matplotlib-users

[Matplotlib-users] trace a rectangle

[Humufr <hu...@ya...>]

             Hi,

I have a problem to draw a rectangle:

The first is that I can't arrive to draw a rectangle with ipython 
-pylab, the script who work when it's launch independantly is not 
working interactively. The rectangle is not draw. Perhaps it's normal 
but I don't think.

The second problem I have is to draw a rectangle at a certain position 
with certain height and width. It's seems (at least when I tried to use 
it) that the position must be done relatively at the window and not from 
the plot. It's not very convenient because if I have a plot draw between 
1 and 100 in x and y, to draw the rectangle I add to use something 
between 0 and 1 so I had to rescale the rectangle.

Thanks,

    Nicolas

Re: [Matplotlib-users] trace a rectangle

[Humufr <hu...@ya...>]

             Hi,
 so I found some answer to the second problem, to draw a rectangle at a 
certain place you add to define  the limit for gca instance, by default 
the limit of the figure are not use:

from pylab import *
from matplotlib.patches import Rectangle
ax = gca()
set(gca(),'xlim',[0,10],'ylim',[0,10])
p = Rectangle((1,1),3,3,fill=False)
ax.add_patch(p)

or more pythonic:

from pylab import *
from matplotlib.patches import Rectangle
ax = gca()
ax.set_xlim([0,10])
ax.set_ylim([0,10])
p = Rectangle((1,1),3,3,fill=False)
ax.add_patch(p)


but if you use axis only without redefine gca limit that don't work:

from pylab import *
from matplotlib.patches import Rectangle
axis([0,10],[0,10])
ax = gca()
p = Rectangle((1,1),3,3,fill=False)
ax.add_patch(p)

I understand that gca return an instance but perhaps that will be a good 
idea if by default that will use the axis of the courrant figure and not 
[0,1,0,1].

Thanks,

          Nicolas

Humufr wrote:

>             Hi,
>
> I have a problem to draw a rectangle:
>
> The first is that I can't arrive to draw a rectangle with ipython 
> -pylab, the script who work when it's launch independantly is not 
> working interactively. The rectangle is not draw. Perhaps it's normal 
> but I don't think.
>
> The second problem I have is to draw a rectangle at a certain position 
> with certain height and width. It's seems (at least when I tried to 
> use it) that the position must be done relatively at the window and 
> not from the plot. It's not very convenient because if I have a plot 
> draw between 1 and 100 in x and y, to draw the rectangle I add to use 
> something between 0 and 1 so I had to rescale the rectangle.
>
> Thanks,
>
>    Nicolas

Re: [Matplotlib-users] trace a rectangle

[John H. <jdh...@ac...>]

>>>>> "Humufr" == Humufr  <hu...@ya...> writes:


    Humufr> but if you use axis only without redefine gca limit that
    Humufr> don't work:

    Humufr> from pylab import * from matplotlib.patches import
    Humufr> Rectangle axis([0,10],[0,10]) ax = gca() p =
    Humufr> Rectangle((1,1),3,3,fill=False) ax.add_patch(p)

I think you screwed up the "axis" syntax.  What you mean (I think) is:

    from pylab import *
    from matplotlib.patches import Rectangle
    axis([0,10,0,10])
    ax = gca()
    p = Rectangle((1,1),3,3,fill=False)
    ax.add_patch(p)
    show()

    Humufr> I understand that gca return an instance but perhaps that
    Humufr> will be a good idea if by default that will use the axis
    Humufr> of the courrant figure and not [0,1,0,1].

I'm a little confused here.  gca returns the current axes (note axis
and axes are different commands and have different meanings).  The
default axes is

2 >>> ax = gca()
 
3 >>> ax.get_position()
Out[3]: [0.125, 0.10999999999999999, 0.77500000000000002, 0.79000000000000004]

Can you clarify your meaning?  axis set the view limits of the current
axes.  The view limits are in data coordinates, and these are the same
limits that are controlled by xlim and ylim.  axes sets the position
of the axes (the frame in which your plots are made) and these
coordinates are in figure coords -- 0,0 is lower left of the figure
and 1,1 is upper right.

JDH

Re: [Matplotlib-users] trace a rectangle

[Humufr <hu...@ya...>]

John Hunter wrote:

>>>>>>"Humufr" == Humufr  <hu...@ya...> writes:
>>>>>>            
>>>>>>
>
>
>    Humufr> but if you use axis only without redefine gca limit that
>    Humufr> don't work:
>
>    Humufr> from pylab import * from matplotlib.patches import
>    Humufr> Rectangle axis([0,10],[0,10]) ax = gca() p =
>    Humufr> Rectangle((1,1),3,3,fill=False) ax.add_patch(p)
>
>I think you screwed up the "axis" syntax.  What you mean (I think) is:
>
>    from pylab import *
>    from matplotlib.patches import Rectangle
>    axis([0,10,0,10])
>    ax = gca()
>    p = Rectangle((1,1),3,3,fill=False)
>    ax.add_patch(p)
>    show()
>  
>

yes sorry I did mistake in my mail but the result is the same. I can't 
draw the rectangle where I want. To do this I had to set the xlim and 
ylim manually.

>    Humufr> I understand that gca return an instance but perhaps that
>    Humufr> will be a good idea if by default that will use the axis
>    Humufr> of the courrant figure and not [0,1,0,1].
>
>I'm a little confused here.  gca returns the current axes (note axis
>and axes are different commands and have different meanings).  The
>default axes is
>
>2 >>> ax = gca()
> 
>3 >>> ax.get_position()
>Out[3]: [0.125, 0.10999999999999999, 0.77500000000000002, 0.79000000000000004]
>
>Can you clarify your meaning?  axis set the view limits of the current
>axes.  The view limits are in data coordinates, and these are the same
>limits that are controlled by xlim and ylim.  axes sets the position
>of the axes (the frame in which your plots are made) and these
>coordinates are in figure coords -- 0,0 is lower left of the figure
>and 1,1 is upper right.
>  
>

I understand your point but I think that to draw on object inside a 
figure, using some relative coordinate are not very convenient. You add 
to play with the data coordinates and the figures coordinates. That can 
be useful for some objects but very often some people would like to plot 
a rectangle (or what do you want) with the data corrdinate and it's very 
disturbing at the beginning the way that patches is working.
I don't know if I'm clear this time (my english is very poor sometimes).

Thanks,

    Nicolas

Re: [Matplotlib-users] trace a rectangle

[John H. <jdh...@ac...>]

>>>>> "Humufr" == Humufr  <hu...@ya...> writes:

    Humufr> I understand your point but I think that to draw on object
    Humufr> inside a figure, using some relative coordinate are not
    Humufr> very convenient. You add to play with the data coordinates
    Humufr> and the figures coordinates. That can be useful for some
    Humufr> objects but very often some people would like to plot a
    Humufr> rectangle (or what do you want) with the data corrdinate
    Humufr> and it's very disturbing at the beginning the way that
    Humufr> patches is working.  I don't know if I'm clear this time
    Humufr> (my english is very poor sometimes).

Yes, apparently there is something of a language barrier -- my french
is not so good either, sigh.  

But I just want to reiterate, you are not using relative coords for
the rectangle in the example below.  When you do the following,

    from pylab import *
    from matplotlib.patches import Rectangle
    ax = gca()
    p = Rectangle((1,1),3,3,fill=False)
    ax.add_patch(p)

your rectangle is in *data coordinates* and it is where it should be
(center at 1,1 and width=height=3).  The problem is that your axis
"view" limits are not set properly (if you use the pan and zoom
features of the toolbar to move your view limits you'll see the
rectangle where it should be.  Only the plot commands (plot, scatter,
etc,....) call autoscale_view to set the view limits (add_patch does
not), so you need to set the axis limits yourself.

  axis([0,10,0,10])

In summary, the rectangle is being added in the right coordinate
system (data coords) but the view limits are not automatically
autoscaled unless you issue a plot command.  I choose not to do
autoscale every time a patch is added for performance reasons -- if
you are savvy enough to call add_patch, I assume you are savvy enough
to call set_xlim or set_ylim as appropriate for your data.


JDH

Re: [Matplotlib-users] trace a rectangle

[Jochen V. <vo...@se...>]

Hello John,

On Thu, Jan 20, 2005 at 02:07:26PM -0600, John Hunter wrote:
>     p =3D Rectangle((1,1),3,3,fill=3DFalse)
>     ax.add_patch(p)
>=20
> your rectangle is in *data coordinates* and it is where it should be
> (center at 1,1 and width=3Dheight=3D3).

I think this is wrong.  The lower-left corner is at (1,1), not
the center.  At least help(Rectangle) states

 |  __init__(self, xy, width, height, **kwargs)
 |      xy is an x,y tuple lower, left
 |     =20
 |      width and height are width and height of rectangle
 |     =20
 |      fill is a boolean indicating whether to fill the rectangle

All the best,
Jochen
--=20
http://seehuhn.de/