ctools

I ran ctbin on a 3.7 GB events.fits input file generated with ctobssim. It prompts for the filename

Input event list or observation definition file [mucho_events.fits] 

and when I hit enter it reads the 3.7 GB from disk (and makes me wait for a long time) before prompting for the next parameter:

Start value for first energy bin in TeV [0.1]

and all the other parameters.

I think all tools (I didn’t check the others) should first read all parameters, then process the data while I go for a coffee.
Would there be a problem changing ctbin to work that way?

The “problem” is that ctbin::get_parameters calls obs.load_unbinned(m_evfile); before getting the remaining parameters:

void ctbin::get_parameters(void)
{
    // If there are no observations in container then add a single CTA
    // observation using the parameters from the parameter file
    if (m_obs.size() == 0) {

        // Get name of CTA events file
        m_evfile = (*this)["evfile"].filename();

        // Allocate CTA observation
        GCTAObservation obs;

        // Try first to open as FITS file
        try {

            // Load event list in CTA observation
            obs.load_unbinned(m_evfile);

            // Append CTA observation to container
            m_obs.append(obs);

            // Signal that no XML file should be used for storage
            m_use_xml = false;

        }

        // ... otherwise try to open as XML file
        catch (GException::fits_open_error &e) {

            // Load observations from XML file
            m_obs.load(m_evfile);

            // Signal that XML file should be used for storage
            m_use_xml = true;

        }

        // Use the xref and yref parameters for binning (otherwise the
        // pointing direction(s) is/are used)
        //m_xref = (*this)["xref"].real();
        //m_yref = (*this)["yref"].real();

    } // endif: there was no observation in the container

    // Get remaining parameters
    m_emin     = (*this)["emin"].real();
    m_emax     = (*this)["emax"].real();
    m_enumbins = (*this)["enumbins"].integer();
    m_proj     = (*this)["proj"].string();
    m_coordsys = (*this)["coordsys"].string();
    m_xref     = (*this)["xref"].real();
    m_yref     = (*this)["yref"].real();
    m_binsz    = (*this)["binsz"].real();
    m_nxpix    = (*this)["nxpix"].integer();
    m_nypix    = (*this)["nypix"].integer();

    // Optionally read ahead parameters so that they get correctly
    // dumped into the log file
    if (m_read_ahead) {
        m_outfile = (*this)["outfile"].filename();
        m_prefix  = (*this)["prefix"].string();
    }

    // Return
    return;
}