Colum items not rendered properly when using a logarithmic Y axis

[G30rges]

As discussed there: http://discussion.oxyplot.org/topic/1041311-colum-items-not-rendered-properly-when-using-a-logarithmic-y-axis/#

In the oxyplot sample, there are two demos making use of Bars and Columns: BarSeriesDemo and ColumnSeriesDemo.
For the first, using a logarithmic axis in place of the linear one as Y axis does not cause any problem, the values are displayed correctly:

However, when doing the same with the demo ColumnSeriesDemo, the bars are not drawn correctly it seems, looks like they are "reversed":
In the class ColumnSeriesDemo.MainWindow, I changed the lines 43 and 44 from
tmp.Axes.Add(new CategoryAxis { ItemsSource = this.Items, LabelField = "Label" });
tmp.Axes.Add(new LinearAxis { Position = AxisPosition.Left, MinimumPadding = 0, AbsoluteMinimum = 0 });
To

tmp.Axes.Add(new CategoryAxis { Position = AxisPosition.Bottom, ItemsSource = this.Items, LabelField = "Label" });
tmp.Axes.Add(new LogarithmicAxis { Position = AxisPosition.Left, Minimum = 1, Base = 10 });

With code behind:

With xaml, without the log Y axis:

Why doesn't it behave the same way?

[G30rges]

For my bars to display "properly", I have to set a base Value = 1 on the series. The problem is I might have values < 1, then they don't get displayed. I need to have a minimum = 0 on the Y axis declaration and the same for the categories values.

[G30rges]

Does your commit fix the bug?

Cheers

[objorke]

No, it was just adding your example reproducing the bug.

[Codebeisser]

The same issue occurs with stem plot.
See: https://stackoverflow.com/questions/47887366/oxyplot-logarithmic-stem-plot-is-upside-down

[udaykolluru]

@objorke i tried with different graphs with logarithmic axis for area, line, scatter, i can also see the same issue ,is there any fix ,or quick fix for this .

Can you please suggest the fix for the above problem

[VisualMelon]

@udaykolluru which issue exactly? Line, scatter, and 2-line area series should be fine, since they don't need a base-line. It sounds like you may have a different problem: could you provide some example code?

---

The behaviour described above is certainly inconsistent (which isn't ideal), but logarithmic scales don't have a natural finite zero. Area plots (of which histograms and column plots are different types) usually don't make sense with a logarithmic y-axis, because the area always has to be relative to some baseline.

I'd expect the default behaviour to be that the bar goes on to -infinity (which the data probably is, and is probably causes issues with different renderers: e.g. WPF 'inverting' large and small values is a common symptom), but that's basically of no use to anyone: you need to pick a meaningful baseline; if you don't have a meaningful baseline, then you should probably reconsider using a chart with an area.

Some more commentary on column charts with logarithmic scale can be found in the graph pad guide

[swethakini-ofc]

@VisualMelon @objorke I was trying LogarithmicAxis with HistogramSeries in latest Oxyplot 2.0. The graph looks inverted. How can this be corrected?
Logarithmic Axis

Linear Axis

[VisualMelon]

@swethakini-ofc HistogramSeries always uses a base value of zero, so it can't be fixed: what is happening is that log(0) is negative infinity. I don't think it makes any sense to use a histogram on a non-linear axis, because the area and height are both meaningful quantities, but if you can explain a use case where a non-zero base would make sense, maybe we could extend it.

[swethakini-ofc]

@VisualMelon What about Column Series. Even excel provides logarithmic scale for Y axis

Excel

[VisualMelon]

@swethakini-ofc with column series, you can set the BaseValue to 1 in order to achieve that.

[swethakini-ofc]

@VisualMelon Thanks this worked 👍