ISPLINE will plot the spectrum in the "source" buffer and allow the user to fit a cubic spline to it based on knot points selected interactively with a cursor. The user is then shown the spline fit and allowed to interactively add or delete knot points to improve the fit. This routine does not work with 2-D images. With no keywords, the spectrum will be REPLACED by the spline fit.
ISPLINE will first plot the spectrum in the "source" buffer on the screen. By default, the spectrum is plotted as a line. It is possible to have the spectrum plotted as data bins (a so-called "histogram plot") by using the optional HIST keyword.
You will then be allowed to adjust the Y-axis limits with the cursor if the default scaling is not to your liking. To select the new Y-axis limits, place the cursor at the appropriate Y position with the arrow keys (no need to move the cursor in the X direction) and hit any key to mark the location. Upper and lower Y-axis limits may be marked in any order.
In all steps involving the interactive crosshair cursor, no distinction is made between upper and lower case letters, and there is no need to press the RETURN key. The (X,Y) position of the cursor is controlled by the four arrow keys above the keyboard.
ISPLINE will fit a cubic spline through a set of up to 60 (X,Y) "knot" points selected interactively by the user. There are three ways in which knot points may selected with the cursor:
DEFAULT or "AVG=n" keyword option:
To select a knot point, position the cursor at the desired X-axis location (no need to position in Y) with the arrow keys and hit the space bar or any key (except 'D' or 'X'). The knot point will be marked with a plus (+) on the spectrum.
You may delete the last knot point by hitting the "D" key (for "Delete"). All of the previous knot points may be deleted in reverse order of their selection by hitting "D" repeatedly. A deleted point is erased from the plot.
When you have finished entering knot points, hitting "X" (for "Exit") will fit the spline. The routine will automatically end knot point selection when 60 points have been chosen. Knot points do not need to be entered in strictly ascending order of X.
"XY" keyword option:
To select a knot point, move the crosshair to the desired (X,Y) position with the arrow keys and hit the "A" key (for "Add"). The knot point will be marked with a plus (+) on the spectrum.
To remove a knot point, place the crosshair over that point and hit the "D" key (for "Delete"). The offending knot point will be erased from the plot. Knot points may be deleted in any order.
When you have finished entering knot points, hitting "X" (for "Exit") will fit the spline. The routine will automatically end knot point selection when 60 points have been chosen. Knot points do not need to be entered in strictly ascending order of X.
The spline fit through the selected knot points will be plotted over the spectrum. At this point, you will be given the option of adding or deleting knot points if you are not happy with the fit.
To add a knot point, place the crosshair at the (X,Y) position where you want it to go and hit the "A" key (for "Add"). A plus (+) will mark this new knot point. Note that no averaging will be done despite the use of the "AVG=n" keyword.
To delete a knot point, place the crosshair over it and press the "D" key (for "Delete"). The offending point will erased from the plot.
When you are finished editing, hit the "X" key (for "Exit"). If you add enough points so that there are a total of 60 knot points selected (previous - deleted + added), the routine will automatically end editing.
The spline is then re-fit, and plotted as before. You may edit as many times as is needed to achieve the desired fit.
If two or more knot points are coincident in X-axis position, the routine will flag the offending points by circling them on the screen and ask you to use the cursor to remove at least one of them. To do this, position the cursor over the offending points and hit the 'D' key to delete one of them. Hitting 'X' will signal the program that you have finished removing all of the offending points. If more coincident points are detected by the routine, this step will be repeated until all such points are removed.
When a satisfactory spline fit has been achieved, there are 3 possible final results:
Examples:
NOTE:
To completely exit the program with no action taken on the spectrum, type a CTRL-Z in response to any Y/N prompt. This will return you to the VISTA command level.
WARNING:
Hitting keys (especially RETURN) while the cursor is in motion may occasionally have a pathological effect on the interactive cursor routines.
Also, avoid hitting control keys in cursor mode.
Only enter commands to mark or delete points, or exit the marking routines when the cursor is not moving.