2010/9/7 Guillaume Chérel <guillaume.c.che...@gmail.com>
> Hello,
>
> I'm trying to draw circles with the scatter function. They are supposed
> to represent trees in the savannah. It is thus important that they are
> displayed with a proper size, that is, one which represents their actual
> size on the field. After quite some confusion, I've found out (I think)
> that the size argument one can specify with the scatter function is
> given as a disk's surface in pixels square (I think that's what means
> the "points^2" in the documentation and from my own tests)
>
> What I would like is to give a surface in unit^2, where "unit" is the
> unit of my data, and which you can read on the plot's axes ticks. For
> example, each tree has coordinates like x=3500, y=2210. (The unit here
> is centimeters but we don't really need to know this). Say I want to
> draw a tree which canopy is 200 cm wide. That makes a disk which radius
> is 100, or surface 100^2*PI. How can I draw this?
>
> Many thanks,
> Guillaume
>
>
>
Guillaume,
Using scatter is probably not the way to go about what you want. The
circles for scatter are a fixed size and if you zoom in, they will not scale
accordingly.
You probably want to create patches of Circles:
http://matplotlib.sourceforge.net/api/artist_api.html#matplotlib.patches.Circle
http://www.mail-archive.com/matplotlib-users@lists.sourceforge.net/msg06786.html
Or even utilize a collection of Circles:
http://matplotlib.sourceforge.net/api/collections_api.html#matplotlib.collections.CircleCollection
Note that for a CircleCollection, you would use 'offset' to indicate the
center of each circle. After creating the collection, you would then use
ax.add_collection() function to add that collection to the axes.
I hope that is helpful.
Ben Root
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