Plotting

3D Views

Polar and Cartesian 3D data views are available through a distinct window launched from the Plot menu on the QSAS main window as a separate 3D View menu item.

The 3D View window has three tabs, Data, Plot Options and Page and plots into its own plot window which is independent of the main plot window.

The Data tab has a data drop slot which expects a 3 dimensional array or array sequence. When a time series object is dropped in, the record/time slider is active and the record to be plotted can be selected with the slider or typed into its record field. If the Auto-replot button is selected, then changing the record will automatically replot the data at the new record. The plot will automatically choose the first two dimensions with units of degrees or radians as the angular dimension in polar plots, but this can be over-ridden using the R dimension selector on the options tab.




The Plot Options tab allows the user to control the plot design, but defaults for all options are set according to the data and its metadata. The plot and axis titles can be explicitly set in the appropriate fields. The Plot Type can be Data Points (coloured symbols at the physical location) and/or Ribbons (blocks of colour along one dimension at fixed values in another dimension and variable ribbon width in the third dimension) or Slice. The symbol used for data points can be set, along with its base size. The size also scales with depth along the line of sight, so that foreground points are larger than those behind to aid perspective. Ribbon type plots provide surfaces along one dimension; they have variable width and are constant in another dimension. Slices, on the other hand may be taken across any axis or a user specified normal, and sliders on the plot allow the slice to be interactively moved through the data.
The vector from the distribution centre to the slice centre (marked X on the plot) may be saved to the working list from the plot window. Thus the location of a feature in the data may be identified by adjusting the sliders until the X is on the feature. Note that this can be a bit of a fiddle at first, and is easiest achieved by using the viewing angles to estimate the position of the feature in theta and phi, then with these angles set adjust the radial slice position. Small adjustments of all sliders will then allow positioning the X at the centre of where the feature appears largest. Note the slice uses no interpolation, so the bin boundaries will appear in the slices. However, the slice uses 100 bins in both radius and angle, spaced linearly, so features will normally be resolved down to the data bin level, and if logarithmic radius is selected the slice bins are also logarithmic.

The Axis Type field allows either Polar or Cartesian coordinates to be used, and when Auto detect is chosen (default) the axes will be polar if an angle variable is found as one of the dimensions. The Opacity of the points or ribbons can be set with Opacity. Changing opacity can be viewed as changing the opacity at the bottom of the colour bar with a linear variation up to the top which is always opaque. Thus when Opacity is set to 1.0 all colours are opaque, and when it is set to 0.0 the top of the colour bar is opaque but opacity varies linearly to the bottom of the colour bar being transparent. Opacity may be negative, in which case the fully transparent colour is above the bottom of the colour bar.

The Radial dimension (and all cartesian dimensions) can be plotted in the log, in which case zero or negative values are automatically excluded. If the radial quantity is anywhere negative then, when log radius is selected, the minimum value in r is subtracted from each radial value and this offset noted in the text pane. In addition the first non-zero radial value is used as lower limit, but this may be over-ridden by manually setting the radial minimum value. Negative radial values are permitted for linear radial plots.

Similarly the data dimension (colourscale) may be logarithmic, in which case the lowest non-zero value is used when autoscaling. The colour scale range may be manually over-ridden.
The font sizes and line width for axes can be controlled.

The Page tab controls the paper size, resolution when printed (where appropriate) and paper orientation. Custom paper sizes can be specified, and all measurements are in the units set in the Units field. Page controls are the same as for the 2D polar plots.

The viewing angle for the plot can be controlled by the sliders on the 3D plot pane, and the viewing angle is shown on its title bar.

The 3D plot pane itself holds an Animate View button which will continually change the viewing angle for 30 seconds, starting from the current viewing angle, and an Animate Time button which will successively plot each data record in the input data object from the current time slider position to the end. Animate Time will first calculate a suitable colourscale for the whole time interval if the Auto Colourscale toggle is on, and this will cause a delay before animation starts with large data sets.

Under normal use each plot will appear in the same window created the first time Plot is pressed. The New window for each plot toggle allows a fresh window to be created each time Plot is pressed, and selecting the Plot window id of an existing window allows it to be overwritten (after deselecting New window for each plot).

Printing or saving a plot to a file is achieved using the Plot menu from the 3D plot pane itself after plotting.

The Sample session shipped with QSAS contains a saveset (saveSet.qx_3dview_plot) for a 3D ribbon plot of the ion data in the sample session with the opacity set to -0.4 to emphasise the location of the data peak. The resulting plot should look as follows:

Last up-dated: October 2016 Tony Allen