The Graphics menu provides methods for drawing text and a range of figures on the plot. This allows you to add annotations, but also provides the basis for the interactive graphics used by the various toolboxes.
To draw a figure on a plot you need to select an option from the Drawing mode sub-menu and then, depending on the figure type, either drag out a region or select fiducial points. When creating a figure using points these are completed using a double click on the last point.
In the Drawing mode menu the currently available figure types are:
- a straight line,
- a rectangle,
- an ellipse,
- a poly line (last point not connected to first),
- a polygon (last point connected to first),
- freehand curve,
- a text string,
- an interpolated curve (splines and special spectral shapes),
- a rectangle which only moves along X (indicates a range of coordinates).
There are also two special modes:
When the mode is select (this is usually the default state), clicking on a figure selects it. You can then drag it around to move it, or drag one of the grips (the little squares) to change the shape. To select more than one figure you hold down the <Shift> while clicking.
- select figure,
- edit figure.
The edit mode can be used to add new points to a polyline, polygon or interpolated curve. Just select this, click on the figure you want to edit and then start adding new points. You can also edit text strings, just choose the edit mode and click on the text, this produces a dialogue with the text for editing.
To change the properties of a figure (line width, fill/outline colour, font etc.) just select the figure and then choose the option you want to change from the various menus. You can define these before creating a figure too.
Interpolated curves are like polylines in that they are defined by a series of points, but they can only have increasing or decreasing X coordinates (so cannot double back on themselves). They are intended for drawing figures that are related to spectra, specifically spectral backgrounds and lines. In fact if you draw an interpolated curve you can convert it into a spectrum for removing from a real spectrum using the Generate spectra from interpolated lines toolbox. The types of interpolation scheme available are:
- Hermite, interpolation based on Hermite polynomials. The effect is supposed to construct reasonable analytic curves through discrete data points (i.e. like those a human would produce).
- Akima, interpolation based on Akima splines. Like Hermite this supposed to construct human-like analytic curves.
- Cubic, interpolation using natural cubic splines.
- Polynomial, interpolation using a simple polynomial of order one less than the current number of points.
- Linear, interpolation using straight-lines (like polyline, except it has sorted X coordinates).
- Gaussian, interpolation using a Gaussian line-profile. This can only have four reference positions (and is initialised from the first two indicated on the plot), these define the left extent, width, height/centre and right extent. The order will switch if these are dragged past each other (so dragging the width grip beyond the left extent grip will switch their meaning).
- Lorentz, interpolation using a Lorentzian line-profile. Works like the Gaussian curve.
- Voigt, interpolation using a Voigt line-profile. This also works like the Gaussian curve, but has five characteristic positions, left extent, Gaussian width, height/centre, Lorentzian width, right extent.
Once you have created your figures you may want to save them for restoration at a later time, this can be done using the Graphics->Save/restore figures dialogue. Figures are saved using the physical coordinates of the spectrum, so should be re-drawn at the correct wavelengths etc. on new plots.