在matplotlib底图图像上设置注释会导致无法撤消的宽度/高度错误

Question

I'm having a problem with plotting annotations on basemap and saving the image to a file. I have seen this problem raised several times before, but in my case following the advice didn't work and then the error persists even when reversing the code back to a previously working version without annotations.

Basically, without annotations, the figure has been plotting without problem for weeks. Now if I add around 130 annotations to the graph I get:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
C:\Users\Joshua\Canopy\scripts\Client Model\nicoleheatmap3.py in <module>()
    251     '''       
    252     #plt.show()
--> 253     plt.savefig('Demand_map.png',bbox_inches="tight",figsize=(800/96, 800/96),dpi=1600)
    254     plt.close()
    255 

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\pyplot.pyc in savefig(*args, **kwargs)
    575 def savefig(*args, **kwargs):
    576     fig = gcf()
--> 577     res = fig.savefig(*args, **kwargs)
    578     draw()   # need this if 'transparent=True' to reset colors
    579     return res

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\figure.pyc in savefig(self, *args, **kwargs)
   1474             self.set_frameon(frameon)
   1475 
-> 1476         self.canvas.print_figure(*args, **kwargs)
   1477 
   1478         if frameon:

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\backends\backend_qt5agg.pyc in print_figure(self, *args, **kwargs)
    159 
    160     def print_figure(self, *args, **kwargs):
--> 161         FigureCanvasAgg.print_figure(self, *args, **kwargs)
    162         self.draw()
    163 

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\backend_bases.pyc in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, **kwargs)
   2209                 orientation=orientation,
   2210                 bbox_inches_restore=_bbox_inches_restore,
-> 2211                 **kwargs)
   2212         finally:
   2213             if bbox_inches and restore_bbox:

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\backends\backend_agg.pyc in print_png(self, filename_or_obj, *args, **kwargs)
    519 
    520     def print_png(self, filename_or_obj, *args, **kwargs):
--> 521         FigureCanvasAgg.draw(self)
    522         renderer = self.get_renderer()
    523         original_dpi = renderer.dpi

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\backends\backend_agg.pyc in draw(self)
    462         if __debug__: verbose.report('FigureCanvasAgg.draw', 'debug-annoying')
    463 
--> 464         self.renderer = self.get_renderer(cleared=True)
    465         # acquire a lock on the shared font cache
    466         RendererAgg.lock.acquire()

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\backends\backend_agg.pyc in get_renderer(self, cleared)
    479 
    480         if need_new_renderer:
--> 481             self.renderer = RendererAgg(w, h, self.figure.dpi)
    482             self._lastKey = key
    483         elif cleared:

C:\Users\Joshua\AppData\Local\Enthought\Canopy\User\lib\site-packages\matplotlib\backends\backend_agg.pyc in __init__(self, width, height, dpi)
     92         self.height = height
     93         if __debug__: verbose.report('RendererAgg.__init__ width=%s, height=%s'%(width, height), 'debug-annoying')
---> 94         self._renderer = _RendererAgg(int(width), int(height), dpi, debug=False)
     95         self._filter_renderers = []
     96 

ValueError: width and height must each be below 32768

So my first thought was that I have a problem with the way I'm adding annotations iteratively (I had other errors earlier trying to feed it an array), so hashed that code out ie back to my old code base, and the problem is still there. I restart the kernel in Enthought Canopy and it's happy again, then adding annotations breaks it again until a kernel restart.

This is the code:

    m = Basemap(projection='merc',llcrnrlon=53.898184,llcrnrlat=24.019957,urcrnrlon=56.721985,urcrnrlat=26.076649,lon_0=55.545,lat_0=24.735,resolution='i')
    base_image = plt.imread("UAEpeninsulagrey.jpg")
    implot = plt.imshow(base_image)
    m.imshow(base_image,origin='upper')

    a,b = m(preparePlot[1],preparePlot[0])
    m.scatter(a,b,marker="o",s=preparePlot[2],color="#0000FF",alpha=0.5,)

    c,d = m(preparePlot[4],preparePlot[3])
    m.scatter(c,d,marker="o",s=6,color="#FF0000",alpha=0.5,)

    '''   
    for t in range(len(annotations[0])):
        x,y = m(annotations[1][t],annotations[0][t])
        x2,y2 = m(annotations[4][t],annotations[3][t])
        plt.annotate(annotations[2][t],xy=(x,y),xytext=(x2,y2),arrowprops=dict(facecolor='black', shrink=0.05),fontsize=2) 

    '''       

    #plt.show()  
    plt.savefig('Demand_map.png',bbox_inches="tight",figsize=(800/96, 800/96),dpi=1600)
    plt.close()

Some other strange things. I believe I'm explicit and correct in limiting the width and height already in plt.savefig (taken from previous SO threads eg this ) that this shouldn't be happening? Also, plt.show() does not throw an error. I require the high resolution to be able to zoom in to the map at street level. I have been able to get single annotations onto the image with no problem, even annotations for locations outside of the map area, which I thought could have been causing it to try display something way outside of the image.

Setting DPI down to 200 does not remove the error. Renaming annotations array didn't make any difference (in case it somehow caused problems for basemap internals).

Does anyone have any suggestions on how to stop this? Have I incorrectly set something up in plt.savefig ? Many thanks in advance.

PS The annotations array:

annotations[0][0]
Out[14]: 26.053275624999998

annotations[1][0]
Out[15]: 56.068128225

annotations[2][0]
Out[16]: 'Tot: 1, 0%'

annotations[3][0]
Out[17]: 26.043275624999996

annotations[4][0]
Out[18]: 56.058128225000004

Answer 1

After so many hours, I tracked it down to a conflict with bbox_inches="tight" Removing this will remove the error when a label is slightly angled to come outside the frame of the original picture (which happens because of my lat/long offset for label position). I'm not sure that the error message provides any meaningful feedback to the root cause of the problem :(