Question

I am plotting a scatter plot on a Basemap. However, the data with this scatter plot changes based on user input. I would like to clear the data (only the data — not the entire basemap figure) and re-plot new scatter points.

This question is similar but was not answered (http://stackoverflow.com/questions/8429693/python-copy-basemap-or-remove-data-from-figure)

Currently I am closing the figure with clf(); however, this requires me to re-draw the entire basemap and scatter plot together. On top of this, I am doing all of the redrawing inside of a wx panel. The basemap redraw takes too long and am hoping that there is an easy way to simply re-plot scatter points only.

#Setting up Map Figure 
self.figure = Figure(None,dpi=75) 
self.canvas = FigureCanvas(self.PlotPanel, -1, self.figure) 
self.axes = self.figure.add_axes([0,0,1,1],frameon=False) 
self.SetColor( (255,255,255) ) 

#Basemap Setup 
self.map = Basemap(llcrnrlon=-119, llcrnrlat=22, urcrnrlon=-64, 
                urcrnrlat=49, projection='lcc', lat_1=33, lat_2=45, 
                lon_0=-95, resolution='h', area_thresh=10000,ax=self.axes) 
self.map.drawcoastlines() 
self.map.drawcountries() 
self.map.drawstates() 
self.figure.canvas.draw() 

#Set up Scatter Plot 
m = Basemap(llcrnrlon=-119, llcrnrlat=22, urcrnrlon=-64, 
        urcrnrlat=49, projection='lcc', lat_1=33, lat_2=45, 
        lon_0=-95, resolution='h', area_thresh=10000,ax=self.axes) 

x,y=m(Long,Lat) 

#Scatter Plot (they plot the same thing) 
self.map.plot(x,y,'ro') 
self.map.scatter(x,y,90) 

self.figure.canvas.draw() 

Then I do an some type of update on my (x,y)…

#Clear the Basemap and scatter plot figures
self.figure.clf()

Then I repeat all of the above code. (I also have to redo my box sizers for my panel — I did not include these).

Thanks!

Answer 1

The matplotlib.pyplot.plot documentation mentions that the plot() command returns a Line2D artist which has xdata and ydata properties, so you might be able to do the following:

# When plotting initially, save the handle
plot_handle, = self.map.plot(x,y,'ro') 
...

# When changing the data, change the xdata and ydata and redraw
plot_handle.set_ydata(new_y)
plot_handle.set_xdata(new_x)
self.figure.canvas.draw()

I haven’t managed to get the above to work for collections, or 3d projections, unfortunately.