17 Oct 2008 19:44

## limiting theta in polar axis plots

Is there any way to limit the theta extent in a polar axis plot?

There are a variety of angular contexts in which 360 degrees are not necessary.  To convey the orientation of an undirected line, you need only 0-180 degrees.  The minimum separation between two intersecting lines only ranges from 0-90 degrees.

It seems like the ideal way for this to work would be to have a function analogous to xlim(), maybe called thetalim(thetamin, thetamax), and then treat the two bounding radial lines as the primary and secondary y axes.

Didn't see anything like this in any of the examples or documentation though.  If it's not possible now, I think it would be a wonderful addition.

Thanks,
Zane

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Zane Selvans
Amateur Earthling
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17 Oct 2008 20:06

### Re: limiting theta in polar axis plots

```No, it's not possible now.  Just so I'm clear -- you're suggesting
plotting on a wedge from theta_1 to theta_2?  Seems doable with a little
work.

Mike

Zane Selvans wrote:
> Is there any way to limit the theta extent in a polar axis plot?
>
> There are a variety of angular contexts in which 360 degrees are not
> necessary.  To convey the orientation of an undirected line, you need
> only 0-180 degrees.  The minimum separation between two intersecting
> lines only ranges from 0-90 degrees.
>
> It seems like the ideal way for this to work would be to have a
> function analogous to xlim(), maybe called thetalim(thetamin,
> thetamax), and then treat the two bounding radial lines as the primary
> and secondary y axes.
>
> Didn't see anything like this in any of the examples or documentation
> though.  If it's not possible now, I think it would be a wonderful
>
> Thanks,
> Zane
>
> --
> Zane Selvans
> Amateur Earthling
> zane@... <mailto:zane@...>
> 303/815-6866
> http://zaneselvans.org
> PGP Key: 55E0815F
>
>
>
>
>
>
> ------------------------------------------------------------------------
>
> -------------------------------------------------------------------------
> This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
> Build the coolest Linux based applications with Moblin SDK & win great prizes
> Grand prize is a trip for two to an Open Source event anywhere in the world
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--

--
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA

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17 Oct 2008 20:40

### Re: limiting theta in polar axis plots

On Oct 17, 2008, at 11:06 AM, Michael Droettboom wrote:

No, it's not possible now.  Just so I'm clear -- you're suggesting plotting on a wedge from theta_1 to theta_2?  Seems doable with a little work.

Yes, exactly.  For instance if I wanted to make a polar bar chart showing the distribution of angles separating a collection of lines at their intersections, I would only need to display one quarter of the polar plot, the first quadrant, from 0-90 degrees.  If I wanted to display the orientation of, say, a fault on the surface of the Earth, I'd need 180 degrees, but I might want to use the northern half of the circle (orientations ranging from West to East (-90, 90)) or perhaps the eastern half (ranging from (0, 180)).

Ideally, the user would be able to specify both thetamin and thetamax, and also an offset describing the location of theta=0, because in some applications it doesn't make sense for zero to be in its traditional polar-coordinates location at the right hand side.  E.g. in a geographic context, where the angles being displayed are compass headings, it is traditional to put zero (north) at the top.  Putting zero at the top would also make sense if you were plotting data that corresponded to angular deviations to the left and right from some specified path.

Some portion of this functionality has been implemented in the "windrose" module, see:

but with a mind toward a particular kind of application (windrose diagrams obviously :).  But I think allowing users to specify (thetamin, thetamax, offset) would be a very generally applicable improvement.

Thanks again,
Zane

--
Zane Selvans
Amateur Earthling
303/815-6866
PGP Key: 55E0815F

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Gmane