Designer pen tool perfect arc

[Juc1]

Hi all

With the node tool I can drag on a straight line to create an arc but is there a way to make the resulting arc perfectly symmetrical rather than being skewed left or right? I can get close by manually estimating where the midpoint is but is there a way to make it mathematically perfect?

 

[NathanC]

Hi @Juc1,

Looks like this has been previously requested in the feature requests and suggestions linked below, it does reference a workaround by dropping a node anywhere along the curve, highlighting the nodes and using the space horizontally/vertically alignment tools.

 

 

[NotMyFault]

1 hour ago, Juc1 said:

Hi all

With the node tool I can drag on a straight line to create an arc but is there a way to make the resulting arc perfectly symmetrical rather than being skewed left or right? I can get close by manually estimating where the midpoint is but is there a way to make it mathematically perfect?

 

 

There are multiple possible workaround:

• Activate snapping for nodes and/or grid
• add helper objects (e.g. 2 rectangles)
• add rulers to mark position of middle node
• Create only half of curve, then copy and flip, merge curves
• create a symbol (designer) of half a curve, then copy, flip and move symbol to create full curve

[R C-R]

2 hours ago, NotMyFault said:

There are multiple possible workaround:

• Activate snapping for nodes and/or grid
• add helper objects (e.g. 2 rectangles)
• add rulers to mark position of middle node

I do not see how activating snapping for nodes & or grid would help to make a perfectly symmetrical arc or how a ruler (a guide or something else?) would help, particularly if the idea is to avoid adding a third node.

Can you explain more about how this would work?

[NotMyFault]

1 hour ago, R C-R said:

I do not see how activating snapping for nodes & or grid would help to make a perfectly symmetrical arc or how a ruler (a guide or something else?) would help, particularly if the idea is to avoid adding a third node.

Can you explain more about how this would work?

Tested on iPad, same should be possible on desktop.

• Add a guide at the mathematical middle point (x axis). To find middle point, create a rectangle, double, align horizontally, scale to match curve. Or calculate from values in transform panel.
• add a guide at the y axis 
• select node tool
• grab the curve exactly at the intersection with the vertical guide
• drag down to the crossing of both guides

 

[R C-R]

24 minutes ago, NotMyFault said:

Add a guide at the mathematical middle point (x axis). To find middle point, create a rectangle, double, align horizontally, scale to match curve. Or calculate from values in transform panel.

If the 2 node straight line is not already centered on the document both vertically & horizontally, how would this work? Also, from your video, you seem to be adding a 3rd node to the line. Is that necessary?

[JimmyJack]

Just make sure Construction Snapping is turned on in the Node tool.
Adjust the bezier handles. The onscreen prompts will tell you when you're equal.
You don't have to be horizontal or vertical or centered. No need for midpoints, guides, grids or extra objects. Not that there's anything wrong with any of that 🙂.... sometimes midpoints come in handy. Just sayin'.

(most of the time the indicators show up together as in the pic below, but occasionally I've had to do one thing then the other. IOW get the angle first, release mouse, then click again to get the length hashes to show.) Edit: strike, that reverse it. Guess I got lucky on this example. Most of the time it's a one two punch. Still super easy. And yes to @R C-R's comment below.... hold shift when doing the length part. But, unlike his comment below, it's pretty darn responsive for me 🤔.

[R C-R]

1 hour ago, Hens said:

Using only a horizontal guide with the nodetool.
Hold shift and drag handles of both left and right node to snap to the guide.

Like with what @NotMyFault suggested, does this work if the 2 node line is not centered in the document?

1 hour ago, JimmyJack said:

Just make sure Construction Snapping is turned on in the Node tool.
Adjust the bezier handles. The onscreen prompts will tell you when you're equal.

That works for me to get equal angles but it is very hard to find exactly where to drag the node handles for those angle indicators to appear, mostly I think because there is a short delay before they appear after I finally find that exact spot on the canvas. So it ends up being a clumsy repetitive drag, pause, drag again procedure. If the delay was much shorter it would work much better.

Also, after I find that spot & move the node handle to it, to get the equal length hash marks to appear & the dragged node handle to snap to the equal length position, I have to hold down the Shift key. Otherwise the hash marks do not appear. I can't find a way to get both the angle & hash mark indicators to appear at the same time.

All things considered, I think we need a faster, simpler way to adjust a curved line so it forms a perfectly symmetrical arc.

[Old Bruce]

17 hours ago, R C-R said:

All things considered, I think we need a faster, simpler way to adjust a curved line so it forms a perfectly symmetrical arc.

Replace the straight line with an Ellipse or Pie and match the rotation and width. Then when happy convert to Curve and delete the bits you don't want/need.

[R C-R]

32 minutes ago, Old Bruce said:

Replace the straight line with an Ellipse or Pie and match the rotation and width. Then when happy convert to Curve and delete the bits you don't want/need.

That is a lot of steps for something that should be simple, quick, & easy to do on an existing shape, not just a straight or already curved line but also to make any shape symmetrical across any axis. For good reasons, that is a frequently requested feature.

[R C-R]

19 hours ago, JimmyJack said:

And yes to @R C-R's comment below.... hold shift when doing the length part. But, unlike his comment below, it's pretty darn responsive for me 🤔.

What OS & computer are you using? My iMac (specs in my sig) is reasonably powerful but I still have to hold the node I am dragging still for a moment before any of the construction snapping indicators appear. That makes it very hard to find the spot where that kicks in. The only exception to this is the single 90° indicator that appears when the drag creates a 90° angle between the 2 nodes. That one appears with almost no delay, even when I am still dragging the node.

[JimmyJack]

Hmmm, I've got about half all that. I am up to a v11 OS (Big Sur) though, fwiw.
Metal is on and display is open GL.

23 hours ago, R C-R said:

but I still have to hold the node I am dragging still for a moment before any of the construction snapping indicators appear.

Then how do you know when/where to hold still if nothing has appeared yet??
The only "pause" I get is on the actual snap. Which is a good thing.
And, of course, I can't just go zipping by and expect the snap to capture me..... but I don't have to go super slow either. 

Pretty snappy: