[Gnuplot-bugs] unexpected difference between plot and splot of binary files with unstructured data

[cédric o. <ced...@gm...>]

Hello,

After having asked the question on the gnuplot list, I think it may be
a possible bug so I post my question to this list.

I have found a interesting comment on the web explaining how to plot
unstructured mesh written in a binary file in gnuplot. I knew to do
that in ascii but I have been looking for the binary possibility for a
while.

The command is for instance the following

plot 'file.dat' binary record=(15,-1) format='%float' u 1:2:3 w l palette

I wrote the binary file file.dat using octave (fwrite(file,vector)).

The 15 is because I plot cells of 5 points of two coordinates + the
value at the point (so 5x3).

cell=[ptA ptB ptC ptD ptA]
vector=[ptAx ptAy ptAval ptBx ptBy ptBval ptCx ptCy ptCval  ptDx ptDy
ptDval  ptAx ptAy ptAval ...];

The plot command gives the results I would expect with an ascii file.
However, the splot command does not because some cells of the
unstructured mesh are now connected although they should not.

In addition, this behaviour for splot is obtained with gnuplot 4.6 patchlevel 0.

Crossing lines are also observed for the splot AND plot commands on my
older version 4.2 patchlevel 2. Therefore, it is seems a correction
has been done between the two versions but only for the plot command.

Can someone tell mu if it is a bug or I misuse gnuplot?

Best regards,

Cédric