Question

I am plotting some scalar data as a contour plot with matplotlib.contourf. On top of it, I am plotting some vector data with matplotlib.arrow. The basic plot has come along OK, but now I need to put a box on the plot with a default-size arrow plus the data value to which it corresponds, so the viewer will know what kind of scale he is looking at. For instance, I need a box with a horizontal arrow of some length and, below that, some text like “10 cm/sec”.

First, if anyone can give me a simple approach to this, I would be grateful.

Second, the approach I have tried is to do the contour plot, then plot the arrows, then add a rectangle to the plot like so:

rect=pl.Rectangle((300,70),15,15,fc='white')
pl.gca().add_patch(rect)

and then, finally, put my scale arrow and text on top of this rectangle.

This isn’t working because the rectangle patch covers up the contour, but it doesn’t cover up the arrows in the plot. Is there a way to move the patch completely “to the front” of everything else?

Answer 1

Got it. Using pylab.quiver and pylab.quiverkey functions. quiver produces a nice vector field with just a few lines of code, and quiverkey makes it easy to produce a scaling vector with text. And, for some reason, the arrows plotted with quiver are indeed covered by my rectangle, so it is easy to make the scaling arrow very visible. There are still some mysteries in all of this for me. If anyone wants to try to clear them up, would be much obliged. But I have a way now to do what I need in this instance.