Closing in on your spectrum; interactive vs non-interactive modes

 If you are in interactive mode, there are quite a few things you can do with the spectrum on the screen. The first thing is zoom in on a small section of it so that you don't have to look at the parts you can't explain. There are two ways to do this, both of them easy.

The quick way is to use the mouse cursor (using Xwindows) or the cross-hairs (if you are working with a VTxxx graphics-compatible terminal) to make a box around the part you want to look at more closely. Point the mouse cursor at the position on the Xwindow plot screen, and type a command. If you're using a VTxxx terminal you use the arrow keys to move the crosshairs around; holding down the Shift key makes the lines move in large steps. Place the cursor position (or intersection of the cross-hairs) on one corner of the box you want to draw and hit one of the following keys to mark the spot; t, b, l, r. For example, to identify the lower right corner of the box you hit b (for `bottom') and r (for `right'). Now go to the opposite corner and hit the other two keys (i.e. t for top and l for left). The box will not appear on the screen until you hit d for draw. This will draw the box on the screen. If you made a mistake drawing the box just try again. When you've got the box you want hit n for new_limits and the portion of the spectrum inside the box will be replotted. Table  (taken from Rachael Padman's SPECX manual version 6.3) shows other possibilities; I'm sure the options have increased in number since then, so use the h option (for `help') to see a complete list.

 

Key Mnemonic Function

H HELP Produces a list of all valid options

? QUERY Tells you the current coordinates of the cursor

L LEFT Define the left-hand boundary of the current 'box'

R RIGHT Define the right-hand boundary of the current box

T TOP Define the top boundary of the current box

B BOTTOM Define the bottom boundary of the current box

D DRAW Draw the current box

C CLEAR Erase the alpha (ASCII) screen

Q QUIT Leave interactive graphics

E END Leave interactive graphics, erase graphics screen

N NEW_LIMITS

S LIMITS Lets you set new plot limits by hand

A ACCEPT Tell the program to accept the current box

+ MARK Mark position using cross-hair

<CR> RETURN Accept default box (for input of baseline regions)

 

If you want exact limits on the axes you can use the second method. First figure out what the x and y limits are from your plot. Lets say, for example that you want the x axis to run from -50 to +50 km/s and the y axis from -5 to 50 Kelvin. You would use the set-plot-scales command:

>> set-plot-scales
Do you want automatic scaling of X-axis? (Y/N) [Y] n
X-axis scale: Beginning and end? [ 150.00  300.00] -50 50
Do you want automatic scaling of Y-axis? (Y/N) [Y] n
Y-axis scale: Beginning and end? [ -10.00   10.00] -5 50
..

If you want to see all of the spectrum again then send the following;

>> s-p-sc
Do you want automatic scaling of X-axis? (Y/N) [N] y
Do you want automatic scaling of Y-axis? (Y/N) [N] y

Note that you can set either of the x and y scales to automatic scaling, or both. This is a very useful feature.