PreFigure Polar Coordinates

[Anansa Green]

Is there a way to set the coordinate system to polar in PreFigure? I can code concentric circles for the "grid" and parameterize all the things I want graphed, if necessary, but I wanted to see if there's a more elegant solution first. I couldn't find anything in the documentation or examples with polar coordinates.

[Rob Beezer]

Dear Anansa,

Unless somebody else knows, I'm sure David Austin will have an answer for you
soon, once he's back online.

Rob

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[David Austin]

Hi Anansa,

Those features don't yet exist, but what you're asking certainly seems reasonable.  Can you send a list of things that you'd like to see?  I've thought of log-log plots, but this could be similar and good to think about at the same time.

Thanks, 

David 

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[Anansa Green]

Hi David,

I have a working grid image so far (attached). I'm working on a pre-calculus text and was thinking of creating something similar to these two figures from the OpenStax text: Figure 8.4.20 and Figure 8.4.21.

Thanks,

Anansa

[David Austin]

That helps a lot so thanks for sending those.  I think we're on the same page.  I can also imagine that you or someone else would want to fill the area of a polar curve.  I'll put something together soon and let you know.

Thanks again,

David

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[David Austin]

Hi Anansa,

I've added some features for graphing in polar coordinates, which are described here:  Subsection 3.7.6: Polar coordinates.  I'm not sure what environment you're working in, but you will probably need to update your prefig installation (the PreFigure playground is always up to date though).  In a codespace or local installation, you can say "pip install --upgrade prefig" in a terminal to get version 0.3.1 of prefig.

Please let me know how this works for you.  I'm happy to make changes or additions if something can be improved.

Thanks,

David

On Mon, Jun 9, 2025 at 4:06 PM Anansa Green <anansa...@gmail.com> wrote:

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[Anansa Green]

I'm back! I thought I sent a very effusive thank-you message back in June, but apparently it was all in my head. It's been working beautifully, apart from one issue:

When plotting individual points with the <point> element and attribute @coordinates="polar" it seems the point is still plotting with rectangular coordinates.  Here's a copy/paste of my code and attached svg from the PreFigure Playground for reference:

<diagram dimensions="(600,600)" margins="0">

  <definition>r=2</definition>

  <definition>t=pi</definition>

  <coordinates bbox="(-5,-5,5,5)">

    <grid

      coordinates="polar"

      spacings="((0,.5,7),(0,pi/12,2*pi))"

      stroke="lightgray"

    />

    <grid

      coordinates="polar"

      spacings="((0,1,7),(0,pi/6,2*pi))"

      stroke="gray"

    />

    <axes

      hticks="(-5,1,5)"

      vticks="(-5,1,5)"

      hlabels="(-5,1,5)"

      vlabels="(-5,1,5)"

      clear-background="yes"          

    />

    <point

      coordinates="polar"

      p="(r,t)"

      clear-background="yes">

       <m>A</m>

      </point>

  </coordinates>

</diagram>

[David Austin]

Hi Anansa,

That doesn't work because I didn't think to do it!  Thanks for making this suggestion, which is now implemented and in the latest release.  I used your code in the Playground to make the image below (I included the attribute @offset="(0,2)" on the #point to move the label off the axis).  If you're working in a codespace or locally, you can update with "pip install prefig --upgrade".  I will update the documentation in 3.7.7 later today.

Just let me know if there's anything else that would be helpful.

Thanks again,

David

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