Heatmap issue

Hello,

I am evaluating your solution for HeatMap Chart (I think it is rely amazing). I need to display a HeatMap Series with 1024 points.

I modified your demo project (http://www.mindscapehq.com/blog/index.php/2013/11/14/new-wpf-heatmap-chart/) :

1. I set x axis Maximum to be 1000 [Chart.XAxis.Maximum = DateTime.Now.Date.AddMinutes(1000);]
2. I updated number of points to 1000. (In CreateSeries method : w = 1000)

And I got some strange result:

If you zoom in chart or change number of points to be 800, the problem disappears.

How can I resolve this issue?

Problem 2:

1. I defined heat map series and each point has value 0, 1 or 1000;

2. I defined LinearGradientBrush in the following way:

      <LinearGradientBrush>
       <GradientStop Offset="0" Color="Transparent" />
       <GradientStop Offset="1" Color="Blue" />
       <GradientStop Offset="1000" Color="Red" />
     </LinearGradientBrush>
   

Purpose: Points with value = 0 will be Transparent, points with the value = 1 will be Blue, points will value 1000 will be Red

The problem - all the points with value = 1 are not displayed. (Possibly they are transparent)

When I changed the offset of red color to 100, the problem was resolved ( all the points with value = 1 were Blue)

I will be glad if you can help me with the issue.

I attached the sample project for the second problem.

Thanks, Pavel

Hello Pavel,

Apologies for the late reply, we've been away on break. Great to hear that you really like out heatmap series.

For your first issue, this is a bug on our end. The heatmap series has data sampling enabled by default which means that when too much data is being displayed in the view-port, it skips every second data point. All series have this and just work due to how they're implemented. Heatmap series however needed a bit more work for the data sampling to look correct - change the resolution of the rendered data points to fill in the skipped columns of data.

I have made this fix at our end which you can get in the next nightly build. The next nightly build will be available after 1200 GMT and can be downloaded from here: http://www.mindscapehq.com/products/wpfelements/nightly-builds

As for the second issue, this is caused by an optimization that I used in the heatmap implementation. Rather than interpolating the gradient for ever single data cell (and for every single frame if your chart is dynamic), I split the gradient into 300 evenly spaced colors along the gradient. Then for each data cell being rendered, I round it to the closest point along the gradient and can instantly get the color for it. This dramatically improves the performance. Currently this is not configurable, but I can add this in for you if you find that you need it - note that allowing for a wider range of colors will affect the performance though.

This means that your data values of 1 are being "rounded" down and so falling into the transparent color bucket. Any improvements to this at our end are going to affect the performance, so first, please try one of the following solutions. These solutions are based on my assumption that the reason you are creating this gradient is so that the legend bar is skewed and so doesn't show the transparent item.

1. Change the value of red to be 300. This will cause 0, 1 and any value above 300 to fall into the colors that you expect them to be. This does cause a few pixels of transparency to appear in the legend gradient bar however.

2. Use the built in missing-datapoint feature. If your application is going to use double values as the data points (like in the demo you posted), then you can set the value in the arrays to Double.NaN that you don't want to be displayed. Then, set the MissingColor property of the HeatmapSeries to be transparent. The series will then always render NaN values as transparent. Then you can remove the transparent point from the gradient.

3. If you can not use Double.NaN, and you want to make sure transparent doesn't show up in the legend bar, then follow the first suggestion, but also create your own implementation of the HeatmapGradientConverter which ignores transparent values. Let me know if you need help with this suggestion.

Hope that helps! let me know if you have any questions about anything I've mentioned here.

-Jason Fauchelle

Hello Jason,

Thank you for the quick response and for giving me solutions for the issues.

For the first issue, I'll download the next nightly build. For the second issue I will use your first solution and I will normalize values to be within range [0, 300].

Thanks, Pavel