Draft Polygon Wiki

[C4e]

Hello.

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OS: macOS 10.16
Word size of FreeCAD: 64-bit
Version: 0.20.27770 (Git)
Build type: Release
Python 3.9.10, Qt 5.12.9, Coin 4.0.0, OCC 7.5.3
Locale: C/Default (C)
Installed mods: 
  * Reporting
  * dodo
  * DynamicData 2.38.0
  * Plot
  * parts_library
  * fcgear 1.0.0
  * 3D_Printing_Tools
  * Assembly4 0.11.10

I came from a discussion about knife bend sharpeners to the Draft_Polygon entry.

In the Part Design Workbench a polygon is made by clicking the center point and the circumference point.

In the Draft Workbench a polygon is made the same way. The Draw Mode Property is set to inscribed. If I change it to circumscribed, the size of the polygon raises.

Can anybody please check this and the article please.

[chrisb]

This looks alright to me. For a given radius the inscribed polygon is naturally smaller than the circumscribed.

[onekk]

Probably terminology is important.

I've used these pages on my early steps in geometry (sadly my school rememberings where very bad in maths)

https://www.mathopenref.com/polygonincircle.html

https://www.mathopenref.com/polygoncircumcircle.html

https://www.mathopenref.com/apothem.html

https://www.mathopenref.com/polygonradius.html

radius, apothem and related formulas were rather obscure in mi mind .

Sorry if this is OT.

Regards

Carlo D.

[C4e]

This looks alright to me. For a given radius the inscribed polygon is naturally smaller than the circumscribed.

Just take a closer look please. I draw a polygon, its default draw mode is described as inscribed. When I changed the property to circumscribed, its size raises.

See https://en.wikipedia.org/wiki/Circumscribed_circle and https://en.wikipedia.org/wiki/Inscribed_figure

The FreeCAD wiki figure shows to clicks (1. center, 2 on circumference). But the property says inscribed. The radius of the inscribed figure is not the the same as the circumference radius. And if the second click is on the circumference, this is not possible.

[kisolre]

The relation inscribed/circumscribed is poligon -> circle. So the poligon is inscribed IN a circle OR poligon is circumscribed AROUND a circle. Not the other way around. At least that is my understanding.

[Roy_043]

... And that is pretty much what the Draft Polygon page says:

Draw Mode (Enumeration): specifies if the polygon is inscribed in a circle or circumscribed around a circle.

[Roy_043]

Maybe move this to the Wiki forum?

[chrisb]

I still cannot see the point. Look at this image ...

SnipScreenshot-4e7343.png (26.83 KiB) Viewed 1390 times

... it shows a circle with a radius of 50mm and two draft polygons, both having a radius of 50mm too. One of them is inscribed, which means that its vertices lie on the circle the other is circumscribed, which means that the lines are tangent to the circle.
The former is the biggest regular polygon inside of the circle, the latter is the smalles outside of the circle.

[chrisb]

Maybe move this to the Wiki forum?

Done. (Although this seems to be rather a help request. It was definitely wrong in Open discussion.)

[C4e]

Thank you for your feedback. I probably got caught up in a misunderstanding.