Re: [matplotlib-devel] data cursor

[Antonio K. <ank...@gm...>]

Hi everybody,

I made some progress with my data plotting program.

now I have stumbled in a new problem:  I want to be able to move the
data cursor by pressing a key, say '.' to move right, ',' to move
left.  I thought I was smart enough and added a method to the
DataCursor class:

    def moveto(self, event, ind):
        """
        """
        event.xdata = self.t[ind]
        event.ydata = self.y[ind]
        self.xstr = '%1.3f'%event.xdata
        self.ystr = '%1.3f'%event.ydata
        print event.xdata, event.ydata, event
        print self.xstr, self.ystr, event
        Cursor.onmove(self, event)

the event is caught in the main loop and sent of DataCursor.moveto

however, the cursor does not move at the end of this method as I had
hoped for.  I suspect the reason is the reason is that this method is
getting a keyEvent, not a mouseEvent and then onmove doesn't like it.
the original Cursor class looks for mouseEvents, not for keyEvents.
What should I do?  Is there a way to translate a keyEvent into a mouse
event, so I can fool the Cursor class?  another more elegant solution?

Also, after I hit '.' or ',' the cursor goes off.  I can turn it back
on hitting 1 and 2.

I attach a sample test code that uses essentially John's original code
plus this modification.

cheers

Antonio

Antonio Kanaan
Departamento de Fisica - Universidade Federal de Santa Catarina
CP 476 --  CEP 88040-900  --  Florianopolis  --  SC  --  Brasil
http://www.astro.ufsc.br/~kanaan   e-mail: ka...@as...
Phone: 55,48,33319069                       FAX  : 55,48,33319946

moveto is called from the main loop when I hit either '.' or ','

On 2/26/07, John Hunter <jd...@gm...> wrote:
> On 2/26/07, Antonio Kanaan <ank...@gm...> wrote:
> > Hi folks,
> >
> > I am planning to re-write a data viewer program I wrote ages ago using C + Xlib.
> >
> > This program allows me to plot on the same window several graphs (time
> > versus brightness - I work on variable stars).  They all share the
> > same independent variable (time passes the same for everybody).
> >
> > I can scroll and zoom the graphs both in X and Y.  When I scroll/zoom
> > in X all plots suffer the same action.  Y scrolling/zooming may be
> > done for each plot.
> >
> > Now the question: I need a data cursor, by that I mean some marker
> > that sits on top of a point and which may be moved forward/backward by
> > pressing a key.  Matplotlib has a mouse cursor that gives me the
> > cursor coordinates, but it doesn't
>
> This isn't too bad actually -- you can subclass the existing Cursor
> class to override the xdata and ydata atrributes to insure that the
> cursor sits only on your data points.  The example below uses the
> cursor class to overrride the toolbar formatting, and shows you how to
> toggle the visibility of multiple cursors in multiple axes with shared
> x axes.  I'll also attach it in case the mail system mangles the
> newlines.  Take a look at the MultiCursor in
> the widgets module, you might be able to do a similar trick there to
> have common x cursoring across multiple axes.
>
> from pylab import figure, show, nx
> from matplotlib.widgets import Cursor
>
> class DataCursor(Cursor):
>     def __init__(self, t, y, ax, useblit=True, **lineprops):
>         Cursor.__init__(self, ax, useblit=True, **lineprops)
>         self.y = y
>         self.t = t
>         self.xstr = ''
>         self.ystr = ''
>
>     def onmove(self, event):
>         """
>         we override event.xdata to force it to snap-to nearest data
>         item here we assume t is sorted and I'll use searchsorted
>         since it is a little faster, but you can plug in your nearest
>         neighbor routine, eg to grab the closest x,y point to the
>         cursor
>         """
>         xdata = event.xdata
>         ind = nx.searchsorted(self.t, xdata)
>         ind = min(len(self.t)-1, ind)
>         event.xdata = self.t[ind]
>         event.ydata = self.y[ind]
>         self.xstr = '%1.3f'%event.xdata
>         self.ystr = '%1.3f'%event.ydata
>         Cursor.onmove(self, event)
>
>     def fmtx(self, x):
>         return self.xstr
>
>     def fmty(self, y):
>         return self.ystr
>
> fig = figure()
> ax1 = fig.add_subplot(211)
> ax2 = fig.add_subplot(212, sharex=ax1) # connect x pan/zoom events
>
> t = nx.cumsum(nx.rand(20))
> s1 = nx.mlab.rand(len(t))
> s2 = nx.mlab.rand(len(t))
>
> ax1.plot(t, s1, 'go')
> ax2.plot(t, s2, 'bs')
> ax1.set_title("Press 1 for upper cursor and 2 for lower cursor")
> cursor1 = DataCursor(t, s1, ax1, useblit=True, color='red', linewidth=2 )
>
> # we'll let the cursor do the toolbarformatting too.
> ax1.fmt_xdata = cursor1.fmtx
> ax1.fmt_ydata = cursor1.fmty
>
> cursor2 = DataCursor(t, s2, ax2, useblit=True, color='red', linewidth=2 )
> ax2.fmt_xdata = cursor2.fmtx
> ax2.fmt_ydata = cursor2.fmty
>
>
> # now we'll control the visibility of the cursor; turn off cursor2 by default
> cursor2.visible = False
>
> def keyevent(event):
>     cursor1.visible = event.key=='1'
>     cursor2.visible = event.key=='2'
>     fig.canvas.draw()
>
> fig.canvas.mpl_connect('key_press_event', keyevent)
> show()
>
>
> >
> > - sit on top of my points and therefore doesn't give me the exact
> > value of that point
> > - allow me to move from one point to the next
> > - allow me to change which graph I want the cursor sitting on
> >
> > I thought of drawing my own cursor, deleting it and moving to the next
> > point . It seems this would take forever as (far as I understand)
> > matplotlib will redo the entire plot each time I do this.
> >
> > How hard is it for the developers to include a built in data cursor in
> > a similar fashion to the mouse cursor now available.  I am affraid
> > this isn't too easy, I don't know any plotting program that has one
> > like what I need.
> >
> > thanks for your attention,
> >
> > Antonio Kanaan
> >
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