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How does Sampling Work?

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Randy Minder
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Randy Minder asked on 19 Jan 2012, 10:05 PM
I've read the documentation on sampling but it's still not clear to me exactly what RadChart is doing. For example I have a Scatter chart with approximately 3000 data points. The data points are spread, fairly evenly, across approximately 6 hours of time along the X axis. In other words, data is not disproportionately bunched anywhere along the X axis. It's pretty evenly spread out. The Y axis values range from approximately 60 to 66, with no particular pattern. Can you tell me exactly how RadChart would sample this data, assuming I select a sampling value of say 300 (1/10 of the data). I have not specified the method of sampling (average, min, max etc.), because I don't really know which would be best in my case.

Thank you.

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Yavor
Telerik team
answered on 20 Jan 2012, 09:27 AM
Hello,

The sampling mechanism is used to approximate the resulting data, and show only a part of it. More information on it is available here:

http://www.telerik.com/help/silverlight/radchart-features-sampling.html

Two special points deserve attention.
First, the mechanism used. The charting engine simply runs a calculation on all the data, and renders an average, based on the sampling threshold. As mentioned in the help topic, this does not take into account the positions where the points will be rendered. Thus, if the original data contains cluttered subsets with many points, the sampe may include them too.
The second point is the mode used in the sampling. This determines the value of the sample. For example, if you have 10 points, and choose "Min" as the SamplingFunction, the point with the smallest value will be used.
Another alternative to sampling is zooming and scrolling.

I hope this information helps.

Greetings,
Yavor
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