Re: [matplotlib-devel] Contour and Vector Plots

[John H. <jdh...@ac...>]

>>>>> "Helge" == Helge Avlesen <av...@ii...> writes:

    Helge> http://www.ii.uib.no/~avle/mpl/c1.png

    Helge> the first points of the segments are given by the vectors
    Helge> (x1,y1) the second (x2,y2). you can get pretty lines in
    Helge> matplotlib as well, but only by using the scattered line
    Helge> drawing methods of gtk. (something like
    Helge> self.area.window.draw_segments(self.gc, zip( x1,y1,x2,y2)?)

OK, I see.  I didn't fully understand that x1,x2,y1,y2 were the verts
of unordered line segments.  Then one can easily use a LineCollection
to draw these efficiently in matplotlib - script below and screenshot
http://nitace.bsd.uchicago.edu:8080/files/share/kontour.png.  Jeez, I
feel bad for sitting on this since February!

    Helge> if you want do do it "right" in matplotlib, you should
    Helge> implement a contour following algorithm (in C) - with this
    Helge> I mean an routine that returns the linesegments defining
    Helge> each countour in bundles. the current alg. is sort of
    Helge> marching cubes in 2D, a simplified version of CONREC
    Helge> http://astronomy.swin.edu.au/~pbourke/projection/conrec/
    Helge> but only using 2 triangles per square.

Do you have any thoughts on how we might do labels with your code?

    Helge> doing contour following alg. it is also much easier to
    Helge> implement automatic contour labelling. I suspect python
    Helge> loops are too slow for such algorithms - it may perhaps be
    Helge> possible to do them in Numeric, but it will still be much
    Helge> slower than my simple library. I think you may use the
    Helge> GPL'ed PLPLOT (C) for an example of contour following alg.

We have a problem in that we cannot use GPL'd code in matplotlib
because the GPL does not allow redistribution of closed code, which
the matplotlib (and python license) do.

If we decide to go with your routines, at least for the time being
until we can "do it right", would you be willing to contribute your
code to matplotlib under the matplotlib license (PSF inspired, free
for commercial and noncommercial reuse)?

Thanks!
JDH

from matplotlib.matlab import *
from matplotlib.collections import LineCollection
import hutil

delta = 0.05
x = y = arange(-3.0, 3.0, delta)
X, Y = meshgrid(x, y)
Z1 = bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
Z2 = bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
Z = Z2-Z1

print Z.shape
fsm = ones(Z.shape, Z.typecode())


zmax, zmin = hutil.maxmin(Z)
depths=linspace(zmin, zmax, 10)

x1,y1,x2,y2 = hutil.contour2(Z, fsm, depths )

imshow(Z, origin='lower', interpolation='nearest')

segments = [ ( (thisy1, thisx1), (thisy2, thisx2) ) 
             for thisx1, thisy1, thisx2, thisy2 in zip( x1,y1,x2,y2)]

coll = LineCollection(segments)
gca().add_collection(coll)
savefig('kontour')

show()