I have uploaded to YouTube
most of the tutorials that show how to use the MeqBrowser. I did this
because the full-fledged tutorials are fairly large mpeg files. They
consume both a large amount of bandwidth and a fair amount of screen
real-estate when they are viewed. Of course, if you can, you are
encouraged to view the full-fledged tutorials on the Timba wiki page.
However, if you have difficulty with the full mpeg files, YouTube
provides a reasonable alternative. You do lose some screen resolution,
but things are still quite understandable.
The tutorials were all made with a linux program called xvidcap.
xvidcap worked reasonably well, but did have one or two problems.
Firstly, xvidcap tended to drop audio at the beginning of a broadcast,
so you may notice that the video begins in the middle of a sentence.
Secondly, xvidcap tended to crash when some `big'
activity started,
such as launching the meqserver (that's why I had to split the tutorial
on starting the browser and loading a file into it, into two separate
videos). Finally, xvidcap sometimes captures the screen in odd ways,
especially if we're dragging a widget into the area of the screen being
captured. Anyway, here you are ...
Our first tutorial shows you how to start up the MeqBrowser.
This
tutorial is short simply because xvidcap falls over when we start the
meqserver.
After
we pick ourselves up off the ground, the second tutorial (above)
continues on after we have launched a meqserver. It shows you how to
load a TDL script into the browser, and how the system compiles and
runs a simple script. Once we have loaded and run a script, we
are in a position to visualize the contents of nodes. Our third
tutorial describes some of the basic operations that can be done on a
visualization node such as zooming and getting a readout of data
values. Click on the selector below to view this tutorial.
There
are also tutorials that describe more specialized visualization
processes. Because a MeqTrees node can have data arrays with more than
two dimensions, extensions to the standard two-dimensional display
described in the above tutorial were developed.
The above tutorial shows you some of the capabilities for viewing data sets with more than two dimensions.
So
far we have demonstrated how MeqTrees visualizes real arrays. However
radio astronomers often have to work with complex-valued data
such as visibility data sets, telescope gains that vary as a function
of time, antenna voltage patterns etc. The following tutorial shows you
how one can visualize a complex-valued data set within the MeqTrees
browser.
While
the visualization nodes described above give you detailed information
about individual nodes, it may be important that get a complete
overview of the data in all nodes of a given type. This can be
done with the aid of a Collections Plotter. The Collections Plotter
essentially views the contents of a MeqComposer node; a MeqComposer
node can be used to gather into one VellSet the contents of many
children. The next tutorial demonstrates how we can use the Collections Plotter to view the contents of such a node.