matplotlib-users Mailing List for matplotlib

I've been trying to figure out how to do this for a while.  I need to
make polar plots which go around clockwise and have 0deg on top (north)
instead of on the side (east).  How can this be done?

Jeff,

Thanks for the speedy reply. Should a warning be raised then that my  
data (though in 2D form) is not 2D and therefore is invalid input?

Cheers,

Josh Lawrence
Ph.D. Student
Clemson University

On Apr 16, 2009, at 2:53 PM, Jeff Whitaker wrote:

> Josh Lawrence wrote:
>> Greetings all,
>>
>> In using the function griddata in mlab.py, I think I have found a  
>> bug.  The following line in mlab.py errors for me.
>> I supply it an xi and yi that have shape (N,1). I have surface  
>> data,  but I only care about the variation in one direction. In  
>> mlab, when it  gets to this line (2956 in svn revision 7040):
>>
>>          if min(xo[1:]-xo[0:-1]) < 0 or min(yo[1:]-yo[0:-1]) < 0:
>>              raise ValueError, 'output grid defined by xi,yi must  
>> be  monotone increasing'
>>
>> the result is an error. That is, I get the following:
>>
>>          ValueError: min() arg is an empty sequence
>>
>> A couple of things. First, if I make my variation in x to be 2  
>> points  (x = 0 for the case I'm interested in--so I just have both  
>> values of x  be zero), I do not get this error and I believe the  
>> result works. So,  it seems that there should be some handling of  
>> the case that there are  only 1 point in either x or y direction.
>>
>> Second, is it better to use the builtin python function min, or  
>> should  numpy.min be used instead?
>>
>> Cheers,
>>
>> Josh Lawrence
>> Ph.D. Student
>> Clemson University
>
> Josh:  griddata currently only works for 2-D output grids.  It may  
> be possible to modify it to work with 1-D data, but that was not the  
> original intent of the function.
>
> -Jeff
>
> -- 
> Jeffrey S. Whitaker         Phone  : (303)497-6313
> Meteorologist               FAX    : (303)497-6449
> NOAA/OAR/PSD  R/PSD1        Email  : Jef...@no...
> 325 Broadway                Office : Skaggs Research Cntr 1D-113
> Boulder, CO, USA 80303-3328 Web    : http://tinyurl.com/5telg
>

> I am not sure what you are asking -- could you elaborate?

Sorry.  I use matplotlib to create PNGs graphics for display on a
web-page.  I want to make the plots zoom-able.  I'll use javascript to
capture the pixel positions of the user's selected zoom region on the
PNG plot.  I'll then translate this into the coordinate system on the
plot and redraw it with a new x, y range.  I'm having trouble
translating the initial axises into the pixel positions (essentially
where they are on the PNG image).

For example, I use the following code to map point positions from the
coordinate system to pixel positions.  I use an img map <MAP> to
provide interaction with the actual lines.

[CODE]

lineObj = plt.plot(Xs,Ys,marker='o')[0]
path, affine = lineObj._transformed_path.get_transformed_points_and_affine()
path = affine.transform_path(path)
for real,pixel in zip(lineObj.get_xydata(),path.vertices):
 ## write <AREA> tag  for each point

[/CODE]

I'd like to get information similar to this for the axis of the plot.

Thanks.

Josh Lawrence wrote:
> Greetings all,
>
> In using the function griddata in mlab.py, I think I have found a bug.  
> The following line in mlab.py errors for me.
> I supply it an xi and yi that have shape (N,1). I have surface data,  
> but I only care about the variation in one direction. In mlab, when it  
> gets to this line (2956 in svn revision 7040):
>
>           if min(xo[1:]-xo[0:-1]) < 0 or min(yo[1:]-yo[0:-1]) < 0:
>               raise ValueError, 'output grid defined by xi,yi must be  
> monotone increasing'
>
> the result is an error. That is, I get the following:
>
>           ValueError: min() arg is an empty sequence
>
> A couple of things. First, if I make my variation in x to be 2 points  
> (x = 0 for the case I'm interested in--so I just have both values of x  
> be zero), I do not get this error and I believe the result works. So,  
> it seems that there should be some handling of the case that there are  
> only 1 point in either x or y direction.
>
> Second, is it better to use the builtin python function min, or should  
> numpy.min be used instead?
>
> Cheers,
>
> Josh Lawrence
> Ph.D. Student
> Clemson University

Josh:  griddata currently only works for 2-D output grids.  It may be 
possible to modify it to work with 1-D data, but that was not the 
original intent of the function.

-Jeff

-- 
Jeffrey S. Whitaker         Phone  : (303)497-6313
Meteorologist               FAX    : (303)497-6449
NOAA/OAR/PSD  R/PSD1        Email  : Jef...@no...
325 Broadway                Office : Skaggs Research Cntr 1D-113
Boulder, CO, USA 80303-3328 Web    : http://tinyurl.com/5telg

On Thu, Apr 16, 2009 at 1:10 PM, Mark Larsen <lar...@gm...> wrote:

> MPL Users,
>
> How can I get the matched max and min pixel/coordinate positions of my
> x and y axises?



I am not sure what you are asking -- could you elaborate?

JDH

Greetings all,

In using the function griddata in mlab.py, I think I have found a bug.  
The following line in mlab.py errors for me.
I supply it an xi and yi that have shape (N,1). I have surface data,  
but I only care about the variation in one direction. In mlab, when it  
gets to this line (2956 in svn revision 7040):

          if min(xo[1:]-xo[0:-1]) < 0 or min(yo[1:]-yo[0:-1]) < 0:
              raise ValueError, 'output grid defined by xi,yi must be  
monotone increasing'

the result is an error. That is, I get the following:

          ValueError: min() arg is an empty sequence

A couple of things. First, if I make my variation in x to be 2 points  
(x = 0 for the case I'm interested in--so I just have both values of x  
be zero), I do not get this error and I believe the result works. So,  
it seems that there should be some handling of the case that there are  
only 1 point in either x or y direction.

Second, is it better to use the builtin python function min, or should  
numpy.min be used instead?

Cheers,

Josh Lawrence
Ph.D. Student
Clemson University

MPL Users,

How can I get the matched max and min pixel/coordinate positions of my
x and y axises?

Thanks,

LarsenMTL

Dear matplotlib users/developers,

I recently noticed that the errorbar funciton in the pyplot module  
changed it's default setting to fmt="-".
This is a bit strange since this function is primarily used to display  
individual data points with measurement errors, drawing a line  
connecting the datapoints is not a common procedure and normally only  
done with a fit to the data.
I think it makes much more sense if the default behaviour was fmt="+".

Kind regards,

Pim Schellart

Images, one is directly png and other converted from eps.

Andres

Andres Luhamaa wrote:
> Hello!
> Following example will give strange result in postscript output. It does 
> not happen, if I use imshow or contourf instead of pcolormesh and it 
> seems to happen only with log scale.
>
> Best regards,
> Andres
>
> import numpy as np
> import matplotlib
> matplotlib.use( 'PS' )
> from mpl_toolkits.basemap import Basemap
> import os
> import pylab as plt
> import matplotlib.colors as colors
> m=Basemap(width=1500000,height=1000000,resolution='c',projection='stere',lon_0=\
> 17,lat_0=58)
> # geogr coords for 
> points                                                      
> rx=np.arange(18,22,0.1)
> ry=np.arange(56,60,0.1)
> RX,RY=np.meshgrid(rx,ry)
> x,y=m(RX,RY)
> # create data for 
> points                                                       
> data=np.zeros([rx.size,ry.size])
> data[:10,:10]=1e3
> m.pcolormesh(x,y,data
>              ,norm=colors.LogNorm(vmin=50,vmax=17000.0)
>              )
> m.drawcoastlines()
> m.drawcountries()
> m.drawmapboundary()
> plt.colorbar()
> plt.savefig('mapproblem.eps')
>
>
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Hi, I want to put arrows onto the contours of a contour plot, the direction
will depend on whether the contour is positive/negative.  Before I try to do
it myself, has anybody written something to do that?

Thanks, Evan