Frequency shown as a function of heliocentric distance. Radio triangulation results are plotted together with two density models (Saito, Leblanc) for comparison. The markers show the source positions of three different radio bursts and the bars attached to them show the distance between the wave vectors. Panel a: the black spheres show LF-type II, panel b: FI-type III is noted by the green squares, and panel c: the blue diamonds indicate the FD-type III.