matplotlib uses some C-based contouring code that began life in GIST. You can see it here:
http://matplotlib.svn.sourceforge.net/viewvc/matplotlib/trunk/matplotlib/src/cntr.c?revision=5781&view=markup It has some limitations, notably around certain donut-shaped contours, and a number of us have made attempts to improve it or replace it with something else suitably licensed, but that's the best we've been able to do for now. Mike Lionel Roubeyrie wrote: > Hi all, > just a little question : how matplotlib computes contours? Is it based > on an internal library? Is it possible to access it from outside? > Thanks > > Le vendredi 30 janvier 2009 à 10:22 -0500, Eli Brosh a écrit : > >> Hello again, >> I finally found the command I was looking for. It is the >> to_polygons(). >> Here is what worked : >> >> # make a LineCollection of contours >> col=contour(X,Y,Z,LevelsNumber).collections >> >> >> for i in np.arange(0,LevelsNumber,1): >> polygoni=col[i].get_paths()[0].to_polygons()[0] >> print polygoni >> >> All the vertices in each collections are extracted to the "polygoni". >> >> Thanks again to Jeff and Patrick ! >> >> By the way, I found out that I do not actually need this procedure to >> achieve may goal >> which was to make a contour plot in ternary coordinates. >> >> Eli >> >> >> >> On Tue, Jan 27, 2009 at 11:08 PM, Patrick Marsh >> <patrickmars...@gmail.com> wrote: >> On Tue, Jan 27, 2009 at 7:16 PM, Eli Brosh <ebro...@gmail.com> >> wrote: >> > Many thanks to Jeff and to Patric ! >> > I will try to work along the line suggested by Jeff. >> > Patric, please send me your code. >> > I hope to learn from it. >> > >> > Thanks again, >> > Eli >> >> >> >> Here is a template that can be used. I use this for >> meteorological >> models, but should work with any gridded file. >> >> >> import numpy as np >> from mpl_toolkits.basemap import Basemap >> >> f = (some gridded file) >> X = np.array(grab longitudes from f) >> Y = np.array(grab latitudes from f) >> field = np.array(grab field to be contoured from f) >> map = Basemap(make a Basemap call here) >> level = np.arange(minval, maxval, interval) >> col = map.contour(X, Y, field, level).collections >> >> for vertex in col[i].get_paths(): # GET THE PATHS FOR THE >> EACH >> CONTOUR BY LOOPING THROUGH CONTOURS >> for vertex in xy.vertices: # ITERATE OVER THE PATH >> OBJECTS >> x, y = map(vertex[0],vertex[1],inverse=True) # >> vertex[0] >> and now 'x' is the longitude of the vertex and vertex[1] and >> now 'y' >> is the latitude of the vertex >> >> >> Let me know how this works. >> >> -Patrick >> >> >> >> >> >> >> >> >> >> >> > >> > On Tue, Jan 27, 2009 at 7:09 PM, Patrick Marsh >> <patrickmars...@gmail.com> >> > wrote: >> >> >> >> On Tue, Jan 27, 2009 at 5:33 PM, Jeff Whitaker >> <jsw...@fastmail.fm> wrote: >> >> > Eli Brosh wrote: >> >> >> Hello, >> >> >> I am trying to extract the coordinates of contour lines. >> >> >> I tried the following: >> >> >> >> >> >> cs = *contour*(Z) >> >> >> for lev, col in zip(cs.levels, cs.collections): >> >> >> s = col._segments >> >> >> >> >> >> that I found in a previous post (title "contouring", by >> Jose >> >> >> Gómez-Dans-2 >> <http://www.nabble.com/user/UserProfile.jtp?user=30071> >> >> >> Nov 30, 2007; 07:47am ) . >> >> >> >> >> >> I hoped that s will be a list of numpy arrays, each >> containing the >> >> >> (x,y) vertices >> >> >> defining a contour line at level lev. >> >> >> However, I got an error message: >> >> >> AttributeError: 'LineCollection' object has no attribute >> '_segments' >> >> >> >> >> >> >> >> >> How is it possible to get coordinates of the contours, >> similar to the >> >> >> MATLAB command >> >> >> [C,H] = *CONTOUR*(...) >> >> >> where the result in C is the coordinates of the >> contours. >> >> >> >> >> >> A similar question appeared in a post "contour data" (by >> Albert Swart >> >> >> <http://www.nabble.com/user/UserProfile.jtp?user=382945> >> May 17, 2006; >> >> >> 09:42am) but I could not understand the answer. >> >> >> Is it possible to get more specific directions with a >> simple example ? >> >> >> >> >> >> >> >> >> Thanks >> >> >> Eli >> >> > Eli: Calling get_paths() on each line collection in >> CS.collections will >> >> > return a list of Path objects. From the Path objects, >> you can get a Nx2 >> >> > array of vertices from the "vertices" attribute. There >> are no examples >> >> > that I know of, but if you get it to do what you want to >> do, it would be >> >> > great if you could contribute an example. As you noted, >> this question >> >> > has come up several times before. >> >> > >> >> > -Jeff >> >> > >> >> > -- >> >> > Jeffrey S. Whitaker Phone : (303)497-6313 >> >> > Meteorologist FAX : (303)497-6449 >> >> > NOAA/OAR/PSD R/PSD1 Email : >> jeffrey.s.whita...@noaa.gov >> >> > 325 Broadway Office : Skaggs Research Cntr >> 1D-113 >> >> > Boulder, CO, USA 80303-3328 Web : >> http://tinyurl.com/5telg >> >> > >> >> > >> >> > >> >> > >> >> > >> >> ------------------------------------------------------------------------------ >> >> > This SF.net email is sponsored by: >> >> > SourcForge Community >> >> > SourceForge wants to tell your story. >> >> > http://p.sf.net/sfu/sf-spreadtheword >> >> > _______________________________________________ >> >> > Matplotlib-users mailing list >> >> > Matplotlib-users@lists.sourceforge.net >> >> > >> https://lists.sourceforge.net/lists/listinfo/matplotlib-users >> >> > >> >> >> >> I'm not sure if this is entirely what you (Eli) are looking >> for, but I >> >> have code that will contour model data on a map and then >> extract the >> >> lat,lon pairs of all the vertices. If this is what you are >> looking >> >> for, I'm happy to share what I've done. >> >> >> >> -Patrick >> >> >> >> -- >> >> Patrick Marsh >> >> Graduate Research Assistant >> >> School of Meteorology >> >> University of Oklahoma >> >> http://www.patricktmarsh.com >> > >> > >> >> >> >> >> -- >> >> Patrick Marsh >> Graduate Research Assistant >> School of Meteorology >> University of Oklahoma >> http://www.patricktmarsh.com >> >> >> ------------------------------------------------------------------------------ >> This SF.net email is sponsored by: >> SourcForge Community >> SourceForge wants to tell your story. >> http://p.sf.net/sfu/sf-spreadtheword >> _______________________________________________ Matplotlib-users mailing >> list Matplotlib-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/matplotlib-users >> -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ------------------------------------------------------------------------------ This SF.net email is sponsored by: SourcForge Community SourceForge wants to tell your story. http://p.sf.net/sfu/sf-spreadtheword _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
