Re: [Matplotlib-users] Apparent bug in Data limits with LineCollections

[Eric F. <ef...@ha...>]

Chris,

Christopher Barker wrote:
> Hi all,
> 
> I'm having problems with the data limits when I use a LineCollection
> 
> Here is the relevant code. A VectorLinecollection is a subclass of 
> LineCollection. ax is an Axes instance.
> 
>         ax.clear()
>         VLC  = VectorLineCollection(t, y, theta, self.Figure, ax)
>         ax.add_collection(VLC)
>         ax.plot(t, y, 'o')
>         print "The lines are:", ax.get_lines()
>         print "AutoScaleOn:", ax._autoscaleon
>         print  ax.dataLim.intervaly()
>         print ax.dataLim.intervaly().get_bounds()
>         ax.autoscale_view()
> 
> 
> This all works fine when I call it the first time, but when I call it 
> again, with a new LineCollection, dataLim is not re-set. If I comment 
> out the add_collection call, and just do the plot, then dataLim does get 
> reset when clear is called, so autoscale_view obviously doesn't work.
> 
> any ideas what's wrong? How would I force a re-set of dataLim?

It is not entirely clear to me what you mean by "call it again...", but 
note that autoscale_view() updates the viewLim from the dataLim; it does 
not update the dataLim.  That is done by add_line, which is called by 
plot, but it is not done by add_collection, as far as I can see.  The 
axes methods for updating dataLim are:

     def update_datalim(self, xys):
         'Update the data lim bbox with seq of xy tups'
         # if no data is set currently, the bbox will ignore it's
         # limits and set the bound to be the bounds of the xydata.
         # Otherwise, it will compute the bounds of it's current data
         # and the data in xydata
         self.dataLim.update(xys, not self.has_data())


     def update_datalim_numerix(self, x, y):
         'Update the data lim bbox with seq of xy tups'
         # if no data is set currently, the bbox will ignore it's
         # limits and set the bound to be the bounds of the xydata.
         # Otherwise, it will compute the bounds of it's current data
         # and the data in xydata
         #print type(x), type(y)
         self.dataLim.update_numerix(x, y, not self.has_data())

Eric