[Gnuplot-info] SurfacePlotDataMatrixProducesAxesNoSurface

[Geoff K. <ge...@ka...>]

I am attempting to plot a surface from data in a file. The plot produced 
shows the correct X,Y, Z axes and key. But no surface and the base plane 
is not where I expect it to be.

For simplicity I am testing with the data inline using:
splot [X_min:X_max][Y_min:Y_max] '-' matrix
0.0046	-0.067	-0.1375	-0.2081	-0.2587	-0.3094	-0.3702	-0.4311	-0.495
0.097	0.026	-0.043	-0.1129	-0.1617	-0.2087	-0.2577	-0.3123 -0.3891
0.1774	0.0877	0.0226	-0.0425	-0.1011	-0.1598	-0.2069	-0.254	-0.3127
0.2578	0.1498	0.0882	0.0278	-0.0405	-0.1085	-0.1561	-0.1989	-0.2363
0.3034	0.2022	0.1448	0.0875	0.0233	-0.0408	-0.0947	-0.1486	-0.1892
0.3491	0.2587	0.2015	0.1438	0.0872	0.0285	-0.0333	-0.0951	-0.1421
0.4093	0.3214	0.256	0.1905	0.1377	0.085	0.0251	-0.0349	-0.0886
0.4695	0.3912	0.3104	0.2381	0.1883	0.1378	0.0834	0.0263	-0.0351
0.47660	0.4624	0.3798	0.2972	0.2372	0.1772	0.1293	0.0814	0.0225

The preamble and  splot call is contained in a gp script file like so:
[plot-xy-surface.gp]
#!/usr/bin/gnuplot -persist
reset session
set terminal wxt 1 persist enhanced

X_min=-18.5; X_max=-13.5; Y_min=-18.5; Y_max=-13.5;
Z_min=-0.6; Z_max=0.6

unset xtics;
set xrange [X_min:X_max]; set xtics X_min,0.5,X_max; set xlabel "X"
unset ytics;
set yrange [Y_min:Y_max]; set ytics Y_min,0.5,Y_max; set ylabel "Y"
set zrange [Z_min:Z_max]; set ztics Z_min,0.1,Z_max; set zlabel "Z"

unset key; set key outside

set xyplane 0.0
set grid; set cntrparam levels 13; set isosamples 100
splot ....

The terminal session is:
gnuplot> call "plot-xy-surface.gp"
gnuplot> show surface
	surface is drawn

I have tried many variations, and have now drawn a blank!  As mentioned 
above there is no surface, and the base plane is set at Z_min rather 
than 0.0 as requested!

Is there any option that I should be turning on or indeed off?

For reference:
GNUPLOT:	gnuplot 5.4 patchlevel 4
OS:		Debian 12  bookworm
DESKTOP		Mate 1.26.0

I have no problem using splot with functions.

Any input much appreciated.

-- 
Geoff