gnuplot-live

This is an entirely javascript-based implementation of gnuplot v.4.6.3 based on the work here: gnuplot-JS. I updated it some to use CodeMirror for the editor and setup the output image to allow resizing.
The output file must be 'out.svg' (and use svg terminal). You can "upload" (not uploaded, just stored in browser memory) data files with the button below.

Optional: Grant the program read-access to a specific file on your local computer. This file is _not_ uploaded anywhere. Use it for data files that you want to use in your script.

set terminal svg enhanced size 1000,700
set output 'out.svg'
# set terminal svg size 600,400 dynamic enhanced fname 'arial'  fsize 10 mousing name "heatmaps_3" butt solid 
# set output 'heatmaps.3.svg'
set format cb "%4.1f"
set view 49, 28, 1, 1.48
set samples 70, 70
set isosamples 60, 60
set ticslevel 0
set cbtics border in scale 0,0 mirror norotate  offset character 0, 0, 0 autojustify
set title "4D data (3D Heat Map)\nIndependent value color-mapped onto 3D surface" 
set title  offset character 0, 1, 0 font "" norotate
set xlabel "x" 
set xlabel  offset character 3, 0, 0 font "" textcolor lt -1 norotate
set xrange [ 5.00000 : 35.0000 ] noreverse nowriteback
set ylabel "y" 
set ylabel  offset character -5, 0, 0 font "" textcolor lt -1 rotate by -270
set yrange [ 5.00000 : 35.0000 ] noreverse nowriteback
set zlabel "z" 
set zlabel  offset character 2, 0, 0 font "" textcolor lt -1 norotate
set pm3d implicit at s
set colorbox user
set colorbox vertical origin screen 0.9, 0.2, 0 size screen 0.03, 0.6, 0 front noborder
Z(x,y) = 100. * (sinc(x,y) + 1.5)
sinc(x,y) = sin(sqrt((x-20.)**2+(y-20.)**2))/sqrt((x-20.)**2+(y-20.)**2)
color(x,y) = 10. * (1.1 + sin((x-20.)/5.)*cos((y-20.)/10.))
GPFUN_Z = "Z(x,y) = 100. * (sinc(x,y) + 1.5)"
GPFUN_sinc = "sinc(x,y) = sin(sqrt((x-20.)**2+(y-20.)**2))/sqrt((x-20.)**2+(y-20.)**2)"
GPFUN_color = "color(x,y) = 10. * (1.1 + sin((x-20.)/5.)*cos((y-20.)/10.))"
splot '++' using 1:2:(Z($1,$2)):(color($1,$2)) with pm3d title "4 data columns x/y/z/color"

gnuplot-live

Output: