Re: bug in depthorder?

[Daniel J S. <dan...@ie...>]

Petr Mikulik wrote:
> The enclosed script using the "pm3d depthorder" gives wrong ordering of 
> faces on gnuplot-cvs, and sometimes wrong and sometimes good ordering on 
> gnuplot 4.2. Also try to rotate the plot by mouse. How can this happen?

Petr,

depthorder is a very much an approximation to true hidden surface features.  I think there was some discussion a couple years ago about this.  If I'm remembering correctly, I wrote a patch for determining the depth which I thought was a bit more robust.  But after discussions with Ethan, I thought it would be more worthwhile putting effort into actual hidden surface, if one had time.  (A generalization of the hidden lines code where a hidden surface is broken into smaller parts.)

The problem in your example is that the surfaces are too big relative to the resolution such that in 3D space their depths overlap.  Furthermore, this example is probably undersampling anyway because the peaks aren't visible.

Try

set dgrid3d 100,100
replot

and you should get improvement in the behavior of both.  (But there are still hidden surface flaws.)

Dan


> 
> ***
> 
> f(x,y)=sin(x*y*pi/180)/(x*y*pi/180)
> 
> if (1)  set xrange [-720:720]; set yrange [-720:720]; \
>         set sample 10; set isosamples 10; set table 'a.dat'; splot f(x,y); 
> unset table; reset
> 
> set auto fix
> #set xrange [0:10]; set yrange [0:10]
> set xlabel "x axis"; set ylabel "y axis"
> set xyplane at 0
> 
> set pm3d
> 
> set pm3d depthorder
> 
> set view 64, 287
> splot 'a.dat' with pm3d
> 
> pause 1
> 
> set view 64, 286; replot
> 
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-- 

Dan Sebald
email: daniel(DOT)sebald(AT)ieee(DOT)org
URL: http://www(DOT)dansebald(DOT)com