For the European Space Agency's Herschel Observatory (scheduled
to be launched in 2007, http://astro.estec.esa.nl/FIRST/ )
the Interactive Analysis (IA) working group is in the process of
choosing existing plotting and math libraries/packages to use.
The existing Herschel and IA frame works mandate that software
developed by Herschel has to be in pure Java and free to the
Astronomical community. Lots of work has been put in for the
software making the IA and supporting the three onboard instruments.
In the end hundreds of man-years of software developing work
will likely be committed. I am not a spokes person for
Herschel IA but my work involves the plotting functionalities for the
SPIRE instrument onboard Herschel, and are making recommendation
and suggestions as which package to choose for IA. I speak for
myself.
When defining the IA frame work it is found desirable to have,
among many things, an elaborated data structure at some level that
supports units, scriptability (a jython console has been already
prototyped, much like VisAD's), easy plotting interface to the
end user etc.
I find VisAD to be quite promising. It is active, and fits into
the pure Java and "free" requirement easily. And it has the frame
work to visualize complex data. But there is some
distance from what it is now and what we want it to be. Currently
core VisAD has been made for 3D visualizations which the current
developers are most interested in. The plotting requirement of IA
emphasizes 2D X-Y style plots and 2D map style plots. It seems
that the astronomers are less enthusiastic about 3D visualization
than the spacephysicists and earthscientists.
I have some questions for VisAD. First of all I would like to
know from the VisAD developers whether they intend visAD to
become a more general purpose scientific visualization package.
This inevitably requires VisAD developers' time to help people
developing functionalities that these developers don't need
for their work.
For the more specific problems that I see, the single biggest issue
is the learning curve of using VisAD for both the end user and
the developer outside VisAD development group.
For the end user the VisAD python package has done some work to
hide VisAD complexity. For the developers who want
to use VisAD to do more than a few trivial tasks I have found
the complexity of VisAD to be formidable. I has been a frustrating
experience to try to understand the mechanics of VisAD from
reading the tutorials. When I tried to use VisAD to develop
something I often had to resort to reading the source code,
which I consider a bad sign -- the developer who wants to use
the package is forced to read the specific implementation
in the source code to guess the proper use of the API.
I am not the only person who feel this way. Most of my colleagues for
Herschel find VisAD's data structure difficult to deal with.
Herschel IA development team is big and geographically widely
distributed in many countries. Effective documentation is essential
for them. There is an IA working group looking for existing graphic
and math packages with some specific criteria. About VisAD the
conclusion is:
``Plotting a simple x-y plot can be done in several ways, yet it is
not
clear what the advantage is in doing it one way over another. The
documentation is not very helpful and the sample programs are not
very
illustrative. Though a library of static calls is provided for Jython
users, it seems to be very basic. The ?look and feel? of the
resulting plots is less than professional and there are no Jython
methods provided to quickly change graph attributes such as title,
labeling, scale, etc. A lot more work would be needed to provide full
interactive Jython functionality. The complicated data structures
would make this package hard to integrate with other packages (say,
for example, a numerical package).''
I am not convinced by the above conclusion. After I have got into
VisAD more,
I think the "difficult to use" problem is more a documentation issue
than structural.
I think what VisAD lacks for dealing with its complexity is 1)
wrapper
classes for casual users that doesn't demand much sophistication, to
"make simple tasks easy"; 2) better documentation for the outsider
developers to "make difficult tasks possible." More specifically, the
documentation should be all accessible from JavaDocs. The
documentation
of implementations should refer to the relevant design documentation.
I think if Herschel IA chooses VisAD, both Herschel and VisAD could
benefit on collaborated effort and complement each other to produce
a Java standard in scientific data visualization in general. There
are so much demand and wheel reinventing in scientific data
visualization
using Java on the net that I think a standard is a good thing.
Since most of my colleagues in Herschel have been turned away by
VisAD, I would like to hear what VisAD thinks about supporting
collaboration so I can convince them VisAD is desirable to use.
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