[SciPy-dev] Contouring algorithm in xplt

Travis Oliphant oliphant at ee.byu.edu
Fri Mar 7 16:09:40 CST 2003

Hi all,

I know the subject of contouring has come up a time or two.  It has been
mentioned that GIST has a good contouring algorithm.  While I can't speak
to the quality of a contouring algorithm at this point, I can let you know
that the contour algorithm is exposed to Python in xplt.

It is xplt.contour

With this routine you can take a 2-D array, define a level and it will
spit out points (xc,yc) which define the contour.   It appears to be very
fast as well.

Chaco is coming along.   I would like to help it grow though it is
difficult to come up to speed with all the fancy threading and object
class proxying that is going on.  Plus, I still get occasional segfaults
which I can't track the source of.

One concern I have is whether or not it will ever be fast.  Right now,
the update that occurs when scrolling a sliding bar in the wxplot demo is
annoyingly slow (long flashes everytime the sliding bar is touched).

Right now, I'm comfortable with xplt and can do any number of graphs and
it is very flexible and VERY FAST.

Plotting is such a hang-up right now for the adoption of SciPy that I
wonder if it wouldn't be wise to port xplt to Windows (I actually don't
think it would take that long and I could hire a student to do over the
next few months).

It's not the ideal long-term solution but it would give us a known, fast
plotting interface (kind of like Matlab 4.2 plotting) for simple plots and
we could then continue to develop chaco as the long-term solution without losing
valuable potential contributors who can't find the plotting package, or
get it to work.

Perhaps all of this is already available with gnuplot and we just need to
do a better job of interfacing with it, but I'm not sure.

Anyway, I guess I'm venting a little frustration that it is very difficult
for me to get chaco working stably and well to do anything more than a few
gimmick plots rather slowly, when xplt has worked reliably for me for
several years and is working quite well to do all sorts of visualization,
yet nobody seems to want to use it but me.

I'll get back to hacking now.


Travis Oliphant
Assistant Professor
459 CB
Electrical and Computer Engineering
Brigham Young University
Provo, UT 84602
Tel: (801) 422-3108
oliphant.travis at ieee.org

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