Figure 2.2: The Model Editing Tool.
The main window is the model editing tool (Figure 2.2). The main part of the tool is taken up by a scale diagram of the current model. The different types of components are represented by different glyphs: points are small red crosses, optically-thin spheres are green circles with magenta edges and elliptical Gaussian brightness distributions are blue ellipses with yellow edges and yellow lines marking the axes of the ellipse. This area will initially be empty apart from a reference grid of white lines on a black background. You will see a menu bar above the diagram and a message area below it.
Unless you have set the application resources to override the program defaults (see Chapter 3) the model editor will use a scale of 1 milliarcsecond to 1 centimeter and the lines in the reference grid will be spaced 1 milliarcsecond apart. You can change both the scale and the grid spacing using commands from the View menu. This menu also contains a toggle button that controls the display of the reference grid.
You will create the model by using commands from the Edit menu and by manipulating the glyphs representing the model components in the editing area.