VOMegaPlot

[Ajit Kembhavi]

Dear Friends,

We at VO-I have developed a package to plot a large number of points.  A 
brief description is given below.  We would soon be releasing a beta 
version,a nd would be very grateful if you try out the plotter, and let us 
have your comments, since we expect that significant improvements will be 
needed.

We will be releasing the source code of VOPlot before Christmas.

With kind regards,

Ajit Kembhavi

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VOPlot and VOMegaPlot
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VOPlot is a tool developed for graphical representation of two and three 
dimensional data. It is based on PTPlot 5.2, which is a 2D data plotter 
and histogram tool implemented in Java. We have found that VOPlot works 
well for plotting upto several tens of thousands of points, after which 
the response can be slow. In VOPlot, when a user loads a VOTable xml file, 
it is first parsed and the data so obtained is stored entirely in memory. 
The in-memory data is subsequently used for plotting or performing 
calculations and analysis. This approach does not work while plotting a 
very large number (millions) of points, as the amount of memory required 
for storing all the points goes beyond the memory allocated to the VOPlot 
by JVM (Java Virtual Machine). Increasing the memory allocation is not 
possible in all cases, as there are always large VOTables which require 
more memory than what is available.

VOMegaPlot has been developed to address tables with very large numbers of 
points in them. The approach adopted is to store the data present in a 
VOTable xml file into data structures, which are serialized on the disk in 
a plot-friendly format. During the actual plotting operation, only the 
relevant data necessary for plotting is loaded. This significantly reduces 
the memory requirements and allows plotting of large VOTables. When 
VOMegaPlot is to be used with a very large catalogue, the catalogue has to 
be processed to produce a series of files using a straightforward 
procedure which is provided. This is to be done just once for a given 
VOTable, and the plotter uses the whole set of files when it is invoked 
subsequently.

VOMegaPlot presently has a a limited number of the features of VOPlot, and 
we hope to expand its scope further in the future. We are making an early 
release to the community so that we receive comments and suggestions from 
potential users. Please send your comments to 
nilesh_urunkar at persistent.co.in, with a copy to shaikh at iucaa.ernet.in.



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