VOMegaPlot

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

VOPlot and VOMegaPlot

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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