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Accurate rounded curved line

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I just want to create a curved line with an accurately input radius (i.e. just the curved corner of a rounded rectangle) and move it around.


How to I do this? I'm not very good at moving the bezier handles so just want to draw a line and then input a curve value for the radius to get a smooth rounded curve. Is this possible yet?



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Here is a process that you can use to get a perfect 1/4 circle curve with the exact radius you want. It’s a little long winded but it is still good to know.


1. Using the circle tool draw a circle of any good size holding down the shift key to keep it circular.

2. Select the “Move Tool” and highlight the circle.

3. Go to the tool bar area and select “Convert to Curves”.

4. Now grab the “Node Tool” and click on the circle to highlight it.

5. Click on the 12:00 node and select “Action: Break Curve”.

6. Repeat this process on the 3:00 node. This effectively makes the upper right quarter of the circle an independent separate arc segment.

7. Deselect the entire circle so no nodes are highlighted then click on the upper right section and you will only see two node selected.

8. With those two nodes selected and still using the node tool drag a rectangle around the entire upper right section to select both the 12:00 and the 3:00 node.

9. Now placing the node tool cursor on one the of the two highlighted nodes you can drag that section away as an individual arc without it reshaping.


Now for setting the radius you want.


1. Select the “Move Tool” and highlight the arc.

2. Look in the “Transform” area at the bottom right and notice the W: (width) and the H: (height) values.

3. Simply enter into both fields the exact radius you want and you are done.


You now have a perfect arc segment with an exact radius. You can duplicate it, flip it, rotate it or whatever you need to do.


Although this seems like a rather complicated procedure I just timed my self doing exactly the above and did it all in 26.43 seconds.


The main idea here is two fold. One to get a perfect 1/4 arc and the second to learn a little about using the “Action: Break Curve” and also to show how to move an entire object by any one node.


A nice (maybe byproduct of AD) is that once you have a path selected with the node tool you can then drag a selection rectangle completely around that path and select every node on the path at one time, without it selecting any other object, but that you can also drag it by any node without modifying the shape of the path. This lets you snap a single node to any other object.


Hope this is helpful if not long winded (something I am known for).



OS X Ventura 13.0.1, Mac Studio M1 Max, 27" Apple Studio Display, 32 GB SSD. Affinity Universal License for 2.0.

Mac User & Programmer since 1985 to date. Author of “SignPost” for vinyl sign cutting.

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Great that you found it works. Like I said, it is not the quickest approach at the moment but it does work and is not that hard once you understand what you are actually doing by cutting the paths and how to do it.


Also. Like Dave said, you can also use the same approach when starting from different predefined shapes like the Pie shape or rounded Rectangles, Stars, etc. Once they are converted to paths the exact same techniques apply equally.


Glad I could help. I think the guys a Serif needed to get AD to market so they could start to get a ROI and they started with a very solid product. Up until release all the money was flowing outward. Now the tide has turned and they will be off and running. Now that they have a solid base aI think we are going to see lots of little improvements and additions that will only enhance the experience of all AD users and make graphics a lot easier too.



OS X Ventura 13.0.1, Mac Studio M1 Max, 27" Apple Studio Display, 32 GB SSD. Affinity Universal License for 2.0.

Mac User & Programmer since 1985 to date. Author of “SignPost” for vinyl sign cutting.

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  • 4 years later...
On 10/10/2014 at 8:24 PM, MEB said:

You can do that currently for rounded rectangles, but not for other shapes.

Affinity team is improving this so expect some news soon.

Has anything been actioned here?

Not the OP's specific request but I too simply want to create line + curve vectors but precisely.

i.e. create a line with the pen tool and completely control curves made from it.

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