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5.2. Graphic

A graphic is an XY plot where one or more signals are represented as a function of time or frequency. When only one signal is represented, the Y scale is the signal amplitude (count or volts). When various signals are shown (see figure 1), the Y scale ranges from 0.5 to n+0.5 where n is the number of signals. The axis label are generally replaced by the names of signals suffixed by the signal's component. The baseline (reference line with a null amplitude) of each signal is located at y=1, 2,..., n. The signals are drawn around their baseline. The maximum amplitude around this baseline is adjusted by the normalisation parameters described hereafter.

Areas of a graphic

Figure 1: Graphic viewer, definition of areas: red = graphic's background,
yellow = Y axis, green = X axis, and blue = graphic's content.

The graphic viewer makes use of a general XY plot object from the scifigs library. More information about it can be found in the scifigs documentation. scifigs offers highly configurable XY plots which can be saved and restored easily. Usually, figures are exported to bitmap formats like jpeg or png, or as postscripts or pdf. In this case, any modification of the aspect (fonts, scales, ticks, ranges, ...) require the original program to be re-run. One of the reason for changing the aspect would be to provide a figure on two kinds of supports: a printed book and a slide presentation for instance. With scifigs, you can save the aspects and the data with their real scales (files ".mkup" and ".layer", respectively). figue, is an external program released with scifigs library, that allows you to construct complex figures from these files grabbed here and there from programs linked with scifigs (like geopsy).

A graphic is divided into four distinct areas.

Graphic's context menu

Figure 2: Context menus for graphic: (a) graphic's background,
(b) graphic's content, and (c) axis.

The graphic's contents is itself divided in layers. Various types of layer have been developed to plot curves, points, grids, ... Signals are plotted in a special type of layer developed especially for geopsy. Only the parameters linked to this layer are discussed here.

In each area, a particular context menu (mouse right button, figure 2) is available to control the object. In each area, a double-click is equivalent to "Properties" in menus in figure 2. CTRL+m is equivalent to a right click in the graphic's background (red zone). This feature is useful when the background is not visible, i.e. when axis are hidden.

The make-up is the set of parameters that describe the aspect of the graphic, modified by the means of "Properties" in each specific area. You can save the current set or restore an existing one ("Save make-up" or "Restore make-up", figure 2(a)). In a similar way, the data contained in the visible layers of the graphic's contents can be saved to or restore from a file ".layer" (figure 2(b)). Note that ".layer" files need complementary files named ".layer.bin" which contained binary data. Do not separate these files when moving or copying to other locations.

Note: the export of the layer developed for signals as ".layer" is currently not implemented. To avoid space consumption on disk, the complete geopsy core should be used in figue, which is more complex than other standard layers. A bitmap layer might be an alternative. However, you are free to import other types of layers in graphic viewer for comparison purposes (e.g. a segmented line representing travel-times estimated elsewhere). Currently, to export the signals to a figure, adjust the axis to their final sizes, set a resolution compatible with your final medium (e.g. 300 or 600 dpi for a laser printer, 72 to 100 dpi for screen or web publication) and export the graphic as bitmap (png or jpeg).

SignalDisplay Layer: signal properties

You can change the appearance of the signal layer by selecting "Properties" from the context menu of the graphic's contents, or double-click in the graphic's contents (blue area in figure 1). Switch to tab "Signals", a dialog box like the one shown in figure 3 will let you edit the current properties.

Signal properties

Figure 3: Signal properties.

On the left, "Type" box lets you select the features you want for plotting signals.

The right part contained the normalisation parameters:

The procedure remains valid when only one signal is plotted, except that "max of each" or "max of all" have no effects. An example of signals normalised by "visible max of each trace", clipped at 25%, and with an overlap of 4 is given in figure 3.

Signal normalisation, clipping and overlapping

Figure 3: Signal normalisation, clipping and overlapping.

The y of the baselines may also be calculated according to the receiver positions ("Use receiver coordinates"). An horizontal line is automatically adjusted to the receiver X,Y coordinates with a least square method. The receivers coordinates are then projected on to this line to calculate distances along this line. The scale of the Y axis is the distance along this line.

For colour representation of signals, the values of the colour palette can be adjusted by clicking on "Default values for colour palette". The normalisation and the clipping settings are taken into account.

The display settings are saved in file "$HOME/.qt/geopsyrc" under the rubric "DialogOptions", entries "Signalgcprop/*" (for Linux users). For Windows users, this information is located in the registry (regedt32). The settings are automatically saved when the properties of the graphic's contents are edited. The saved settings are restored only each time a new graphic viewer is created.

SignalDisplay Layer: picking

Picks are time markers that you can use to identify particular times (e.g. Vp arrivals for refraction, time limits for signal processing such as a time domain taper). There are 10 distinct time picks you can use. You can change select the visible time picks as well as their colours with the tab "Pick" in the graphic's contents properties (figure 4). These parameters are saved and restored in the same way as other settings.

Signal picks

Figure 4: Signal picks, visibility and colours.

You can modify picks in a table by editing the corresponding fields. However, it is usually edited in a graphic viewer with mouse clicks. As shown in figure 2(b), select menu "Pick" from the graphic's contents menu. You will be prompted to select one of the ten picks to edit.

In certain circumstances, it may be useful to magnify the signal around the picks, select "Magnifier window" to display a signal signal viewer with a zoomed time scale. It is a usual graphic viewer, with a vertical line to mark the current position of the mouse (created with ParallelBands layer, hence you can hide it if you want). All the common properties of a graphic viewer may be changed, for instance to enlarge the time interval or to fix the Y scale. The X interval is kept constant as the mouse moves.

The active trace is highlighted in red and the current pick number is displayed in the bottom right corner. If "Picking disabled" is displayed, it is likely that you are in "Zooming" or "Editing" mode (displayed in bottom left corner). In this case, the clicks will not have any effects. First you have to quit this mode by hitting CTRL+SHIFT+z or by selecting "Zoom" in the context menu (figure 2(b)). Once "Setting pick n" is displayed, any click on the mouse left button will modify the value of the current pick. Use the "Up" and "Down" arrows to change the active signal, "Left" and "Right" arrows to switch to other picks. If hitting those keys has no effect, check that the main graphic viewer is active, if not click in its title bar (this is frequently the case when a magnifier is used).

Y axis: zoom blocked

By default, the minimum and the maximum visible limits of the Y axis are fixed. You cannot change them with the zoom (figure 2(b)). You can still change them by editing the axis properties (min and max). The blocked zoom lets zoom in the signals with a rectangle which Y limits are ignored. Only the X interval (the time or the frequency) is taken into account. You can unlock this feature by unchecking the option "Zoom blocked" in tab "General" of the Y axis properties dialog box. This feature may be manually set for X axis but it is less useful.

Signal selection

Contrary to tables, it is not possible to select particular signals in a graphic viewer. The drag and drop mechanism works in a similar way but all the signals are considered rather than a selection. Graphic viewers also accept drops of signals that are added at the end.

Time or frequency spectra

If the signals to plot are all of the same TYPE, the X scale is adjusted automatically (time or frequency). It may append that the signals are not of the same type, in this case, the X title is set as "Time or Frequency". Usually, the orders of magnitude of the X axis for time and frequency are quite different, hence the plot is partially unreadable. To recover signals, either as time series or frequency, select either "FFT/Time" or "FFT/Frequency" from menu "Waveform". If the signals are zoomed in (marked by scroll bars along X and Y axis), and if you transform time series into spectra and vice-versa, it is likely that the current zoom rectangle will not be adequate for the new X scale. Thus, it is better to unzoom (or CTRL+-), until the scroll bars disappear, before or after a FFT transformation.