Subject: Common structure / function for event access


  Dear all,

  during our meeting at DSRI, Niels Jørgen, Stefan and I had
some discussion about shared functions. One of the agreed
propositions was that while DAL3JEMX prefers to give you
access column by column to event data - which saves memory 
and some read overhead - we usually need to have (almost)
all this information anyhow. Instead of having N loosely
related arrays, software would be more reader friendly
and function interfaces could be simplified in the future 
if we had a C struct for events and a single function to 
read all event information of a ScW matching some selection.

  My action was to propose the interface for such a function,
which is done herewith. I guess the developers among you find
the following self-explanatory - in a library delivery it
would be extensively commented.


typedef struct {
    unsigned short rawX;    
    unsigned short rawY;
    float          detX;
    float          detY;
    unsigned short PHA;
    unsigned short PI;
    unsigned short greyFilter;
    OBTime         obTime;
    double         ijdTime;
    unsigned int   status;
} JEMXevent;


With this struct one defines an event list as

JEMXevent *events=NULL;

and once it's allocated and filled can access information like in
these arbitrary examples

if (event[k].PHA > minPHA) { ... }

radiusFromCenter = sqrt( event[i].detX * event[i].detX + 
                         event[i].detY * event[i].detX );




int JEMXeventsGet(dal_element     *group,
		  Instrument      jemxInstrument,
		  JEMX_type       eventType,
		  ISDCLevel       level,
		  int             numGTIs,
		  OBTime          gtiStart,
		  OBTime          gtiStop,
		  const char*    *rowFilter,
		  JEMXevent     **events,
		  int             callingStatus);

This function would combine all the function calls needed to 
find the number of events, allocate a suitable buffer [this bends
CTS but so does, e.g. DAL3AUX] and read in all the columns
relevant for the given event type and level (RAW, PRP, COR).
I've kept the scheme currently in DAL3JEMX in that one passes
a list of GTIs read in before for selection, because I find it
very convenient.

  Please let me know how you think about this, writing the
whole function would cost me a few hours at most.

  Regards,
  Peter