Add y-scale logarithmic axis to Windrose chart

[tkreyche]

The Windrose chart has an inherent flaw that is not specific to your implementation of it. But it can (probably) be resolved if you allow a y-axis log scale option. I've tried log scale on the y-axis and it throws an error. I don't see the option documented for the Windrose chart.

The problem is pretty simple: a high wind event is not (or barely) visible on the Windrose chart under the following conditions:

1. it is of relatively short duration
2. the direction of the event is not consistent with the otherwise prevailing wind

In this case the chart "pie slice" will be extremely short and this event show up so small on the chart that it's invisible.
It may be that the chart is more designed to show typical events, but it having a y-axis log scale would add flexibility.

One option is to show two Windrose charts side by side, with one restricting the y-axis maximum to 5% or so and not restricting the other chart's y-axis but is not ideal since it takes more real estate and may be confusing to some people.

thanks, Tom Kreyche

[tkreyche]

Here's a prototype app example.
The top Windrose chart has max y-axis is restricted to 5%. The bottom chart has no restriction.

There is a wind event event of 10 to 15 kt (and direction of SE). It shows as 1%. See blue arrows for the event. For the rest of the time period, the wind velocity is under 10kt.

It is visible on the top restricted polar chart, but invisible on the bottom chart.
Maybe log scale is not ideal, but there are other azimuthal projections options such as orthographic that might work.

[TorsteinHonsi]

Thanks for writing!

First of all, polar charts support logarithmic y axis out of the box. The error you experienced was probably error 10, because the axis min is set to 0. A log axis cannot go to 0, so by setting it slightly higher, it works: https://jsfiddle.net/highcharts/rjoephd7/.

That said, there's something wrong with how the latest series overlap the whole stack. The > 10 category (yellow) seems to render on top of the other elements. That should be treated as a bug.

[TorsteinHonsi]

Workaround

Until the fix is released - the columns that extend to the end are 0-value columns. By replacing 0 by a very small value it should render okay.