Contour Plots and Points

Question

Why can I not have a single point on a contour plot?

var('x,y')

f(x,y)=sin(x)*cos(y)

G = contour_plot(f(x,y),(x,-3,3),(y,-3,3),contours=20,plot_points=100)

G += point((1,1), size=100) 

G.show()

does not display the point. I can add a line (for example)

G += line(((1.5,1),(1.5,0)))

and that line shows up but not the point.

Thanks.

JT

Accepted Answer

The point is there -- it's simply lurking behind the contour plot. Or, in matplotlib jargon (one of the plotting packages Sage uses is called matplotlib), it doesn't have a higher zorder. The zorder is the layer level, where the layers are drawn from lower to higher.

I can never remember what zorders different things default to, but it's usually easily changed manually:

var('x,y')
f(x,y)=sin(x)*cos(y)
G = contour_plot(f(x,y),(x,-3,3),(y,-3,3),contours=20,plot_points=100)
G += point((1,1), size=100,zorder=2)
G.show()

produces

image description

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Thanks.

Just to be certain, why does subsequently plotting a line without a zorder not put that line behind the contour plot as well?

link

posted Jan 16 '12

travis
23 ● 5
http://math.mc.edu/travis

Unfortunately I don't understand the order in which things are drawn well enough to say what the order is when zorders aren't specified/things have the same zorder. Note that you can use the ".set_zorder" method on graphics objects to change it after-the-fact.

DSM (Jan 16 '12)

1

it seems to make sense to have contour plots below other things generally. It would be great if someone came up with a comprehensive sensible default zorder for all of the graphics objects.

Jason Grout (Jan 16 '12)

Agreed. But who will take the responsibility for user complaints that that zorder setup is wrong?

kcrisman (Jan 17 '12)

the same person that does now...the user who wants to submit a patch.

Jason Grout (Apr 12 '12)

Contour Plots and Points

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