1. Why don't you write a decent documentation ?

       Because I don't like this tedious job.
       Besides, thousands (OK hundreds now) of users have
       used xd3d without a doc. It is built to be easy to use.

2. Can xd3d do cross-sections ?

       YES !
       Since version 8.2.0

3. What is this weird error message "Points confondus" ?????

      (since version 8.2.0 it has been translated into "*** merged points")
      .xyz files are supposed to represent a surface in 3d passing
      through all the given points. A 2d Delaunay mesh is first generated 
      using the (x,y) coordinates. It implies two important things:

    1/ The (x,y) coordinates must be distinct up to a tolerance
       parameter which depends on the domain size. If two (x,y) points 
       are equal according to this tolerance, you get an error message:
       *** merged points: 3 6
       meaning that the point number 3 and 6 are equal in the (x,y)
       plane, even if their z coordinates are different.

    2/ The Delaunay mesh support is the convex enveloppe of the cloud
       of (x,y) points. Don't expect to draw a star with an .xyz file.

4. Why Fortran ???
       
       Why not ?
       If it is a so big problem for you, you can convert the
       sources through "f2c" or rewrite the whole thing in 
       C++/Java/Ocaml :)

5. Any OpenGL version ?

       Not yet. The genesis of xd3d is very old, a time when
       OpenGL was not even dreamed. It has been written in a
       portable way with only basic graphical instructions.
       But I agree that an OpenGL version could be nice.