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I did some more digging and I think I have a hypothesis for what is
happening.
There is only one main difference between a call to .drawstates() and
.readshapefiles() with respect to loading and plotting data. .drawstates()
loads *only* the line segments that coincide with the defined map
boundaries, while .readshapefiles() loads all of the data in the shapefile.
Therefore, the LineCollection that gets attached to the axis contains data
from outside the stated domain.
In addition, the basemap versions of the plotting functions have the benefit
of finishing their calls with a call to .set_axes_limits(), which keeps the
axes in check. However, a non-basemap version would not call that
automatically, thereby having its axes automatically expanded to contain all
of the data in the LineCollection.
I am not sure what exactly should be done about this. This is certainly
un-intuitive behavior, though. Maybe there could be a keyword option in
.readshapefile() to have only the data for the stated domain loaded? That
might solve the issue.
Thanks,
Ben Root
On Fri, May 21, 2010 at 4:08 PM, Benjamin Root <ben...@ou...> wrote:
> Hello,
>
> I have been tracking down an annoying (but easily worked around) issue with
> Basemap. It seems that if you call .readshapefile() to create, for example,
> roads on your image, and then call any pyplot command afterwards for that
> axis, the axis will reset itself to the entire domain (I guess it would be
> the complete domain stated in the shapefile, maybe?). This does not happen
> if you call the equivalent function from the Basemap instance, though.
> Also, this does not happen with drawstates() and its ilk.
>
> I have made a test script and a couple of supporting shapefile in a tar.gz
> file to demonstrate the issue. It is available here:
> http://dl.dropbox.com/u/7325604/basemaptest.tar.gz
>
>
> I have also attached a png file showing the resulting image as it appears
> on my computer. I have no clue as to the cause and I hope that someone here
> might have an idea.
>
> Thanks,
> Ben Root
>

On 05/21/2010 03:55 AM, João Luís Silva wrote:
> Hi,
>
> Using the SVN version the following example fails with:
>
> File "/usr/local/lib/python2.6/dist-packages/matplotlib/colors.py", line
> 815, in inverse
> raise ValueError("Inversion requires valid vmax> vmin")
> ValueError: Inversion requires valid vmax> vmin
>
> This was introduced in svn revision 8308.
>
> Example script: ---------------------------------------
>
> import numpy as np
> import matplotlib.pyplot as plt
>
> plt.imshow(np.zeros((10,10)))
> plt.colorbar()
> plt.show()
>
> ------------------------------------------------
>
> Regards,
> João Silva
Thank you. It's fixed in 8331.
Eric
>
>
> ------------------------------------------------------------------------------
>
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> Matplotlib-devel mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel

If possible, can you try the latest svn version and see if it makes
any difference?
Also, see if increasing the dpi helps, i.e.,
savefig(..., dpi=150)
Given the nature of the rasterization, I'm not sure if we can
completely avoid the white gap for low dpi settings.
But the displacement issue you see (although think it has been fixed
in the svn) needs to be fixed.
Regards,
-JJ

Markus,
Looking again at your image, I realized that you are probably using real
data, not simulated data, therefore you can't easily use a higher grid
resolution.
So, I created a test script to examine this. I have found that there is
definitely a difference between filetypes. In my test script, there is a
white row that occurs for pcolor, but not for pcolormesh (Note, I have a
patched version of matplotlib that rasterizes pcolormesh). Also, this
effect does not happen if rasterization is set to False. Lastly, the effect
is more pronounced with lower-resolution data.
Let me clean up the test script so that the devels to use to visualize this
issue.
Ben Root
On Fri, May 21, 2010 at 9:45 AM, Markus Haider <mar...@ui...>wrote:
> Hi,
>
> Thank you for your reply.
>
> > I have been doing some testing with pcolor() and pcolormesh() with
> > regards to rasterization. I can not see a displacement when choosing
> > between different file types or with setting rasterized to be True or
> > False. What I have noticed is a half grid-space displacement between
> > pcolor() and pcolormesh().
>
> Can you see the displacement in the before enclosed pdf file?
>
> > You can see if this is the cause of your displacement by choosing a
> > higher resolution grid. In such a case, the displacement should be
> > smaller.
>
> How can I choose a higher resolution grid?
> Thank you for your help,
> Greetings,
> Markus
>
> > Ben Root
> >
> > On Fri, May 21, 2010 at 5:03 AM, Markus Haider
> > <mar...@ui...> wrote:
> > Hello,
> >
> > I make colormap plots in matplotlib using pcolor or
> > pcolormesh. With
> > both I have a problem:
> >
> > If I use pcolormesh ("p2 =
> > ax2.pcolormesh(10**temp,rasterized=True)") I
> > get perfectly small file sizes, but the position of the
> > rasterized
> > colormap is a little bit displaced with respect to the frame,
> > showing a
> > white border on the top and right side. Is this a bug, or can
> > I change
> > this?
> >
> > If I try with pcolor, I get the
> > message/usr/lib/pymodules/python2.6/matplotlib/artist.py:562:
> > UserWarning: Rasterization of
> > '<matplotlib.collections.PolyCollection
> > object at 0x2aac890>' will be ignored
> > warnings.warn("Rasterization of '%s' will be ignored" % self)
> >
> >
> > Thank you very much for your help,
> > Markus
> >
> >
> ------------------------------------------------------------------------------
> >
> >
> > _______________________________________________
> > Matplotlib-devel mailing list
> > Mat...@li...
> > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
> >
> >
>
>
>

Hi,
Thank you for your reply.
> I have been doing some testing with pcolor() and pcolormesh() with
> regards to rasterization. I can not see a displacement when choosing
> between different file types or with setting rasterized to be True or
> False. What I have noticed is a half grid-space displacement between
> pcolor() and pcolormesh().
Can you see the displacement in the before enclosed pdf file?
> You can see if this is the cause of your displacement by choosing a
> higher resolution grid. In such a case, the displacement should be
> smaller.
How can I choose a higher resolution grid?
Thank you for your help,
Greetings,
Markus
> Ben Root
> 
> On Fri, May 21, 2010 at 5:03 AM, Markus Haider
> <mar...@ui...> wrote:
> Hello,
> 
> I make colormap plots in matplotlib using pcolor or
> pcolormesh. With
> both I have a problem:
> 
> If I use pcolormesh ("p2 =
> ax2.pcolormesh(10**temp,rasterized=True)") I
> get perfectly small file sizes, but the position of the
> rasterized
> colormap is a little bit displaced with respect to the frame,
> showing a
> white border on the top and right side. Is this a bug, or can
> I change
> this?
> 
> If I try with pcolor, I get the
> message/usr/lib/pymodules/python2.6/matplotlib/artist.py:562:
> UserWarning: Rasterization of
> '<matplotlib.collections.PolyCollection
> object at 0x2aac890>' will be ignored
> warnings.warn("Rasterization of '%s' will be ignored" % self)
> 
> 
> Thank you very much for your help,
> Markus
> 
> ------------------------------------------------------------------------------
> 
> 
> _______________________________________________
> Matplotlib-devel mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
> 
> 

I have been doing some testing with pcolor() and pcolormesh() with regards
to rasterization. I can not see a displacement when choosing between
different file types or with setting rasterized to be True or False. What I
have noticed is a half grid-space displacement between pcolor() and
pcolormesh().
You can see if this is the cause of your displacement by choosing a higher
resolution grid. In such a case, the displacement should be smaller.
Ben Root
On Fri, May 21, 2010 at 5:03 AM, Markus Haider <mar...@ui...>wrote:
> Hello,
>
> I make colormap plots in matplotlib using pcolor or pcolormesh. With
> both I have a problem:
>
> If I use pcolormesh ("p2 = ax2.pcolormesh(10**temp,rasterized=True)") I
> get perfectly small file sizes, but the position of the rasterized
> colormap is a little bit displaced with respect to the frame, showing a
> white border on the top and right side. Is this a bug, or can I change
> this?
>
> If I try with pcolor, I get the
> message/usr/lib/pymodules/python2.6/matplotlib/artist.py:562:
> UserWarning: Rasterization of '<matplotlib.collections.PolyCollection
> object at 0x2aac890>' will be ignored
> warnings.warn("Rasterization of '%s' will be ignored" % self)
>
>
> Thank you very much for your help,
> Markus
>
>
> ------------------------------------------------------------------------------
>
>
> _______________________________________________
> Matplotlib-devel mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
>
>

Hi,
Using the SVN version the following example fails with:
File "/usr/local/lib/python2.6/dist-packages/matplotlib/colors.py", line 
815, in inverse
 raise ValueError("Inversion requires valid vmax > vmin")
ValueError: Inversion requires valid vmax > vmin
This was introduced in svn revision 8308.
Example script: ---------------------------------------
import numpy as np
import matplotlib.pyplot as plt
plt.imshow(np.zeros((10,10)))
plt.colorbar()
plt.show()
------------------------------------------------
Regards,
João Silva

Hello,
I make colormap plots in matplotlib using pcolor or pcolormesh. With
both I have a problem:
If I use pcolormesh ("p2 = ax2.pcolormesh(10**temp,rasterized=True)") I
get perfectly small file sizes, but the position of the rasterized
colormap is a little bit displaced with respect to the frame, showing a
white border on the top and right side. Is this a bug, or can I change
this?
If I try with pcolor, I get the
message/usr/lib/pymodules/python2.6/matplotlib/artist.py:562:
UserWarning: Rasterization of '<matplotlib.collections.PolyCollection
object at 0x2aac890>' will be ignored
 warnings.warn("Rasterization of '%s' will be ignored" % self)
Thank you very much for your help,
Markus