How to draw 2d compass in 3d UIAxes

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Kurt
Kurt on 7 Apr 2023
Commented: Kurt on 11 Apr 2023
Is it possible to use the compass() function to draw a compass rose in a UIAxes object? I don't care about the function depicted by the compass, I just want the circles and degree text for other purposes. Here is my code:
function draw_compass(em)
th = linspace(0,.001,1000);
r = linspace(5000,384400,1000);
[u,v] = pol2cart(th,r);
pax = compass(em.UIAxes,u,v);
for i = 1:1000 % hide the arrows
pax(i).LineStyle = 'none';
end
end
If I run draw_compass() as a standalone function, it works just fine.
When I try to display this in my UIAxes, I get a "bowtie" effect from the hidden arrows, but no range circles or compass angle text. What gives?
I also tried polarplot(), but it doesn't like my Cartesian coordinate system. Also tried a flattened ellipse, but the range circles are uneven, and I would still have to add text for the angles.
If none of this works, I will have to hand-jam all the circles and radial lines and text the hard way.

Accepted Answer

Kevin Holly
Kevin Holly on 7 Apr 2023
Edited: Kevin Holly on 7 Apr 2023
It is possible to place the compass rose in a 3D uiaxes. Did you want to plot something in addition to this? If so, you may have difficulties if you try plotting a 3D scatter on top with scatter3.
ax = uiaxes;
th = linspace(0,.001,1000);
r = linspace(5000,384400,1000);
[u,v] = pol2cart(th,r);
compass(ax,u,v)
for ii = 1:length(ax.Children)
delete(ax.Children(1))
end
view(3)
  8 Comments
Kurt
Kurt on 10 Apr 2023
I found the problem. "hold" was set. If I call
hold(em.UIAxes,'off')
the compass appears.
I dug into the compass() code and found that it really just calls polar(), so I can probably use that instead.
This also explains why running the compass function standalone worked: hold was off by default.
Kurt
Kurt on 11 Apr 2023
Kevin made an important point earlier. If you plot underneath this compass, you won't be able to see your data. compass(), which is really based around plot(), is opaque and does not respond to alpha transparancy settings either. So, if you want a compass you can see through, you will need to create it yourself from scratch.

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