Circular hole in polygon

[Edwin Humphries]

Hi all

I'm mapping a property, currently doing the carpark. I've created a polygon for the outline, and holes for garden beds, using an underlying line layer to guide the vertices. One of the garden beds is circular, and the line layer has a circular feature, with innumerable vertices. How do I create a circular hole to match this, without having to select each of those vertices one-by-one?

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Regards,
Edwin Humphries
Mobile: 0435 672 457

I acknowledge the traditional Wodi Wodi custodians, their elders and customs, of the Dharawal lands on which I live.

"At every moment he beholdeth a wondrous world, a new creation, and goeth from astonishment to astonishment, and is lost in awe at the works of the Lord of Oneness."     Bahá'u'lláh
"... humans are interesting. With all the wonders there are in the Universe, they invented boredom."     Terry Pratchett, Hogfather
"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science. He to whom this emotion is a stranger, who can no longer pause to wonder and stand rapt in awe, is as good as dead: his eyes are closed."     Albert Einstein
"Stuff your eyes with wonder ... live as if you'd drop dead in ten seconds. See the world. It's more fantastic than any dream made or paid for in factories."     Ray Bradbury

[Ia...@jcis.net.au]

There is a You Tube video – Digitising Polygons with a hole https://www.youtube.com/watch?v=5X-eZQcCXyE&ab_channel=SpatialThoughts

 

That explains the process

 

Cheers

 

Dr Iain Stuart

JCIS Consultants

President Royal Australian Historical Society

P.O. Box 2397

Burwood North

NSW, 2134

 

(02) 9701 0191
(0413) 380116 (m)

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[Edwin Humphries]

Thanks Iain.

As I think I said in my original post, I have already created holes in the carpark polygon; these holes are irregularly shaped, and I used vertices from the underlying line layer to define both the polygon and the holes. So I'm familiar with the process.

But I have, in the line layer, a garden bed that is a perfect circle - and has many many vertices. I'm trying to work out how to add that shape precisely to as a hole in the polygon - preferably without selecting every vertex in the line layer.

Regards,
Edwin Humphries
Mobile: 0435 672 457

I acknowledge the traditional Wodi Wodi custodians, their elders and customs, of the Dharawal lands on which I live.

"At every moment he beholdeth a wondrous world, a new creation, and goeth from astonishment to astonishment, and is lost in awe at the works of the Lord of Oneness."     Bahá'u'lláh
"... humans are interesting. With all the wonders there are in the Universe, they invented boredom."     Terry Pratchett, Hogfather
"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science. He to whom this emotion is a stranger, who can no longer pause to wonder and stand rapt in awe, is as good as dead: his eyes are closed."     Albert Einstein
"Stuff your eyes with wonder ... live as if you'd drop dead in ten seconds. See the world. It's more fantastic than any dream made or paid for in factories."     Ray Bradbury

To view this discussion, visit https://groups.google.com/d/msgid/australian-qgis-user-group/000201db8258%24f9726bc0%24ec574340%24%40jcis.net.au.

[Juan Fernando Berrío]

Hello Edwin, 

When digitising or editing features, have you checked out the "snapping" option, and after that, the "enable tracing" option?  If you have a quick google at how to use them, they should be able to accomplish what you're trying to do.  

You can find snapping options in the main menu of QGIS, at the top of the window, under "Project".  There is also a "snapping" toolbar you can activate that has the relevant commands.  The "tracing" button shows up with a little yellow lightning on it, or you can activate it by pressing T on your keyboard while you're digitising something. 

Sometimes they don't behave the way you expect them to, especially if the base layer you're trying to snap to has little imperfections.  So it's ok to take your time to learn how to use them to do what you want them to. 

You can have a Google/YouTube on how to use them.  In case of questions, feel free to ask again. 

Hope it helps, 

Juan

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[Andrew Keith]

Hi Edwin,

This is how I'd do it:

1. Select the "Add Ring" tool.
2. From the "Shape Digitising toolbar", choose "Circle from 2 Points."
3. Left-click on a point on the circle you want to cut, then right-click on another point on the same circle.

If the Shape Digitising toolbar is not displayed, right-click on an empty space in the toolbar area and enable it from the menu.

The only other trick is that in my version of QGIS (3.28), I need to go to the "Digitising toolbar" and change from "Digitise with Shape" to "Digitise with Segments," otherwise, it stays in 2-point circle mode.

Thanks,

Andrew.