I am using matplotlib
with NavigationToolbar2QT
. The toolbar is showing the position of the cursor. But I would like that the cursor snaps to the nearest data point (when close enough) or simply show the coordinate of nearest data point. Can that be somehow arranged?
The plt. axis() method allows you to set the x and y limits with a single call, by passing a list which specifies [xmin, xmax, ymin, ymax] : In [11]: plt.
You could subclass NavigationToolbar2QT
and override the mouse_move
handler. The xdata
and ydata
attributes contain the current mouse position in plot coordinates. You can snap that to the closest data point before passing the event to the base class mouse_move
handler.
Full example, with highlighting of the closest point in the plot as a bonus:
import sys
import numpy as np
from matplotlib.backends.qt_compat import QtWidgets
from matplotlib.backends.backend_qt5agg import FigureCanvas, NavigationToolbar2QT
from matplotlib.figure import Figure
class Snapper:
"""Snaps to data points"""
def __init__(self, data, callback):
self.data = data
self.callback = callback
def snap(self, x, y):
pos = np.array([x, y])
distances = np.linalg.norm(self.data - pos, axis=1)
dataidx = np.argmin(distances)
datapos = self.data[dataidx,:]
self.callback(datapos[0], datapos[1])
return datapos
class SnappingNavigationToolbar(NavigationToolbar2QT):
"""Navigation toolbar with data snapping"""
def __init__(self, canvas, parent, coordinates=True):
super().__init__(canvas, parent, coordinates)
self.snapper = None
def set_snapper(self, snapper):
self.snapper = snapper
def mouse_move(self, event):
if self.snapper and event.xdata and event.ydata:
event.xdata, event.ydata = self.snapper.snap(event.xdata, event.ydata)
super().mouse_move(event)
class Highlighter:
def __init__(self, ax):
self.ax = ax
self.marker = None
self.markerpos = None
def draw(self, x, y):
"""draws a marker at plot position (x,y)"""
if (x, y) != self.markerpos:
if self.marker:
self.marker.remove()
del self.marker
self.marker = self.ax.scatter(x, y, color='yellow')
self.markerpos = (x, y)
self.ax.figure.canvas.draw()
class ApplicationWindow(QtWidgets.QMainWindow):
def __init__(self):
super().__init__()
self._main = QtWidgets.QWidget()
self.setCentralWidget(self._main)
layout = QtWidgets.QVBoxLayout(self._main)
canvas = FigureCanvas(Figure(figsize=(5,3)))
layout.addWidget(canvas)
toolbar = SnappingNavigationToolbar(canvas, self)
self.addToolBar(toolbar)
data = np.random.randn(100, 2)
ax = canvas.figure.subplots()
ax.scatter(data[:,0], data[:,1])
self.highlighter = Highlighter(ax)
snapper = Snapper(data, self.highlighter.draw)
toolbar.set_snapper(snapper)
if __name__ == "__main__":
qapp = QtWidgets.QApplication(sys.argv)
app = ApplicationWindow()
app.show()
qapp.exec_()
If you are working with large sets of points, I advice you to use CKDtrees
:
import matplotlib.pyplot as plt
import numpy as np
import scipy.spatial
points = np.column_stack([np.random.rand(50), np.random.rand(50)])
fig, ax = plt.subplots()
coll = ax.scatter(points[:,0], points[:,1])
ckdtree = scipy.spatial.cKDTree(points)
I refactored kpie's
answer here little bit. Once ckdtree
is created, you can identify closest points instantly and various kind of information about them with a little effort:
def closest_point_distance(ckdtree, x, y):
#returns distance to closest point
return ckdtree.query([x, y])[0]
def closest_point_id(ckdtree, x, y):
#returns index of closest point
return ckdtree.query([x, y])[1]
def closest_point_coords(ckdtree, x, y):
# returns coordinates of closest point
return ckdtree.data[closest_point_id(ckdtree, x, y)]
# ckdtree.data is the same as points
Interactive display of cursor position. If you want coordinates of the closest point to be displayed on Navigation Toolbar:
def val_shower(ckdtree):
#formatter of coordinates displayed on Navigation Bar
return lambda x, y: '[x = {}, y = {}]'.format(*closest_point_coords(ckdtree, x, y))
plt.gca().format_coord = val_shower(ckdtree)
plt.show()
Using events. If you want another kind of interactivity, you can use events:
def onclick(event):
if event.inaxes is not None:
print(closest_point_coords(ckdtree, event.xdata, event.ydata))
fig.canvas.mpl_connect('motion_notify_event', onclick)
plt.show()
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With