Countour Plotting use DB data

I recently got a requirement to plot a contour map using data from a database. The amount of data can vary greatly [in the sense that you might get data for a 16x16 matrix or even a 1600x1600 matrix].
The data was originally used to plot a heat-map and contains cartesian coods and signal strength [quantifier value].
I am currently using C/C++ with openGL base for the current scenario and cannot link python or matlab [adding python would require its files to be added as pre-requisite, while matlab requires licensing].

I was hence hoping if someone could possibly link me to some github / bitbucket code to get an idea from. Alternatively if openGL has its own libraries for supporting this [I am quite new to this library].