English: Colour image of isosurfaces of a bipolar coordinate system with foci at (-1,0) and (1,0). Red contours are plotted for values in the interval [-2,2] in steps of 0.2 while the red contours are plotted from in the range (-π/2,π/2) in steps of π/20.

The first version is a vector graphic version (SVG) of existing file Iso1.png which is a contour plot for bipolar coordinates.

It uses only many many straight strokes to "draw" the curves. Produced using Inkscape, LaTeX and wxmaxima.