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emcc
15 Posts |
 Posted - 12 Aug 2009 : 19:31:05
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I have noticed a problem when drawing scatterplots using a high zoom - results in an Overflow Error in UpdateDraw. (using C#, VS2005, QCChart2DNet.dll v1.7.1.4)
To reproduce the error, in the SimpleLineAndScatterPlots.cs example, set the y-axis scale:
pTransform1.SetScaleY(50.0, 50.00001);
If you comment out the 2 scatterplots in the example, the error doesn't occur.
What is the limit for small scales like this? |
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quinncurtis
1164 Posts |
Posted - 13 Aug 2009 : 09:41:19
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We use some .Net 2D transformation routines in the .Net Matrix class for handling the scaling, translation and rotation of the scatter plot symbols. The Matrix class only uses floats (4-byte reals) in its calculations. The data has range of 10^2, and the display range 10^-6, so there is a 10^8 resolution required in the calculations. The result is producing roundoff errors in the Matrix float calculations that ultimately lead to the overflow error you see. So, you must limit your zooming to a dynamic range less 8 orders of magnitude. We see no work around with the software in its current form (and Rev. 2.0 also). It would require a rewrite of the ScatterPlot symbol plotting routines to eliminate the use of the Matrix class to make it work under the conditions you describe. If it is critical to your application, we could probably do that under contract at a nominal cost.
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Zoom limitation for scatterplots
