VOMegaPlot Client-The VOTable plotting utility (Version 1.0 Beta) |
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Introduction
VOMegaPlot Client-Server has been
developed for plotting different astronomical graphs using data stored in
VOTable format.
VOMegaPlot Server is hosting end of the VOMegaPlot Client-Server which handles
the requests made by VOMegaPlot Clients. When the Client sends the plotting
request, plotting of datasets happens at the server end, while only the plotted
image is transferred back to client. The basic concept
can be shown as:
About VOMegaPlot Client
VOMegaPlot Client has been developed as a part of the Virtual Observatory - India initiative by Persistent Systems and the Inter-University Centre for Astronomy and Astrophysics (IUCAA), in collaboration with Centre de Données astronomiques de Strasbourg (CDS).
Third Party Tools
- Ptplot 5.2, a 2D data plotter and histogram tool
implemented in Java. Ptplot has been developed at EECS department at the
- VOMegaPlot-Client makes use of cds.astro
(Astronomical coordinate manipulation) package for projection maps. The
package has been developed by CDS,
Top
Getting Started
For launching VOMegaPlot Client you can use,
-If the VOMegaPlot Server uses RMI:
java -jar VOMegaPlot_Client.jar [-host <server host
name>] [-rmiport <rmi port
number>]
where,
host is hostname / IP of
VOMegaPlot Server, the default value
is localhost
rmiport is RMI registry port
number on the server, the default value
is 1099
Example: java -jar VOMegaPlot_client.jar
-host vomserver.iucaa.ernet.in -rmiport 2000
-If the VOMegaPlot Server uses sockets:
java -jar VOMegaPlot_Client.jar -usesockets [-host
<host name>] [-port <port number>]
where,
usesockets is used if communication between server and client is to
be done at socket level.
host is hostname / IP of
VOMegaPlot Server, the default value
is localhost
port is the port number on which
server listens, the default value is
2020
Also,
[] indicates that the argument is optional.
Example: java -jar VOMegaPlot_client.jar
-host vomserver.iucaa.ernet.in -port 80
and then the VOTable can be loaded by choosing the corresponding voi file with the help of 'File->Open VOTable' menu.
Note: To run VOMegaPlot Client, you must have JRE 1.4.2 or higher installed. To see the version of JRE installed, type the following command at the command prompt:
java -version
Figure 0
Plotting Scatter Plots
To draw a plot of one columns against the other,
- Select the column to be plotted on the X-axis.
- Select the column to be plotted on the Y-axis.
- Click "Plot" button.
You can see the scatter plot. If required, you can plot data points on a log scale by setting the option appropriately using the "Log" checkbox. Also, by checking the "Rev" checkbox, the data points are plotted on a reverse scale.
Figure 1
Clear Plot
To clear all the selection on the plot, click on the
"Clear plot" icon represented by 
.
Changing Plot properties
To change the plot properties
click on the properties icon 
in the panel to the right of the plot. This
opens the "Set Plot format" dialog as shown in Figure 2.
For changing properties such as title, labels ranges etc., click on the "simple" tab.
Figure 2
For changing properties like color and marker style click on the "Advanced" tab.
For changing marker style for all datasets click “Select marker style and color for ALL datasets”.
For changing marker style or color of single dataset click “Select marker style and color for a dataset”.
You can choose various marker styles such as "pixels", "points" etc. Setting the marker style to "various" allows plotting with different symbols like triangle, rectangle etc.
Figure 3
The default color chooser provides three chooser panels, one of the panels is
shown in Figure 4.
Figure 4
Loading Multiple VOTables
To Load mutiple VOTables click on the "File -> Open VOTable" menu. The new VOTable is plotted now.
Zooming
For zooming into the plot you need to be in the Zoom mode. To go in zoom mode, choose "Zoom" from "Mode" combo box at the bottom of the panel to the right of the plot.
To zoom in, drag the left mouse button down and to
the right to draw a box around an area that you want to see in detail. To zoom
out, drag the left mouse button up and to the left. To get the
original graph click on the "
.
Overlaying Plots
To overlay plots (simultaneously viewing multiple plots with similar range on the same axes system)
- Select column to be plotted on the X-axis.
- Select column to be plotted on the Y-axis.
- Click "Plot" button.
- Select column to be plotted on X-axis (represents another plot).
- Select column to be plotted on Y-axis (represents another plot)
- Set the "Overlay" option.
- Click "Plot" button.
Note: If you want to overlay x, y columns of
one VOTable on x, y columns of another VOTable select the VOTable from the
VOTable Combo Box on the right of plot. (If there are multiples resources in a
VOTable or multiple tables in a resource, use the Resource and Table combo
boxes in order to select another resource or table before choosing x, y
columns).
With overlaid plots, legends are added on the right hand side. Each one of the VOTable, Resource and Table combo boxes display an index along with the name of the VOTable, Resource or Table. The index is displayed within curly brackets {} in each of the combo boxes. The indexes are combined together along with the column name to form a legend.
Figure 5
Histogram Plot
To launch histogram window click on “View -> Histogram
Plot” menu or the “Histogram” button
.
Figure 6
To draw the histogram of a column
- Click "Histogram" button .
- On the popped up histogram, select the column for which histogram is to be plotted and click on the Plot button.
A sample histogram is shown in Figure 7.
Figure 7
If you want to plot the histogram of data points on a log scale, then check the "Log" checkbox corresponding to the X-axis.
Changing Histogram properties
To change the histogram
properties click on the button.
Click on the "Simple" tab to change properties like the bin width, X Label, Y Label,
X range, etc.
Figure 8
Click on the "Advanced" tab to change the color of the histogram.
Figure 9
The color panel provides facility to select color using swatches, hue saturation brightness (HSB) color model and red green blue (RGB) color model.
Overlaying Histograms
To overlay histograms (simultaneously viewing multiple histograms with similar range)
- Select column to be plotted on the X-axis.
- Click "Plot" button.
- Select column to be plotted on X-axis (represents another plot)
- Set the "Overlay" option.
- Click "Plot" button.
Example of overlaid histogram is shown in Figure 10.
Figure 10
Density Plot
The density plot is made up of a grid which comprises of 10000 (100 X 100) cells. Two parameters namely, cell density and total count are displayed to help understand the distribution of data points. Both these parameters are associated with a specific color shade. Cell density indicates number of points (range) that lie within one cell. Whereas the total count indicates total number of points that have been assigned a specific color shade.
A sample density plot is shown below.
To view the density plot corresponding
to the scatter plot, click on the density plot icon 
in the panel to the right of the plot.
Figure 11
Projection Plot
The stars on the celestial sphere are like cities on the globe. While a globe is the most accurate representation of geography, it is difficult to carry around. We have invented flat representations of the globe that, although they distort shapes, areas, and directions are a whole lot easier to carry around. Projections are mappings from this 3D space to a 2D space.
RA, DEC columns are needed for projection plot. For setting
of these columns, you will be prompted with a dialog to select the RA and DEC
columns when the projection plot window opens.
The projection plot for the data
plotted in VOMegaPlot Client can be seen by clicking on projection plot icon 
on the panel to the right of the plot.
For every VOTable loaded in VOMegaPlot Client there will be a corresponding dataset in the projection plot.
The following 3 types of Projections are provided:
- Sinusoidal/Sanson Projection
- Aitoff/Hammer Projection
- Mollweide Projection
Changing the type of Projection:
The projection type change can be changed by selecting the projection type from the
"Projection type" combo box from the projection plot dialog.
Changing the Center
of Projection
The center of projection is the coordinates of the center point of the projected sphere. We
can see the projected points from different positions such as "Standard", "North Pole"
and "South Pole" by changing the center of projection.
The center of projection can be changed by selecting the center type from the "Center"
combo box.
After selecting the required options in both the combo boxes, you can view the desired Projection plot by clicking the plot button on the Projection Dialog.
Sinusoidal Projection Plot for ‘First’ catalog is shown in Figure 12:
Figure 12
Feedback Address
We would be happy to receive any feedback/comments on VOMegaPlot. For feedback and comments please contact voindia@vo.iucaa.ernet.in.