Joining end points...

[Edward_Goodwin]

Hello I wonder if someone can help me. See attached...

I have a shape (constructed from part of a circular plus two straight lines. Pretty simple. I've joined the straight lines to the circle so it's now a closed shape. However, I need to modify the straight lines (I will turn them into spline curves. However, as you can see in the attached, the node I will change is not a smooth join but a sharp join. Hence, when I move the spline handles a corner is created.

However, if I select to create a smooth curve or smart curve for that node, the overall shape changes.

What can I do to avoid this? I have to say that, in comparison with Illustrator, I find the line / node joining in AD(2) very confusing than AI... 😞

All thoughts gratefully received! Edward

[firstdefence]

What are you trying to achieve?

[Edward_Goodwin]

Hi firstdefence - thanks for the reply...

I'm need to adjust the straight lines (which form the bottom 'V') to be spline curves. This will then be translated into 3D CAD (unfortunately and very annoyingly you can't export dxf from Affinity but that's another story). 

But really, beyond what I'm trying to achieve here specifically, it's really the principle of the thing I'm after - i.e. how can I transform the sharp node (indicated in the second image) such that I can adjust the curves without a discontinuity? As you can see, I can't simply convert to smooth or smart (I want to retain the geometry of the top circular section). 

Out of interest, why is the node indicated shown red whereas the others are all blue?

Edward

[firstdefence]

32 minutes ago, Edward_Goodwin said:

Out of interest, why is the node indicated shown red whereas the others are all blue?

It's like a terminator node, it's where the curve/path is closed, there is also a red line that extends from it, this indicates the direction the curve was drawn in and you can click on the reverse button in the Pen and node tool context menu to see it change: https://affinity.help/designer2/English.lproj/pages/Tools/tools_node.html

[Edward_Goodwin]

Ok - thanks - I'll give the reverse button a try.

But do you have any thoughts about the reason for the question - i.e. the sharp-to-smooth change? Why is this particular node a sharp join whereas all the rest are constant curvature?

[loukash]

1 hour ago, Edward_Goodwin said:

What can I do to avoid this?

Enable "Perform construction snapping" – and other snapping options if necessary, make use of the Transform Mode and alignment handles while using the Node tool, general snapping options, guides, grids, etc. etc. Watch also the status bar for modifiers. There are many options.

See also affinity.help/designer2/English.lproj/pages/CurvesShapes/edit_linesAndShapes.html

So in your case, for example something like this:

 

 

[firstdefence]

27 minutes ago, Edward_Goodwin said:

Why is this particular node a sharp join whereas all the rest are constant curvature?

It's probably because it's a straight curve, so when you created the shape and used either straight curves drawn with the pen tool or used a shape such as the diamond or rectangle, it maintained the sharp node and extended a handle to allow the curvature of the ellipse to be maintained.

The problem is, when you change the sharp node to a smooth or a "not so" smart node, it distorts the curve above instead of maintaining its status quo. Even if you change the nodes of the diamond/rectangle shape to smooth or smart when you add/unite the curves at the point they intersect the nodes become sharp. I have no idea why this happens maybe it's a bug or there is an issue with joining curves.

 

[David in Яuislip]

Does this help or do I have wrong end of the stick?

Original shape in red, copy in green with reduced stroke width for visibility
Green centre nodes were sharp then converted to smooth
Left one modified per the close-up
Right one unchanged

[Edward_Goodwin]

Dear All,

Thank you so much for your full responses! It's very kind of you to take the time.

Loukash and David - the issue is not drawing the shape in the first place, it's modifying a shape that already exists... I want to be able to modify a shape which currently has a sharp node rather than a smooth node. Changing the node to a smooth node (annoyingly) changes the shape in ways that I don't want. That said, being better/cleverer about drawing the shape in the first place such as per Loukash's video does make sense. It's just annoying that when converting from one node to another actually changes the base shape; I don't see why.

firstdefence - I think you've understood the issue and, if I've understood correctly, you're saying that what I'd like to do isn't really possible. I think you're saying that the very nature of joining the node connected to a straight line means that it'll be sharp (even if the curve connected to it is, say, tangential. Is that correct? If so, that to me is a bit nuts... Hey ho.

Thank you again. If you do think of a way to do what I'm asking, then do drop me a line 🙂 in the meantime, have a good weekend one and all!

Edward

[loukash]

5 hours ago, Edward_Goodwin said:

Loukash and David - the issue is not drawing the shape in the first place, it's modifying a shape that already exists... I want to be able to modify a shape which currently has a sharp node rather than a smooth node. Changing the node to a smooth node (annoyingly) changes the shape in ways that I don't want.

I got that, of course. My example is just an example which tools you can use in such scenario. And there are other methods as well. Be creative! Experiment! 
Experimenting is an integral part of the process of mastering a tool in general! (Where do you think I've got all this knowledge of how to use the Affinity apps, huh? )

5 hours ago, Edward_Goodwin said:

It's just annoying that when converting from one node to another actually changes the base shape; I don't see why.

One word: math
Vectors is all just math.

[lacerto]

On 2/24/2023 at 4:10 PM, Edward_Goodwin said:

But really, beyond what I'm trying to achieve here specifically, it's really the principle of the thing I'm after - i.e. how can I transform the sharp node (indicated in the second image) such that I can adjust the curves without a discontinuity? As you can see, I can't simply convert to smooth or smart (I want to retain the geometry of the top circular section)

I agree that keeping the slope whenever possible is what I, too, expect (much based on years of experience working with other similar apps). So when exporting the kinds of shapes you have in your example as an EPS file (or copying them via Clipboard) and editing them in apps like CorelDRAW, Xara Designer or Inkscape), the nodes that are "smooth" in Affinity apps become ones that CorelDRAW and Xara call "cusp" and Inkscape "corner" nodes, meaning that they have handles that are not forced to be moved synched, aligned on a single line but can shape the slope of the curve differently from either side of the node (anchor point). In CorelDRAW, Xara and Inkscape converting such a node to smooth one keeps the shape of the curve unchanged (or at least the conversion routine tries to do so). In CorelDRAW and Xara turning a smooth (in Corel also symmetric) node to cusp will try to keep the shape, as well, while Inkscape makes such nodes ones that Affinity apps call sharp (a corner node without handles), unless they are first converted to smooth ones, after which converting to corner nodes tries to keep the shape (similarly as in CorelDRAW and Xara). Illustrator does basically the same as these other apps though the smooth nodes from Affinity apps behave like smooth nodes also in Illustrator (there shaping the curves as if a node were a "cusp" one, making handles independent, requires using the "Convert Anchor Point Tool", but like in CorelDRAW, Xara and Inkscape, converting a deliberately made cusp anchor point to a corner point, or smooth one, tries to retain the slope of the curve):

I am not sure what the "Smart" node of Affinity apps actually does, it is described in Help as one that "creates a continuous curve but uses a line of best fit". I do not think that other apps have a comparable node. Personally I prefer the node types and conversions of the mentioned other apps. Trying to keep the shape at node conversion whenever possible makes shaping so much easier. In a way I think that the mentioned other apps specifically use "math" in trying to keep the shape of the curve, that is, try to make a perfect conversion.

[Old Bruce]

22 hours ago, Edward_Goodwin said:

Thank you again. If you do think of a way to do what I'm asking, then do drop me a line 🙂 in the meantime, have a good weekend one and all!

I think what happened was you Joined the curve's end nodes instead of Closing the curve.

Using the Node tool drag select the problem node. The square red one. Break the curve there. Drag select the now two coincident nodes there and close the curve.

[Edward_Goodwin]

Thanks Lacerto - it's interesting to see how other apps make the conversion. My experience of Illustrator (admittedly rather an old version) is that no change in line occurs. But I could be misremembering... I don't believe in the 3D CAD packages I use that any conversion from, say, straight lines to splines would result in a change as seen in AD. So I think the 'math' Loukash refers to an be applied in different ways.

 

Old Bruce - thanks for your suggestion. However, I've tried what you've suggested (i.e. breaking the curve and then closing it) and I still get a sharp corner so when I then want to move the node handles to modify the straight line of the 'V', it doesn't move as if it were a constant curve. If I thine alter the node to be smooth/smart, the same changes noted previously occur. Is there some setting on the 'close' function that I'm missing?

 

Edward

[loukash]

37 minutes ago, Edward_Goodwin said:

My experience of Illustrator (admittedly rather an old version) is that no change in line occurs. But I could be misremembering...

I just checked with exactly the same curve, and Illustrator (CS5 here) is smarter than Affinity, albeit not "perfect" either. Like in Affinity though, you can snap the node handle to the curve. (But unlike Affinity, working with Illustrator always is a literal pain in the you-know-where for me. )
So in the end it doesn't make that much difference. Just make use of all necessary snapping option.

Another method to avoid sharp join nodes literally from the start: Make sure your first node is a smooth node. I.e. think ahead while placing the nodes.

[loukash]

6 minutes ago, loukash said:

avoid sharp join nodes literally from the start

Something like this, roughly: