It seems that there is a bug in plcont when using f90 binding
Using the same parameters for coordinate transformations compare to plimagefr gives a wrong contour.
See example 16:
I also have a test case attached. data to use it are here:
http://pascal.parois.net/public/data (quite big, sorry)
I need to transform xtrans(i,j) this way to fix it:
xtrans(i,j)= mod(xtrans(i,j)+ytrans(i,j), 2*planerealhalfwidth)
PS: the use of mod causes glitches in the contour, it's not a bug of plplot