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Re: [Matplotlib-users] Fwd: Strange behaviour on plotting data on Ronbinson projection using Basemap
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From: Chao Y. <cha...@gm...> - 2014-04-16 11:54:43
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Dear Phil, Thank you. This solves my problem. So the title of my mail is wrong, the behaviour is reasonable but I am using wrong coordinates. And also thanks to Jeff. Cheers, Chao On Wed, Apr 16, 2014 at 10:14 AM, Phil Elson <pel...@gm...> wrote: > Hi Chao, > > The warning you are getting: > > WARNING: x coordinate not monotonically increasing - contour plot > may not be what you expect. If it looks odd, your can either > adjust the map projection region to be consistent with your data, or > (if your data is on a global lat/lon grid) use the shiftgrid > function to adjust the data to be consistent with the map projection > region (see examples/contour_demo.py). > > Is important here. It looks like the x coordinate is not in appropriate > longitudes. Printing the first 5 and last 5 longitudes gives us our first > clue: > > First 5: [-180. -178.99720764 -177.99443054 -176.99163818 -175.98886108] > Last 5 : [ 175.98886108 176.9916687 177.9944458 178.9972229 180.00003052] > > Notice that the last longitude wraps around beyond 180. So if we were to > clip these numbers to -180 and +180 we will see that the warning disappears > and the contour is correct. This can be achieved with: > > lon = np.clip(lon, -180, 180) > > Alternatively, we can just construct the latitudes and longitudes > ourselves directly with: > > lon, lat = np.meshgrid(np.linspace(-180, 180, 360), np.linspace(-90, 90, > 180)) > > Incidentally, I tried these numbers with cartopy which has been designed > to handle dateline wrapping automatically, and the contour worked with the > unmodified longitudes (http://nbviewer.ipython.org/gist/pelson/10830039). > > --------------------------- > > @JeffWhitaker - This looks like a bug with float tolerances in the > makegrid function. It currently does: > > def makegrid(self,nx,ny,returnxy=False): > dx = (self.urcrnrx-self.llcrnrx)/(nx-1) > dy = (self.urcrnry-self.llcrnry)/(ny-1) > > But might be better if it did: > > def makegrid(self,nx,ny,returnxy=False): > x = np.linspace(self.llcrnrx, self.urcrnrx, nx) > y = np.linspace(self.llcrnry, self.urcrnry, ny) > > To avoid the multiplicative floating point drift that is currently being > seen. > > HTH, > > Phil > -- please visit: http://www.globalcarbonatlas.org/ *********************************************************************************** Chao YUE Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL) UMR 1572 CEA-CNRS-UVSQ Batiment 712 - Pe 119 91191 GIF Sur YVETTE Cedex Tel: (33) 01 69 08 29 02; Fax:01.69.08.77.16 ************************************************************************************ |
