Re: fast scatter plots - advice sought

[Robert T. Short]

Kai Habel wrote:
> -------- Original-Nachricht --------
>    
> > Datum: Mon, 11 Jan 2010 08:22:03 +0100
> > Von: Jaroslav Hajek<address@hidden>
> > An: David Bateman<address@hidden>
> > CC: octave maintainers list<address@hidden>
> > Betreff: Re: fast scatter plots - advice sought
> >      
>    
> > On Mon, Jan 11, 2010 at 8:17 AM, David Bateman<address@hidden>
> > wrote:
> >      
> > > Jaroslav Hajek wrote:
> > >        
> > > > hi,
> > > >
> > > > I recently started some work where I'm going to use scatter plots
> > > > heavily with a few thousand points.
> > > > I found out, however, that scatter plots were unusably slow with so
> > > > many points. This has also been reported before:
> > > >
> > > > http://old.nabble.com/scatter3-is-really-slow-to24312164.htm
> > > >
> > > > by this changeset
> > > > http://hg.savannah.gnu.org/hgweb/octave/rev/2f435ed48143
> > > >
> > > > I tried to optimize the plotting strategy to get more reasonable
> > > > times, especially in the simplest cases. The old strategy of creating
> > > > one object per point is only used for small numbers of points (<= 20).
> > > > Otherwise, the points are split into subsets with common color and
> > > > size, and these subsets are plotted using a single primitive. This
> > > > seems similar to what Matlab does.
> > > >
> > > >          
> > > If this is done in the baackend ok, but I deliberately didn't make this
> > > change in the frontend as it breaks matlab compatibility
> > >
> > >        
> > What breaks Matlab compatibility? Please explain. Note that it is
> > *not* true that Matlab always creates one object per point (as you
> > seemed to imply in the above linked mail), at least in 2007a. It does
> > so only when there is a small number of points:
> >
> >      
> > > > n = 10;
> > > > h = scatter (rand (n, 1), rand (n, 1))
> > > >          
> > h =
> >
> >    159.0022
> >
> >      
> > > > get(h,'children')
> > > >          
> > ans =
> >
> >    169.0011
> >    168.0011
> >    167.0011
> >    166.0011
> >    165.0011
> >    164.0011
> >    163.0011
> >    162.0011
> >    161.0015
> >    160.0012
> >
> >      
> > > > n = 1000;
> > > > h = scatter (rand (n, 1), rand (n, 1))
> > > >          
> > h =
> >
> >    159.0028
> >
> >      
> > > > get(h,'children')
> > > >          
> > ans =
> >
> >    160.0013
> >
> > I bet the strategy Matlab uses is similar to ours. I didn't
> > investigate the switch point, but I don't really think compatibility
> > is needed at that level.
> >
> > regards
> >
> > --
> > RNDr. Jaroslav Hajek, PhD
> > computing expert&  GNU Octave developer
> > Aeronautical Research and Test Institute (VZLU)
> > Prague, Czech Republic
> > url: www.highegg.matfyz.cz
> >      
>
>
>
> I did a quick check with 2009a:
>
>    
> > > n=100;h=scatter(rand(n,1),rand(n,1),'vi','off');ch=get(h,'ch');length(ch),get(ch(1),'Type')
> > >        
> ans =
>
>     100
>
>
> ans =
>
> patch
>
>    
> > > n=101;h=scatter(rand(n,1),rand(n,1),'vi','off');ch=get(h,'ch');length(ch),get(ch(1),'Type')
> > >        
> ans =
>
>       1
>
>
> ans =
>
> patch
>
> So, the switching point is at 100/101. For 101 points and beyond matlab uses a 
> single patch object to draw all data points.
>
> Kai
>
>
>    
The way things are done now, scatter is useless for more than a very 
small number of points and I think MATLAB compatibility should be 
dropped if uselessness is the result of compatibility.  However, it 
sounds like we are NOT currently compatible with MATLAB and becoming 
compatible might fix the problem.

Bob
--
Robert T. Short, Ph.D.
PhaseLocked Systems