Tony Willis's MeqTrees Video Tutorial Page


This page assembles a number of video tutorials on various topics related to MeqTrees. Hopefully the tutorials will provide some insight into the concepts behind MeqTrees, how to set up a MeqTrees script, and various aspects of working with the MeqBrowser. If nothing else, viewing these video tutorials may help people who suffer from insomnia!

The Measurement Equation tutorial gives a gentle introduction to some of the concepts behind the Measurement Equation. It describes why use of the Measurement Equation should lead to better calibration of an observation made with an aperture synthesis telescope.

After you have viewed the Measurement Equation tutorial, you may wish to go to sleep. If you are a glutton for punishment, you may continue on to the MeqTrees Introduction. This tutorial describes some of the basic concepts behind MeqTrees and how how these ideas lead to powerful, yet relatively easy, procedures for implementing the Measurement Equation.

The first two tutorials give general overviews of the Measurement Equation and MeqTrees. We now start to investigate some of the practical issues of implementing and running MeqTrees scripts.  



The above figure shows a simple tree.  A request percolates down from the `Request Domain' to the leaves of the tree (the MeqFreq, MeqTime and Meqparm nodes).  Results are then returned back up the tree. More details of this tree are given in the MeqTrees wiki and in the  Script Tutorial. This introductory tutorial looks at a simple MeqTrees script that creates and processes the above tree. It describes the various sections of the script, what order they are processed by the MeqTrees browser, and how a tree is executed.  Then the first Browser Introduction shows how you start up the MeqTrees browser. Next, the  second Browser Introduction shows you how to load the file described in the Script Tutorial, and execute the script.  The browser provides extensive capabilities to visualize the contents of individual nodes in a tree.  The Visualization Introduction continues from the point the Browser Introduction finished to show you some of the visualization capabilities of the browser display.

There are several tutorials which go into a more detailed discussion of the visualization abilities of the browser. Since MeqTrees mostly deals with the calibration and simulation of aperture synthesis telescopes, we will often want to look at the UV plane complex-valued visibility data that is either observed by a telescope or predicted by a sky model. The Complex Data Visualization tutorial shows you the features for viewing visibility data in the MeqTrees browser.  While visibility data is basically two-dimensional, usually being a function of time and frequency, it is not uncommon for MeqTrees nodes, especially those which deal with the effects of E-Jones (antenna voltage pattern) matrices, to have data sets whose dimensionality may be greater than two. A voltage pattern, for example, may be a function of time, frequency, and L and M, the direction cosines on the sky. The N-Dimensional Visualization tutorial will show you how you can visualize data sets whose dimensionality is greater than two.