Trouble getting colormap set_under and set_over to work with PolyCollection

I’m trying to control the over and under colors of a color bar with set_under

and set_over on a ListedColormap object. I do not see the colors change, but I

do see the arrows added to the color bar.

For example, the following code mostly works but the calls to set_under and

set_over seem to have no effect. I’m trying to use the color bar documentation

at as a guide. Maybe I’m

doing something wrong or the example is slightly off?

I’m using matplotlib 1.4.0.

You can see examples of the images I’m generating here:

It’s been suggested to on the above tracker to use imshow. However, that

doesn’t address the issue I’m having using PolyCollection. In addition, I’m

not sure how to translate my example below so that it will work with imshow

because I’m trying to plot a 2D slice of a 3D array.

The code in question is below. Sorry for not including re-usable array data in

the example. My specific case is with a large 3D array that has several

thousands vertices, etc. Again, you can see the image examples here:

import numpy

import matplotlib as mpl

import matplotlib.pyplot as plt

from matplotlib.collections import PolyCollection

vertices = numpy.load(‘vertices.npy’)

array = numpy.load(‘array.npy’)

Take 2d slice out of 3D array

slice_ = array[:, :, 0:1].flatten(order=‘F’)

fig, ax = plt.subplots()

poly = PolyCollection(vertices, array=slice_, edgecolors=‘black’, linewidth=.25)

cm = mpl.colors.ListedColormap([(1.0, 0.0, 0.0), (.2, .5, .2)])




bounds = [.1, .4, .6]

norm = mpl.colors.BoundaryNorm(bounds, cm.N)

bounds = [0.0] + bounds + [1.0]

fig.colorbar(poly, ax=ax, orientation=‘vertical’, boundaries=bounds, norm=norm, extend=‘both’)

ax.add_collection(poly, autolim=True)




I don't think this has anything to do with PolyCollection versus Image, and I was not suggesting that you use imshow. What I am suggesting is that you take my example and make the minimal changes required to convert it back to using your PolyCollection; or go the other way. I think the key point is the call to the colorbar method.



On 2015/02/17 12:24 PM, Luke Lee wrote:

It's been suggested to on the above tracker to use imshow. However, that
doesn't address the issue I'm having using PolyCollection.