# StackedSplineAreaSeriesDefinition point to point curve

1. ##### NS
189 posts
Member since:
Jan 2007

Posted 26 Jan 2010 Link to this post

Hi,

This chart consists of 4 series. 3 times a StackedSplineAreaSeariesDefinition and one time a LineSeriesDefinition.

During user acceptance testing of this particular project, the end-users wondered why (in the case of the StackedSplineAreaSeriesDefinition) there is no straight line between two points with the same value. (in the screenshot between 3 and 3, between 2,5 and 2,6 and between 16 and 16). The Area curves a bit between those two points however the start and end value are the same ...

Thanks,
Nicolas
2. ##### NS
189 posts
Member since:
Jan 2007

Posted 26 Jan 2010 Link to this post

Please find attached another screenshot to illustrate this problem. (the blue stackedsplinearea)
The numbers "6" in the example marked by an arrow show a deflection in their point to point color. The other "6"s to the right don't have this problem.

3. ##### Ves
2926 posts

Posted 28 Jan 2010 Link to this post

Hello Nicolas,

This is actually the expected behavior. When calculating the curve between two points, their outer neighbors' values are taken into account. Let us take a set of 4 points P0, P1, P2 and P3. The curve between P1 and P2 is influenced by P0 and P3 in the following manner. The straight line defined by P0 and P1 would be the tangent at P1 and the straight line between P2 and P3 would be the tangent at P2.

This is better shown in your second image -- for the second pair of [6, 6] you have marked, the values of 11 and 6 influence the curve between the inner points - both at 6.. As the right outer point is again 6, the curve tends to go horizontal at the second "6" point.

You can find more details in this blog post by Charles Petzold and in his demo.

Best regards,
Ves
the Telerik team

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