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Quiverkey() positions arrow incorrectly with labelpos 'N' or 'S' #5613

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EdwinChan opened this issue Dec 3, 2015 · 5 comments · Fixed by #5620
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Quiverkey() positions arrow incorrectly with labelpos 'N' or 'S' #5613

EdwinChan opened this issue Dec 3, 2015 · 5 comments · Fixed by #5620
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@tacaswell
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v1.5.1

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@EdwinChan
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The documentation for quiverkey() in versions 1.3 through 1.5 states that

If labelpos is 'N' or 'S', X, Y give the position of the middle of the key arrow.

This guarantee is clearly violated in version 1.5:

quiver_1 4 3
quiver_1 5 0
quiver_1 5 0 548 g9230cac

The script that generated these figures is

import numpy
import matplotlib
from matplotlib import pyplot

plot = pyplot.quiver(*numpy.random.rand(2, 10, 10))
pyplot.xlim(-2, 12)
pyplot.ylim(-2, 12)
pyplot.quiverkey(plot, 0.5, 1, 1, 'N', labelpos='N')
pyplot.quiverkey(plot, 1, 0.5, 1, 'E', labelpos='E')
pyplot.quiverkey(plot, 0.5, 0, 1, 'S', labelpos='S')
pyplot.quiverkey(plot, 0, 0.5, 1, 'W', labelpos='W')
pyplot.annotate(matplotlib.__version__, (0, 0), (-1, 11), 'data', 'data',
  ha='left')
pyplot.savefig('quiver_{}.png'.format(matplotlib.__version__))
@mdboom mdboom added this to the Critical bugfix release (1.5.1) milestone Dec 3, 2015
@efiring efiring self-assigned this Dec 3, 2015
@efiring
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efiring commented Dec 3, 2015

I see what happened (in #3955), and it's easy to fix. I can do it today or tomorrow. Thanks for the report, @EdwinChan. Your script will inspire a test.

@tacaswell
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I do not see how I broke this 😞

@efiring
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efiring commented Dec 4, 2015

@tacaswell, You normalized to "middle", but quiverkey is still using "mid" and is not going through the normalization (and indeed, it shouldn't need to). So I will either change the normalization to "mid", or change quiverkey to request "middle".

@tacaswell
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Ah, I see. I can clean up my mess if you would like.

@efiring
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efiring commented Dec 5, 2015

OK, thanks.

tacaswell added a commit to tacaswell/matplotlib that referenced this issue Dec 5, 2015
@tacaswell
FIX: quiver key pivot location
34d601f 
In PR matplotlib#3955 / af17051 the quiver pivot
location was normalized to be 'tip', 'tail', or 'middle' internally.
The key 'mid' is now normalized to 'middle'.  The quiver key code
circumvents the normalization and was setting `Quiver.pivot' to 'mid',
which fell back to the default behavior of pivoting on the tail when the
quiver key is drawn.

closes matplotlib#5613
@tacaswell tacaswell mentioned this issue Dec 5, 2015
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@tacaswell tacaswell assigned tacaswell and unassigned efiring Dec 5, 2015
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FIX: quiver key pivot location tacaswell/matplotlib
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@mdboom @efiring @tacaswell @EdwinChan