Plotting contours together with 'with image' data

[Dima K. <gn...@di...>]

Hi. I have a matrix data set, and I'd like to plot it using colors (with
image), AND I'd like to overlay contours on top. This apparently does
not work.

It looks like 3d 'with image' plots use the data values for colors, but
NOT for z. I.e. you get a colored image at z=0. Since it looks like
contours read the z coordinate to do their thing, this doesn't work.

If I plot 'with lines', I get contours. I can also plot 'with pm3d',
which produces a color AND a z-coordinate, so contours work then.

Questions:

It makes no sense to me that 'with image' 3d plots are stuck at z=0.
Does ANYBODY want that? Can we apply the values to color AND z in this
case? Is this hard, or is there some specific reason we're doing it the
way we're doing it?

pm3d is intended for irregularly-sampled data (as I understand it), so
is there overhead for using pm3d in this case? Size? Speed? If there's
no overhead, can 'splot with image' simply map to 'splot with pm3d'?

If nothing else, can we barf instead of silently not rendering the
contours in the 'with image' case?

I'm attaching a sample data file.

Thanks!