Better axis scaling in scatter plot and related charts

[bburlacu]

Often chart axes need to be scaled according to the value range. This is done by setting reasonable min and max values and an interval between tickmarks. For example, the existing scaling in the scatter plot calculates the min and max of the data and then scales them by 20% (max *= 1.2, min *= 0.8), while the number of tickmarks is always set to 5. The downside of this method is excessive scaling (eg., when max is large, 0.2 becomes significant).

We suggest another approach for scaling, where the axis minimum, maximum and interval are calculated according to the position of the most significant fractional digit of the minimum value, and of the interval calculated as interval = range / ticks. This ensures that the tickmarks are always multiples of the interval and rounded to the most significant digit.

Examples:

• Old scaling

• New scaling:

[bburlacu]

r13764: Add ChartUtil methods and improved scaling in RegressionSolutionScatterPlotView r13765: Update project file.

[bburlacu]

r13807: Fix bug in Decimals methopd causing an infinite loop when the value is zero.

[gkronber]

The improvements to the scaling are a good idea. So, thanks for improving this!

However, I experienced a problem in the bubble chart after the changes in this ticket. Now, when I use the 'jitter'-feature in the bubble chart the scaling causes the points in the plot to jump around extremely. I think the automatic scaling for the bubble-chart with jitter should be therefore be handled specifically.

(See attachments, because of the new axis scaling the right hand side points are not visible after jittering)

[gkronber]

Another issue that has been introduced is handling of grid-lines in the bubble chart (after zooming in and then zooming out again, see attachment).

[bburlacu]

@gkronber: none of the changes under this ticket affected the bubble chart. the same issue occurrs in the download version of HeuristicLab, when changing the jitter value while the chart is zoomed in (this is also responsible for the grid lines artifact: zoom in, apply jitter, then zoom out). as far as I can tell the issue you reported has nothing to do with the axis scaling suggested here. will have a deeper look to find the real culprit for this issue.

[gkronber]

Replying to bburlacu:

@gkronber: none of the changes under this ticket affected the bubble chart.

OK, thanks

[bburlacu]

r14007: Fixed small scaling bug when calculating the necessary decimals for the axis interval.

[bburlacu]

r14008: Added chart util method to calculate the "optimal" axis interval (reducing the number of fractional digits to make it look nice). Modified the regression solution line chart and scatter plot to use the new scaling method.

[bburlacu]

r14014: Fixed small issue with layout update when the number of columns was changed. Improved layout of the configuration panel. Made GradientView invisible as an item in the Solution View.

[bburlacu]

r14152, r14155: Improved axis scaling.

[bburlacu]

r14156: Fix bug in scaling when interval is too small to be rounded to multiples of 5 or 10.

[bburlacu]

r14159: Slight improvement of scaling.

[mkommend]

r14161: Merged r13764, r13765, r13807, r14007, r14008, r14014, r14152, r14155, r14156, r14159 to stable.

[gkronber]

r14160: Fix very small omission.