Interactive

After executing the examples it is a good idea to gain some experience with the CURSE application. This can be done using the procedure INTERACTIVE. The procedure will plot a graph and then invoke the CURSE application, resulting in the following instructions being printed on the screen:

CURSE cursor options:
   Q - Quit.
   D - Draw to the cursor position.
   E - Expand the plotting limits.
   G - Calculate the gradient.
   L - Label the plot.
   M - Mark a point.
   O - Left justified annotation.
   P - Right justified annotation.
   S - Shrink the plotting limits.
   V - Move to the cursor position.
   X - Get the cursor position.
   Z - Zoom the plotting limits.

where the letter signifies the key that is to be pressed on the keyboard to achieve the desired effect.

If you have examined the example file for INTERACTIVE you will have seen that a label has been read in for each of the data points. It is now possible for you to use these labels by moving the cursor close to a plotted point and pressing O or P. When you do this, a label for the point nearest the cursor will be written at the cursor position. Do this for several points and then press Q to exit from the CURSE command. PONGO will have remembered the particular labelling that that you have performed and will then use the command WRITEI LABLST=YES to write the PONGO commands required to recreate these labels to a specified file. (You can use the procedure INTERACTIVE to explore the other functions of the CURSE application.)

The ZCOL area has been filled with the distances to each of the pulsars. These values can be used to plot points whose sizes are inversely proportional to distance (i.e. the closer pulsars are larger) by first taking the reciprocal of the ZCOL area with the CCMATH command:

PONGO> CCMATH Z=1/(Z+0.1)

and then the points plotted with the command:

PONGO> SIZEPLOT

Note here that a small positive value has been added to the distance data (i.e. Z+0.1) to avoid very large symbols for nearby pulsars.