    }

    // Setup energy range covered by data
    GEnergy  emin;
    GEnergy  emax;
    GEbounds ebds;
    emin.TeV(m_emin);
    emax.TeV(m_emax);

    // Initialise binning statistics
    int num_outside_roi    = 0;
    int num_outside_map    = 0;
    int num_outside_erange = 0;
    int num_in_map         = 0;

    // Extract region of interest from observation
    GCTARoi roi = obs->roi();

    // Fill sky map
    for (int i = 0; i < events->size(); ++i) {

        // Get event
        GCTAEventAtom* event = (*events)[i];

        // Skip if energy is out of range
        if (event->energy() < emin || event->energy() > emax) {
            num_outside_erange++;
            continue;
        }

        // Determine sky pixel
        GCTAInstDir* inst  = (GCTAInstDir*)&(event->dir());
        GSkyDir      dir   = inst->dir();
        GSkyPixel    pixel = m_skymap.dir2pix(dir);

        // Skip if pixel is out of range
        if (pixel.x() < -0.5 || pixel.x() > (m_skymap.nx() - 0.5) ||
            pixel.y() < -0.5 || pixel.y() > (m_skymap.ny() - 0.5)) {
            num_outside_map++;
            continue;
        }

        // If RoI is valid then skip if  instrument direction is not within RoI
        if (roi.is_valid() && !roi.contains(*inst)) {
            continue;
            num_outside_roi++;
        }

        // Fill event in skymap
        m_skymap(pixel, 0) += 1.0;
        num_in_map++;

        // If doing the RING subtraction, keep tabs on counts from this obs
        if (m_bkgsubtract == "RING") {
            m_cnts[m_skymap.pix2inx(pixel)] += 1.0;
        }
        
    } // endfor: looped over all events

    // Log binning results
    log_value(NORMAL, "Events in list", obs->events()->size());
    log_value(NORMAL, "Events in map", num_in_map);
    log_value(NORMAL, "Events outside RoI", num_outside_roi);
    log_value(NORMAL, "Events outside map area", num_outside_map);
    log_value(NORMAL, "Events outside energies", num_outside_erange);

    // Write sky map into header
    log_header2(EXPLICIT, "Sky map");
    log_string(EXPLICIT, m_skymap.print(m_chatter));

    // Return
    return;
}


/***********************************************************************//**
 * @brief Estimates the background in sky map for observation
 *
 * @param[in] obs CTA observation.
 *
 * Estimates the background in the sky map for a given observation and adds
 * this estimate to the background sky map. The background estimation method
 * is specified by the "bkgsubtract" parameter which can take the following
 * values:
 *
 *     NONE - No background estimation
 *     IRF  - Background estimation based on IRF template
 ***************************************************************************/
void ctskymap::map_background(GCTAObservation* obs)
{
    // Dispatch to appropriate background estimation method
    if (m_bkgsubtract == "IRF") {
        map_background_irf(obs);
    } else if (m_bkgsubtract == "RING") {
        map_background_ring(obs);
    }

    // Return
    return;
}


/***********************************************************************//**
 * @brief Estimates the background in sky map based on IRF template
 *
 * @param[in] obs CTA observation.
 *
 * @exception GException::invalid_value
 *            No response information available for observation.
 *            No background template available in instrument response function.
 *
 * Estimates the background in the sky map using the IRF template for a given
 * observation and adds this estimate to the background sky map. The IRF
 * template is integrated numerically in energy.
 ***************************************************************************/
void ctskymap::map_background_irf(GCTAObservation* obs)
{
    // Get IRF response
    const GCTAResponseIrf* rsp = dynamic_cast<const GCTAResponseIrf*>(obs->response());

    // Throw an exception if observation has no instrument response function
    if (rsp == NULL) {
        std::string msg = "No response information available for "+
                          get_obs_header(obs)+" to compute IRF background. "
                          "Please specify response information or use "
                          "another background subtraction method.";
        throw GException::invalid_value(G_BKG_SUBTRACT_IRF, msg);
    }

    // Get IRF background template
    const GCTABackground* bkg = rsp->background();

    // Throw an exception if observation has no IRF background template
    if (bkg == NULL) {
        std::string msg = "No IRF background template found in instrument "
                          "response function for "+
                          get_obs_header(obs)+". Please specify an instrument "
                          "response function containing a background template.";
        throw GException::invalid_value(G_BKG_SUBTRACT_IRF, msg);
    }

    // Compute natural logarithm of energy range in MeV
    double lnEmin = std::log(m_emin * 1.0e6);
    double lnEmax = std::log(m_emax * 1.0e6);

    // Extract region of interest from observation
    GCTARoi roi = obs->roi();

    // Initialise statistics
    int    calls = 0;
    double total = 0.0;

    // Loop over all background map pixels
    for (int i = 0; i < m_bkgmap.npix(); ++i) {

        // Get sky direction of pixel
        GSkyDir skydir = m_bkgmap.inx2dir(i);

        // Convert sky direction in instrument direction
        GCTAInstDir instdir = obs->pointing().instdir(skydir);

        // If RoI is valid and instrument direction is not within RoI then
        // skip pixel
        if (roi.is_valid() && !roi.contains(instdir)) {
            continue;
        }

        // Setup integration function
        ctskymap::irf_kern integrand(bkg, &instdir);
        GIntegral          integral(&integrand);

        // Set precision (has been carefully adjusted using a test simulation
        // over the energy range 20 GeV - 120 TeV)
        integral.eps(1.0e-6);

        // Do Romberg integration
        double value = integral.romberg(lnEmin, lnEmax);

        // Update number of background function calls
        calls += integral.calls();
        
        // Multiply background rate with livetime and solid angle
        value *= obs->livetime() * m_bkgmap.solidangle(i);

        // Add number of background events to background map
        m_bkgmap(i,0) += value;

        // Update total number of background events
        total += value;

    } // endfor: looped over background map pixels

    // Log background subtraction results
    log_value(NORMAL, "Events in background", int(total+0.5));
    log_value(NORMAL, "Background evaluations", calls);

    // Return
    return;
}


/***********************************************************************//**
 * @brief Estimates the background in sky map based on the ring background method
 *
 * @param[in] obs CTA observation.
 *
 * @exception GException::invalid_value
 *            No response information available for observation.
 *            No background template available in instrument response function.
 *
 * Estimates the background in the sky map by summing the events within a ring
 * centered at a given pixel's position. The pixels in the ring are weighted
 * also by the background IRF value
 ***************************************************************************/
void ctskymap::map_background_ring(GCTAObservation* obs)
{
    // Get IRF response (to scale background counts)
    const GCTAResponseIrf* rsp = dynamic_cast<const GCTAResponseIrf*>(obs->response());

        // Throw an exception if observation has no instrument response function
    if (rsp == NULL) {
        std::string msg = "No response information available for "+
                          get_obs_header(obs)+" to compute IRF background. "
                          "Please specify response information or use "
                          "another background subtraction method.";
        throw GException::invalid_value(G_BKG_SUBTRACT_IRF, msg);
    }

    // Get IRF background template
    const GCTABackground* bkg = rsp->background();

    // Throw an exception if observation has no IRF background template
    if (bkg == NULL) {
        std::string msg = "No IRF background template found in instrument "
                          "response function for "+
                          get_obs_header(obs)+". Please specify an instrument "
                          "response function containing a background template.";
        throw GException::invalid_value(G_BKG_SUBTRACT_IRF, msg);
    }

    // Compute natural logarithm of energy range in MeV
    double lnEmin = std::log(m_emin * 1.0e6);
    double lnEmax = std::log(m_emax * 1.0e6);

    // Extract region of interest from observation
    GCTARoi roi = obs->roi();

    // Initialise statistics
    int    calls = 0;
    double total = 0.0;
    double exposure = obs->livetime() ;

    // Cached background IRF sensitivities
    std::vector<double> sens(m_cnts.size(), 0.0);  
    std::vector<bool>   obsoverlap(m_cnts.size(), false);

    // Cache the IRF sensitivities
    // Loop over all map pixels
    for (int i = 0; i < m_bkgmap.npix(); ++i) {

        // Get sky direction of pixel
        GSkyDir skydir = m_bkgmap.inx2dir(i);

        // Convert sky direction in instrument direction
        GCTAInstDir instdir = obs->pointing().instdir(skydir);
    
        // If RoI is valid and instrument direction is not within RoI then
        // skip pixel
        if (roi.is_valid() && !roi.contains(instdir)) {
            continue;
        }

        // Notify that this bin overlaps the observation
        obsoverlap[i] = true;

        // If bin is excluded in the exclusion, skip it
        if (m_exclmap(i) == 0.0) {
            continue;
        }

        // Setup integration function
        ctskymap::irf_kern integrand(bkg, &instdir);
        GIntegral          integral(&integrand);

        // Set precision (has been carefully adjusted using a test simulation
        // over the energy range 20 GeV - 120 TeV)
        integral.eps(1.0e-6);

        // Do Romberg integration to get the sensitivity (note: this assumes the
        // background IRF is a good approximation for the radial sensitivity)
        sens[i] = integral.romberg(lnEmin, lnEmax);

        // Update number of background function calls
        calls += integral.calls();

    } // endfor: Loop for caching bkg IRF sensitivity

    // Define the regions necessary to do the pixel checks
    GSkyRegionCircle roi_reg(0.0, 0.0, m_roiradius);
    GSkyRegionCircle inner_reg(0.0, 0.0, m_inradius);
    GSkyRegionCircle outer_reg(0.0, 0.0, m_outradius);

log_string(NORMAL, "LOOPING ON BKG IRF DONE");
log_string(NORMAL, "LOOPING ON EVENTS!");
    // Loop over all map pixels
    for (int i = 0; i < m_bkgmap.npix(); ++i) {

        log_value(NORMAL, "PIXEL #", i);

        if (!obsoverlap[i]) {
            continue;
        }

        // Update the region positions
        roi_reg.centre(skydir);
        inner_reg.centre(skydir);
        outer_reg.centre(skydir);

        // Loop again over every pixel in the observation to compute Non/Noff
        int n_on(0), n_off(0);
        double alpha_on(0.0), alpha_off(0.0);
        for (int j = 0; j < m_bkgmap.npix(); ++j) {

            // Check if the observation overlaps this pixel
            if (!obsoverlap[j]) {
                continue;
            }

            // Get sky direction of pixel
            skydir = m_bkgmap.inx2dir(i);

            // Check if pixel is inside source region
            if (roi_reg.contains(skydir)) {
                // Update n_on
                n_on += m_cnts[j];

                // Update alpha_on
                alpha_on += m_solidangle[j] * sens[j];
            }

            // Otherwise check if it is in the background region
            else if ((m_exclmap(j) == 1.0) &&
                     !inner_reg.contains(skydir) &&
                     outer_reg.contains(skydir)) {
                // Update n_off
                n_off += m_cnts[j];

                // Update alpha_off
                alpha_off += m_solidangle[j] * sens[j];
            }
            
        } // endfor: sub-loop over pixels

        // Compute the likelihood for this bin
        double alpha = alpha_on / alpha_off;
        m_sigmap(i,0) += std::log(1);

        // Update the predicted background counts
        m_bkgmap(i,0) = n_on - (alpha * n_off);

    } // endfor: looped over background map pixels

    // Zero out the alpha map to prepare it for the next observation
    std::vector<int>::iterator iter;
    for (iter=m_cnts.begin(); iter!=m_cnts.end(); ++iter) {
        (*iter) = 0;
    }

    // Return
    return;
}


/***********************************************************************//**
 * @brief Computes the bin-by-bin significance if background subtraction requested
 *
 * Method computes the bin-by bin significance if a background subtraction 
 * method is specified. If method is "IRF", Poisson statistics (in the Gaussian
 * limit) are assumed. If method is "RING" a Li & Ma significance is computed
 * for each bin (as well as a map of the computed alpha values). 
 ***************************************************************************/
void ctskymap::map_significance(void)
{
    // Check if no background subtraction is requested
    if (m_bkgsubtract == "NONE") {
        return;
    }

    // If background subtract was required then compute significance map..

    // ... from "RING" method (Li & Ma eq. 17)
    else if (m_bkgsubtract == "RING") {
        // Multiply the significance map by '-2'
        m_sigmap *= -2.0;

        // Now the square root
        m_sigmap = sqrt(m_sigmap);
    } 

    // ... using Poisson statistics in the Gaussian limit
    else {
        // Compute significance map
        m_sigmap = (m_skymap - m_bkgmap) / sqrt(m_skymap);
    } // endif: background subtraction was requested
    
    // Subtract background map from counts map
    m_skymap -= m_bkgmap;
}


/***********************************************************************//**
 * @brief Generates a map of pixels to be excluded from background estimation
 *
 * @param[in] filename Filename from which to take the exclusions from
 ***************************************************************************/
void ctskymap::map_exclusions(const GFilename& filename)
{
    // Otherwise, create the map and set all pixels to 1
    m_exclmap = create_map(m_obs);
    m_exclmap = 1.0;

    // Make sure the exclusions filename is valid
    if (!is_valid_filename(filename)) {
        return;
    }

    // Fill the exclusions based on the regions supplied
    if (filename.is_fits()) {
        map_exclusions_fits(filename);
    } else {
        map_exclusions_reg(filename);
    } // endif: generate exclusion map from filename

    return;
}


/***********************************************************************//**
 * @brief Fills exclusions map if file is a FITS image
 *
 * @param[in] filename Filename from which to take the exclusions from
 ***************************************************************************/
void ctskymap::map_exclusions_fits(const GFilename& filename)
{
    // Load the fits image
    GSkyMap inmap(filename);

    // Loop through the individual pixels in the exclusion map
    GSkyDir dir;
    for (int i=0; i<m_exclmap.npix(); i++) {
        // Get the pixel direction
        dir = m_exclmap.pix2dir(i);

        // Check this sky position in the fits map
        if (inmap.contains(dir) && (inmap(inmap.dir2inx(dir)) == 0.0)) {
            // Set the pixel to 0
            m_exclmap(i) = 0.0;

        } // endif: pixel,region overlap check
    } // endfor: Loop over exclusion map pixels
}


/***********************************************************************//**
 * @brief Fills exclusions map if file is a DS9 region file
 *
 * @param[in] filename Filename from which to take the exclusions from
 ***************************************************************************/
void ctskymap::map_exclusions_reg(const GFilename& filename)
{
    // Load the exclusion regions
    GSkyRegions regions(filename);

    // Loop through the individual pixels in the exclusion map
    GSkyDir dir;
    for (int i=0; i<m_exclmap.npix(); i++) {
        // Get the pixel position
        dir = m_exclmap.pix2dir(i);

        // Check if GSkyDir overlaps with the regions
        if (regions.contains(dir)) {
            // Set the pixel to 0
            m_exclmap(i) = 0.0;

        } // endif: pixel,region overlap check
    } // endfor: loop over exclusion map pixels
}


/***********************************************************************//**
 * @brief Estimates the background in sky map based on IRF template
 *
 * @param[in] lnE Natural logarithm of energy in MeV.
 ***************************************************************************/
double ctskymap::irf_kern::eval(const double& lnE)
{
    // Get log10 of energy in TeV
    double logE = lnE * gammalib::inv_ln10 - 6;

    // Get function value
    double value = (*m_bgd)(logE, m_dir->detx(), m_dir->dety());

    // Correct for variable substitution
    value *= std::exp(lnE);

    // Return value
    return value;
}