Re: fast scatter plots - advice sought

[Jaroslav Hajek]

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