Tutorial Contents

Chart view

Format

Episodic data

Gain and position

Data scaling

Timebase viewport

Cursors

Markers, Annotations

Scale bars

Multiple views

High-quality figures

Clipboard

Contents

Chart view

The chart view
The chart view window.

Trace and View Format

Data traces are numbered in sequence (1 – n, with a maximum of 128). The number is the ID of the trace. By default, each data trace displays in a particular colour on a separate axis, and optionally has a label associated with it. Each axis also has a label associated with it. These features can be edited.

You can hide or show the display grid, the trace IDs and labels and the axes using commands on the View menu.  You can set the height and width of the display to particular values (in pixels) with the View: Set size command. This may be useful if you want to copy bitmap images of the display with known fixed dimensions.

Line width

By default all traces show with a line width of just one pixel. However, when exporting images for display in other programs this can lead to rather faint traces. You can increase the display line width if desired.

Dot or Line display

Normally, each datum point within a trace is joined to adjacent points by a straight line. However, if you want to see the exact sample times and values, you can disable the line, so that each point just draws as a dot.

The menu option acts as a global command: all traces display either with lines or dots. If you want to set this option on a trace-by-trace basis, use the Traces: Format menu command to display the Trace format dialog box, and check or uncheck the Dots option for each trace.

Inactive data sections

Some commercial formats, and some data manipulations within DataView, produce traces with sections of inactive data where values are not defined (e.g. the recorder was temporarilly switched off). Such sections are displayed as grey, zero-valued data by default, but can be hidden altogether by toggling the View: Show inactive data sections command.

Data display area

By default, the axes are evenly spread across the vertical height of the view. However, you may want to keep part of the view clear of trace data in order to display events (see below) or annotations.

You can still place traces in the upper portion by adjusting their position (see below), but trace data can conveniently be restricted to within axis limits, and hence the lower portion of the view, by using Autoscale on all axes. If you set the Data display area to 0% then all data traces are hidden, although they are of course still present in the file and can be revealed by choosing a non-zero display area.

Time units

The View: Main display time units menu allows you to set the time units of the main display to milliseconds (the default), seconds or decimal minutes (i.e. 1.5 minutes means 1 minute 30 seconds). Different views (see below) of the same file can use different time units, so you can view large sections of a long file using time units of minutes, while simultaneously focussing in on individual spikes using a second view with millisecond time units.

Episodic data

Data can be episodic. In episodic recordings the time-base is not continuous but rather contains episodes of data recorded sequentially in time, but with arbitrary gaps between each episode. Event channel a acts as a marker, with each event indicating the start of a new recording episode. Data can be converted between episodic and non-episodic with the Transform: Episodes menu group. The difference is in whether events in channel a are treated as episode boundary flags, or just normal events.

It may be important to flag episodic recordings correctly because certain analysis and transform procedures need to restart at episode boundaries due to discontinuities in the data waveform.

Trace Gain and Position

You can adjust the gain and/or position of traces by several methods:

Selecting Axes and Using the Toolbar

Selected axes have their axis labels written in bold type, while non-selected axis labels are written in grey type.

If you hold down the control key as you click one of these buttons, then the effect is applied to all traces, not just those on selected axes.

Keyboard shortcuts

The following keyboard shortcuts work on the selected trace:

  Autoscale control 0 (zero)
  Increase gain + (plus)
  Decrease gain - (minus, hyphen)
  Trace up/down up/down arrow keys

Data scaling

When DataView reads from a file, it assumes that all voltage values are in units of millivolts, or converts them to this if the file itself contains appropriate scaling information. However, it sometimes happens that numbers from external files are stored in other units without any explicit scaling information. In this case Dataview can scale individual traces as they are read from file.

Imagine that trace 1 of the example file came from a signal generator that produced a sine wave with a peak-to-peak amplitude of 0.1 mV, but that it had been passed through a x10 amplifier before it was recorded. The values in the file would thus be 10 times greater than the real signal.

The amplitude of trace 1 has now been reduced by a factor of 10.

Of course, the same scaling procedure can be used even if the original signal represented some factor other than voltage, such as force, or current.

Viewport

The viewport is the section of the total recording that is visible in the chart view. This depends on the display timebase and the display start time.

The grey slider bar under the X axis shows the viewport as a fraction of the total record, where the full width of the axis represents the whole record.

You can adjust the viewport by several methods:

Time vs samples

The first sample point in the viewport displays on the extreme left, while the last sample displays on the extreme right. The viewport time values specify the time between the first and last visible sample, i.e. the summed duration of the gaps between the first and last visible samples. There is therefore one more visible sample than there are gaps.

There are 9 dots visible spaced at 1 msec intervals, hence 8 gaps. The start time is 0, and so the end time of 8 msec fits with the data display.

Toolbar navigation commands

Commands associated with navigation are on the Navigation menu (not surprisingly). The most useful commands are also duplicated as toolbar buttons.

Keyboard shortcuts

  Compress /
  Increase gain *
  Left/right page control left/right arrow keys
  Left/right page % left/right arrow keys
  Show all alt 0
  1 : 1 (one sample per pixel) alt 1
  Go to start Home
  Go to end End

Expand Compress Focus

When you change the timebase you can determine whether the expansion/compression is centered around the left-hand edge or the mid-time of the display using the Navigation: Focus left edge (else mid) toggle command. This command is global; it effects navigation in all open windows.

Cursors

You can position any number of vertical and horizontal cursors on the screen. Cursors are used to make quick measurements of data, and to demarcate sections of data for various analysis procedures. Cursors are not persistent (they are not stored with the data file), and cursors in each view are independent of each other. Cursors do NOT move with the data, so if you pan the data, the cursor stays in the same screen location.

Cursors are controlled through the Cursors menu.

Shortcuts:

Press the keyboard 'v' key to add a vertical cursor to the centre of the view.
Press the keyboard 'h' key to add a horizotal cursor to the centre of the view.

Further details about cursors are given here.

Markers and annotations

Markers

Markers are labelled tags that are associated with a particular time within the file, but not with any particular trace.

Try adding several markers at different points in the file.

Annotations

Annotations are like markers in that they display at particular times, but are unlike markers in that each is associated with a particular trace and data values, so they move their vertical position if the trace position moves.

Try adding an annotation with some text, and then change the position of the associated trace to see the annotation move.

Locking markers and annotations

Both markers and annotations can be independently locked to prevent them being accidentally moved by the mouse.

Some commercial acquisition formats (e.g. CED Spike files) use markers to indicate particular points of interest in the record. These are imported into DataView when the file is read, and such markers are automatically locked. Markers and annotations can be unlocked by unchecking the command above.

Scale Bars

You can add a horizontal (timebase) scale bar, and multiple vertical (amplitude) scale bars to the view. These will show even if the axes are hidden (see the View: Show axes menu command).

The main point of these scale bars is that they are included when the screen display is copied to the clipboard, or when vector format files are exported using the File: Write hi-def graphics commands (see below). This means that if these files are subsequently edited in graphics programs and the traces are scaled by stretching or compressing, then if the scale bars are included in the transform so that there is a continuous record of the scales that can be included in publication-quality figures.

Vertical scale bars are added by a similar process, but for these you also have to specify which trace the bar applies to. The bar will then change its height if the gain of that trace is changed. You can add multiple vertical scale bars if necessary

Scale bars can be hidden or shown in the main view using the View: Show scalebars  command.

Multiple Views

You can have multiple views of the same file open at the same time. Select the Window: New window command, and a second view opens. This view shows the same data as the first view, but has independent trace format, gain and timebase settings. With this facility you can switch between looking at the whole data file to get an overview, and looking at a particular part of the file in detail, simply by switching views (remember pressing control + tab is a standard Windows shortcut for this). When you save a file, it is the display settings of the currently-active view that get saved and which will load as the default when next you view the file.

Note that the File: Close menu command will close all open views of a particular file. If you click the standard Windows X at the top-right of the view title bar, you will only close that view.

High quality figures

If you want to obtain high-quality copies of the data for incorporating into figures for publication, the File: Write hi-def graphics commands give you several options. Probably the most flexible choice is to write the file in vector EPS (encapsulated postscript) or SVG (scalable vector graphics) format, since most vector graphics programs can read one or both of these formatsPowerpoint used to be able to read EPS but not SVG format, but the version in Office 365 can read SVG but not EPS format..

You will be asked to specify the width of the image (in inches or mm), and the resolution (in dpi: dots per inch) of the target printer. The data and event traces, and any visible markers and annotations, are written in the same relative positions that they have in the screen display. Note that no text, gridlines, cursors or axis scales are written to the file. This is a design decision based on the fact that you will probably further edit the image to produce a publication quality figure, and will probably want to add text labels and annotations specific to your own purpose. Also note that you can add scale bars to the file which can be manipulated within the graphics program along with the traces to which they apply. In this way publication-quality scale bars can be incorporated and maintained right from the outset of figure construction. See Scale bars above.

A legacy option retained for backwards compatibility is to export the data in HPGL (Hewlett-Packard graphics language) format. The HPGL file contains a copy of the data traces displayed on the screen in HPGL format, with a horizontal resolution of 8000 pixels, and with a vertical resolution 10 times the screen vertical resolution. Only the data waveforms themselves are printed. It does not print the axes or events, annotations etc. A horizontal scale bar of length equivalent to one grid section and vertical scale bars of lengths equivalent to each trace axis are also saved with the data.

Clipboard: Copying

A quick and easy way to export data for incorporation into other programs is by using the clipboard.

Bitmap

You can place a bitmap image of the display onto the clipboard with the Edit: Copy as bitmap command.

Metafile

You can copy a vector image to the clipboard using the Edit: Copy as metafile command (you can also write a metafile to disk with the File: Write metafile command). Vector images have the advantage that, unlike bitmaps, they can be scaled without loss of definition. However, the metafile image has the same resolution as the screen image, and so enlarging it does not produce a more detailed output.

To edit individual components in metafile images in an external program such as PowerPoint, you will have to ungroup them. In my experience, the way Office handles metafiles is a bit flaky.

Data values as text

You can also use the Edit: Copy traces as text command to copy the actual data values of traces visible on the screen to the clipboard in tab separated text format, so that you can paste them directly into a spreadsheet or graphing programme. The data values are read from file, so their full accuracy is maintained. However, you should be aware that this can require a lot of memory if you have data displayed with a high level of compression.

 


Previous           Next