A brief phone meeting was held between Paul Nord, Jim Musser and
Maher Quraan on July 5, 2000 to discuss event display.  The
following is a summary of some of the items discussed at that meeting.

Paul Nord created the current version of event display well in advance
of the development of pattern recognition and track fitting.  It is
a powerful tool, but he has been waiting for the rest of the code to
catch
up, in order to know what further requirements there might be.

What we expect to be able to display is the following:
(Most of these are already built into Paul's code.)

        -wires
                Already a part of the standard display
        -points
                Implemented as a "Hit" - a box around some point in
space with
                a dx, dy, and dz.
        -lines
                Implemented as a "Track" - a set of 2 or more points
        -circles
                If constructed as a Track with at least ~80 points per
rotation
                they look very good on the display.

                Could also implement a circular "Hit" drawn as a disk
with a dz
                and radius in xy.
        -helices
                Paul still recomends using the "Track" and constructing
the set
                of xyz points from the fortran routines.  The
abstraction of
                converting from helix parameters to xyz coordinates
needs to
                be done in fortran so that the collaboration can
validate it.
                The actual track may be very complex since helix
paramters
                might change at each plane due to energy loss or hard
scatter.
                This could be made a part of the display, but the
display would
                call a fortran routine to construct points.
        -titles
                All hits, tracks, wires can have text titles associated
with
                them.  These can be displayed by moving the mouse over
the
                element.  In addition, there is an event title displayed
at the
                top of the screen.


a few overlapping displays in different colors
        Tracks can be displayed in a variety of colors.
        Will add this feature to Hits as well.


We expect to be able to display these:

        -from top, bottom, end views, or partially rotated views

        -limited to a subset of the detector (i.e. half detector,
         single plane, or limited range in Z)


We expect to be able to select data to display from anywhere in the code
for
the purpose of development and debugging.  Currently the only place we
can
display things (that is, call functions which will add elements to the
display)
is from the PHOTO.f90 and USER_PHOTO.f90 routines.  We can do some
simple
changes to the sturcture of ANALYSIS and other routines to allow
function calls
from other places (e.g. when the display gets initialiazed and when the
previous event gets cleared and the next setup.)

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