hydro.pro is a preserved example of contouring and surface plotting for irregularly spaced 3-D data.

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TRIANGULATE, cx, cy, tr, b
tdata3d = FLTARR(100, 100, 6)
!P.MULTI = [0,3,2]

FOR level = 0,5 DO BEGIN
   tdata = trigrid(cx, cy, data6(*,level), tr, [1,1], [1,1,100,100])
   CONTOUR, tdata, levels=[1,10,100,1000], C_LABELS=[1,1,1,1]
ENDFOR