WPF Graph log scale grid lines too dense

[The_Bn]

Hi, I'm using logarithmic vertical scale and minor grid lines, and that's what I have when the range is too wide:

How can I avoid grid lines being so dense that they touch each other?

I would like to preserve behavior that new "minor divisions scale" starts each major division, like here on the pic, and also I'm OK with major divisions being automatically chosen depending on how I resize the control. The most acceptable way for me would be setting number of minor divisions between neighboring major divisions, but I didn't find so far how I can set this.

[phansen · Accepted solution]

The way to change the subdivisions is by setting the Mode of the MinorDivisions on the axis. Unfortunately, the “Count” mode will always divide the range evenly across the screen, and will not reflect the logarithmic change in spacing. To achieve that, you can use a custom mode:

public class FixedCountSubdivisionsMode : RangeDivisionsMode {
    public int Count { get; set; } = 10;

    protected override IList<TData> GetDivisionsCore<TData>( IRangeDataMapper<TData> dataMapper, int divisionsEstimate ) {
        return Auto.GetDivisions( dataMapper, divisionsEstimate );
    }

    protected override IList<TData> GetSubdivisionsCore<TData>( IRangeDataMapper<TData> dataMapper, IList<TData> dependentDivisions ) {
        // (Note: this example assumes a "double" axis type)
        var majorDivisions = (IList<double>)dependentDivisions;
        var pairs = majorDivisions.Zip( majorDivisions.Skip( 1 ), Tuple.Create );
        var subdivisions = pairs.SelectMany( pair =>
            Enumerable.Repeat( (pair.Item1 + pair.Item2) / Count, Count - 1 )
                      .Select( ( interval, i ) => pair.Item1 + interval * i )
        );
        return subdivisions.Cast<TData>( ).ToList( );
    }
}

You can set this on your axis in XAML:

<ni:AxisDouble.MinorDivisions>
    <ni:RangeDivisions>
        <ni:RangeDivisions.Mode>
            <local:FixedCountSubdivisionsMode Count="5" />
        </ni:RangeDivisions.Mode>
    </ni:RangeDivisions>
</ni:AxisDouble.MinorDivisions>

Or in code:

axis.MinorDivisions = new RangeDivisions { Mode = new FixedCountSubdivisionsMode { Count = 5 } };

The CustomLogarithmicRangeDivisionsMode created for another question works similarly, but will always show subdivisions approaching every intervening logarithm power across the range, instead of just the major divisions.

[The_Bn]

Thanks! This works fine after few changes:

var subdivisions = pairs.SelectMany(pair =>
    Enumerable.Repeat((pair.Item2 - pair.Item1) / Count, Count - 1)
              .Select((interval, i) => pair.Item1 + interval * (i + 1))
);

[phansen]

(Sorry, was definitely paying more attention to the divisions setup, than the actual math — thanks for fixing my averaging and off-by-one errors ∶)