Currently, Moodle uses a fairly old and limited graphlib (Graph Class. Version: 1.6.3 * Copyright (C) 2000 Herman Veluwenkamp).
In my current efforts at introducing the new "Personality Test" feature into the Questionnaire plugin, I wanted to output some results as a radar chart, and others as a "bi-polar" chart. I came across the pChart library, which does exactly what I want. See examples below.
pChart is already used in some Moodle (3rd-party) plugins. It is also used by the current version of LimeSurvey (v. 2). On the LimeSurvey site there is an interesing Comparison of different charting libraries, although it dates back to 2009.
I was wondering if there are any plans to update the graph/chart library included in Moodle to something more current and powerful.
Here are 2 examples of output done with pChart and the Questionnaire module (WIP new features).