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Re: fast scatter plots - advice sought


From: David Bateman
Subject: Re: fast scatter plots - advice sought
Date: Mon, 01 Feb 2010 20:30:15 +0100
User-agent: Mozilla-Thunderbird 2.0.0.22 (X11/20090706)

David Bateman wrote:
Jaroslav Hajek wrote:
On Fri, Jan 15, 2010 at 3:06 PM, dbateman <address@hidden> wrote:
Ok, so given this and the feedback from Shai both scatter and the gnuplot
backend do the wrong thing here. I'll fix this over the weekend.

Thanks
David


I didn't quite follow the information flow, but I noted that if in
Matlab you do scatter (x, y, s, c) where x, y, c are long column
vectors and s is a scalar, Matlab creates a single patch that can
handle the varying color, through property VertexCData or something
like that. Is this possible for Octave? If so, then in this case one
would not need to split by unique colors and sizes, but just by sizes,
which would probably be much faster when variable colors are used.

OTOH, when colors are specified as a full RGB Nx3 array, Matlab (2007)
seems to invariably make one patch per point.

Jaroslav,

It appears that gnuplot can handle a PM3D palette for lines in 2 and 3D, so can be quite easily handled in gnuplot itself. Something like the attached patch seems to work and the example

n=5000;x = randn(1,n); y = randn(1,n); c = sqrt(x.^2+y.^2); h = scatter(x,y,6,c)

is now quite fast with gnuplot. Do you see any issues with making a change like this?

D.

I pushed a different version as the treatment of scatter3 needs a bit of extra work for the cdata. However I couldn't get the fltk backend to plot the scatter plots correctly with or without the changeset I pushed

D.


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David Bateman                                address@hidden
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