In the "help depth" documentation is the following:
Gnuplot does not do true hidden surface removal for solid surfaces, but often
it is sufficient to render the component quadrangles in order from furthest
to closest. This mode may be selected using the options
set pm3d depthorder hidden3d
The `depthorder` option orders the solid quadrangles; the `hidden3d` option
similarly orders the bounding lines (if drawn). Note that the global option
`set hidden3d` does not affect pm3d surfaces.
However, the command above fails:
gnuplot> set pm3d depthorder hidden3d
constant expression required
So either there is a bug or the documentation needs to be fixed.
Anyway, looking at gnuplot after an absence makes me wonder about some syntax. For example, 'pm3d' isn't the most easy to understand. Even 'splot' is a bit arcane. Here is the documentation:
`splot` is the command for drawing 3D plots (well, actually projections on
a 2D surface, but you knew that). It can create a plot from functions or
data read from files in a manner very similar to the `plot` command.
One might wonder then, Why "splot" as opposed to, say, "plot3" or "plot3d"? What does the "s" mean? Of course, it means "surface plot". But have so many features been added that "surface plot" is no longer exactly accurate? If "splot" is preferred, could the word "surface" be worked into the documentation as a memory aid? Could the words "surface" and "mesh" be added to gnuplot syntax in a more meaningful way?