Polar Contour

[cdhainaut]

Hi everyone,

I am looking for a possibility to do polar contour plots with plotly.
I saw this was mentioned in this topic already by @rafa-guedes : #2024
But I need a more complete solution.
The ideal contour plot I want should look like this:

If I use the method described in the post I mentioned, this gives me this result:

Which isn't matching enough the level of details I want to have.

Do you have an idea of a workaround I could use to achieve the target ?

Thanks

Cheers

[empet]

@carlitador
Polar Contour plot can be defined in a similar way as a rectangular (quadratic) one, but invalidating z-values outside a disk.
Let us suppose we have z-data stored in an array of shape (n, n). To plot its polar contour proceed as follows:

• define:

x = np.linspace(-r, r, n)  #r =disk radius
X, Y = np.meshgrid(x, x)
z[np.where(X**2+Y**2>r**2)] = np.nan   
fig=go.Figure(go.Contour(x=x, y=x, z=z, colorscale="balance", line_width=0.5,
                         contours=dict(start=np.nanmin(z),  end=np.nanmax(z), size=0.3)))
fig.update_layout(width=600, height=600,
                             template="none", xaxis_visible=False, yaxis_visible=False)
fig.show()

The above plot was defined from a npy file storing my z-data having np.nan outside the disk, centered at 0 and of radius 2, i.e:

z = np.load("circular-data.npy", allow_pickle=True) #https://github.com/empet/Datasets/blob/master/circular-data.npy
x = np.linspace(-2,  2,  420)
fig=go.Figure(go.Contour(x=x, y=x, z=z, colorscale="balance", line_width=0.5,
                         contours=dict(start=np.nanmin(z), end=np.nanmax(z), size=0.3)))
fig.update_layout(width=600, height=600,
                  template="none",xaxis_visible=False, yaxis_visible=False)

[cdhainaut]

Hi @empet,
Its a good idea of a workaround. However, I need to have the radius and angle ticks and axis appearing on the chart. Any idea of how to include that properly ?

Thanks

[empet]

@carlitador
For contour it is sufficient to plot the radius marking the angle 0, more radii cover the contour information. To display angles in degrees, as annotations, see this old tutorial and adapt it to the Plotly 4.14:
https://chart-studio.plotly.com/~empet/14803. You can also set customdata for your contour; consisting in r=np.sqrt(X**2+Y**2), and theta=np.arctan2(Y, X)*180/np.pi. Then define hovertemplate, i.e a string containing description of the hover text for each point in your contour: https://chart-studio.plotly.com/~empet/15366.

[gvwilson]

Hi - we are trying to tidy up the stale issues and PRs in Plotly's public repositories so that we can focus on things that are still important to our community. Since this one has been sitting for several years, I'm going to close it; if it is still a concern, please add a comment letting us know what recent version of our software you've checked it with so that I can reopen it and add it to our backlog. Thanks for your help - @gvwilson