I'm using achartengine to display real-time data. Does anyone know if it's possible to take an integral of the graph displayed by using some nice methods of achartengine? Or do I have to resort to my approximations with rectangles? Thanks in advance!
No there is no way to achartengine to calculate the integral. To get a number value for the integral you would need to either do a approximation you self or if you have a well defined function use some sort of mathematical library.
Depending on what sort of data you have there are several ways to do the approximation, if you got a equidistant dataset with a reasonable resolution just summing them up will give you a simple approximation.