pcolor and "interp"

[Ben Abbott]

  was Subject: Re: [changeset] clarification to pcolor doc-string

I've not yet attempted to change __go_draw_axes__.m, but I have been  
able to determine what needs to be changed in the gnuplot stream for  
the interpolation to work.

One qualifier; the result is not equivalent to Matlab, which uses a  
bilinear interpolation, enabled by segmenting each rectangular cell  
into a pair of triangles.

In any event, using gnuplot 4 lines of the stream need to be  
modified.  I'll use the short example supplied by jwe to demonstrate.

	pcolor (peaks ());
	shading interp
	drawnow ("x11", "/dev/null", false, "debug.gp")

The 4 lines in debug.gp which require modification are listed below.

< 42 set pm3d explicit at s  corners2color c3;
 > 42 set pm3d explicit at s interpolate 2, 2 corners2color c3;
< 43 set pm3d explicit at s depthorder corners2color c3;
 > 43 #set pm3d explicit at s depthorder corners2color c3;
   44 set pm3d explicit;
   45 unset hidden3d;
   46 set xrange [-3.000000000000000e+00:3.000000000000000e+00]  
noreverse;
   47 set yrange [-3.000000000000000e+00:3.000000000000000e+00]  
noreverse;
< 48 set zrange [-1.000000000000000e+00:1.000000000000000e+00]  
noreverse;
 > 48 #set zrange [-1.000000000000000e+00:1.000000000000000e+00]  
noreverse;
[...]
< 62 splot "-" using ($1):($2):($3):($4) title "" with pm3d linestyle  
1 \
 > 62 splot "-" using ($1):($2):($4) title "" with pm3d linestyle 1 \

After making the changes, the result may be rendered by

	gnuplot -persist debug.gp

The part, "interpolate 2, 2", increases the <steps in scan> and <steps  
between scans>, respectively. In this instance I've increase each from  
1 to 2. The general format for this is;

	set pm3d interpolate <steps in scan>,<steps between scans>

I am not yet prepared to explain way the changes are needed for the  
zrange or why ($3) needed to be removed. but I need to make each of  
these changes to produce a proper result. I'm running gnuplot 4.2.3.

If some one is running a version of gnuplot more recent than v4.2.3,  
I'd be interested is how it handles the result.

I'll look into __go_draw_axes__.m tomorrow, but if anyone has some  
functional understanding of the details ... please jump in.

Ben