Re: [Matplotlib-users] Question on LineCollection

[Justin M. <jn...@gm...>]

On Wed, Jul 13, 2011 at 6:49 PM, Benjamin Root <ben...@ou...> wrote:
> On Wednesday, July 13, 2011, Justin McCann <jn...@gm...> wrote:
>> $ ipython -pylab
>> # ====
>> from matplotlib.collections import LineCollection
>> f = figure()
>> plot()
>> ax = gca()
>> vec = numpy.random.random((10,3))
>> segs = []
>> for i in range(0, len(vec)):
>>     x1 = vec[i][0]
>>     #x1 = 3000000
>>     x2 = vec[i][1]
>>     #x2 = 4000000
>>     y1 = y2 = vec[i][2]
>>     segs.extend( [[(x1,y1),(x2,y2)]] )
>>
>> line_segments = LineCollection(segs, linewidth=3, alpha=0.3, colors =
>> 'r', linestyle = 'solid')
>> ax.add_collection(line_segments)
>> ax.set_xlim(0,1)
>> ax.set_ylim(0,1)
>> show() # hmmmm... nothing yet
>> draw() # force a draw; now it works
>>
...
> Just an observation (I haven't tested anything)... But what is up with
> the call to plot()?  It might be causing issues with the autoscaler.
> Any line collections created without other plotting functions is going
> to need the axes limits set.
>
> Ben Root
>

Yeah, that was weird. :)

I added that when I was first messing around, and the axes didn't show
up even when I called show(). If you do the draw() at the end, then
you don't need to call plot(), and then you also don't need to mess
with the view limits (set_{x,y}lim).

I guess the moral of the story is, "if you don't explicitly plot() [or
a variant], you must explicitly draw()."

===
from matplotlib.collections import LineCollection
f = figure()
ax = gca()
vec = numpy.random.random((10,3))
segs = []
for i in range(0, len(vec)):
   x1 = vec[i][0]
   x2 = vec[i][1]
   y1 = y2 = vec[i][2]
   segs.extend( [[(x1,y1),(x2,y2)]] )

line_segments = LineCollection(segs, linewidth=3, alpha=0.3,
colors='r', linestyle='solid')
ax.add_collection(line_segments)
draw() # force a draw; now it works
====