JFreeChart adding trendline outside of actual values?

Question

I generate a chart using three data series (using XYSplineRenderer in JFreeChart) and for some reason the blue and red curves have an almost polynomial fit in some spots. The program seems to think there is an imaginary data point above and below the curve.

Any ideas? Thanks!

Answer 1

An XYSplineRenderer "connects data points with natural cubic splines," so the effect is expected. You might look at adjusting the precision, as shown here.