Hello community,

I am using outset path to add so called seam allowances to a sewing pattern. Basically this works great, however I have some markings on the path that is to be outset, which I also want to transfer to the outset. How can this be done?

A demonstration to make it easier to understand:
This is my original drawing without the outset:


After duplicating path and outsetting the duplicate path:


Now on the original black path, there are some points (highlighted with red rectangles) for which I need a mapping to the outlined path. Is there any way to let Inkscape map these specific points of the black path to the blue path? I don't even care about e.g. manually moving the diamond (in the upper right red rectangle) to the outlined path, but I want its position on the outlined path to be mathematically as exact as possible and don't want to find the mappings by hand (actually most mappings in this case are quite easy).


Thanks for any support!

I probably don't correctly understand the question. Seems like if you just put the outline and all the "markers" in a group, duplicate (Ctrl-D), resize (e.g., with Ctrl-Shift), the result would have all the markers in the exactly proportional spot.

(Resizing doesn't add the same amount of seam to all borders - that's why it won't work for srynoname)

@srynoname: you'd need to draw a line that is perpendicular to the original path segment to determine the correct position of the marker on the outer path segment.

Tbh., I'm not sure how to do that most easily in Inkscape - maybe by using a rectangle that you rotate until it sits on the inner line, and then place the marker on the intersection of the rectangle with the seam's border. Very manual method, but you probably don't have too many markers.

The problem with using a perpendicular line, is that these notches often occur along a curve, where it would only be visually guessing what is perpendicular at any given point along the line.

Another option might be to combine the original outline path, with the paths that make the diamonds. Then when you outset, it outsets them all at once.

You'll see that it does something unexpected with the diamond shape. But that can be fixed with some node editing. (I mean unexpected to me. I"m sure it actually is correct behavior.)

Another idea would be to select the original outline, and all the diamonds, and do Path menu > Union. It will make the diamonds into triangles (triangular "bumps"). But it would be a single path. And when you outset, it will automatically be in the correct position. And as far as I remember from was making my own clothing from patterns years ago, it's just the outer triangle that matters, after you cut out the fabric.

Hhm, well looking again at your examples, I see not all of the places that you indicated are diamonds. Some of the places are just path intersections. Hhmm....I guess you could put little diamonds/triangles there. Or some other kind of shape.

In this case, those are straight lines. And it would be entirely mathematically correct to just make the lines longer, to where they intersect the outset path. Just scale them. But in cases of curved lines like that, I think you'd have to use something like the diamond/triangles, to mark those places.

Fyi, there's an extension for making clothing patterns with Inkscape. I'll find.... Here: https://github.com/kirchner/patterns I haven't personally used it (don't have a sewing machine anymore), so I'm not sure how well it works. But worth taking a look! Let us know if you like it - I'd be interested to hear.

With custom markers you can ensure perpendicularity to a path at any given node but it seems snapping doesn't work with markers.

Oh if you had nodes placed where your markings are, then you already have those nodes constructed geometrically precise on the outset path.
You can use snapping to the desired nodes on them.

Yeah, after you change the path to a marker, it doesn't have nodes anymore. Although with zooming, you could still align the notch triangles pretty darn close (to a marker), manually.

I don't think the offset path keeps the same nodes. Hhm no, it adds extra nodes, and they move around with each additional offset step. Not as much on perfectly straight segments, but on curves.

Edit
By the way, I tried to install that extension, to try and help another member. But apparently it's not working - missing some major files - won't even be installed.

Markers are still vectors, theoretically they could be snappable.
Guess such an option could trigger alot of issues though -by changing stroke width&resizing the markers it could snap back to its original state, preventing adding a different stroke width etc.-.

Anyway, here is a screen capture of the dynamic offsetting preserving the node in question.

Guys, thank you all for your replies. I didn't receive any mail notifications about new replies and just saw your replies when checking manually today.
As brynn suggested I tried Path combine and path union, however both methods share the same (logical) side effect: the diamond (or better triangle after combine/union) becomes larger than in the original:

As short reminder, this is the original (excerpt):


Path combine (diamond combined with sewing pattern), outset:


Path union (diamond unioned with sewing pattern), outset:


Well, unfortunately neither of these results fulfills the requirement of just placing the normally sized diamond (triangle) on the outset for obvious reasons (triangle is part of original path and therefore increased in size during the outset operation to keep an equal distance to the original).

My next solution attempt would be to check if there is any good way to create a tangent through a point on the path of the sewing pattern and intersect this tangent with the outset path. Is anyone aware of any extension for this? Any chance to develop such an extension myself? (coding skills available). I don't want to do this by hand / without math. Thanks

I believe that should be possible. The latest Inkscape version allows you to select nodes and use the node selection in your extension. I'd probably create a perpendicular guide that goes through the node. No idea about the math, but I assume it's already there in some other extension - there is one extension that can draw node handles, I'd start out with that one. For the node selection, I'd look into the demo extension, which you can find attached to https://bugs.launchpad.net/inkscape/+bug/171640 . For how to create a guide, look into the extensions that create guides.

Use dynamic offsetting and markers?

First, dynamic offset the path, convert it to a path,
split its nodes at the right position. That will (re)define the start-end node of the path which you can assign a custom triangle-shaped marker to.
Only necessary converting dynamic offset to a path because somehow a dynamic offsetted path's start-end node is always at the top -where its default handle appears.

Well, even though the outset makes the triangle bigger, the point of triangle is mathematically in the correct position. It's much better than manually trying to place a separate triangle/diamond. So you can draw a straight line from the tip of the large triangle to the tip of the small one. And any point along that line will be the correct position for the point - including where it intersects with the cutting line, if it was continuous, and not interrupted by the triangle. So that intersection is the point where you would want to place a new triangle. The tip of the triangle could even snap right to that line.

However, if this is the seam allowance, does it really matter if the triangle is bigger? I know when most people cut out a pattern, they cut the diamond with the point outward (at least they did back in my day). But back in my Mom's day, a lot of people would cut the diamond inward, making a notch. The whole reason for those points or notches is to be able to correctly align other pattern pieces. Does it really matter if it's bigger than normal?

Now, if you were, for example, making different sizes of patterns for sale or something, you might want normal size diamond/triangles. But for the seam allowance, and if it were for my own clothes, personally I wouldn't worry. I might not even worry if it was for someone else. Who would ever see it? I'd either just cut larger triangles, or I'd cut notches instead.

(Unless you go into your profile and choose to get a notification for every message that you post, you'll need to individually subscribe to topics, when you post them. See that tiny wrench icon, just to the right of the Post Reply button, near the bottom of the page? Just click the first option from the dropdown menu "Subscribe Topic".)

Wouldn't "snap to perpendicular" solve your problem finding the point where to place your diamonds or line intersections on the outset?
You'll find it in Document Properties (Shift+Ctrl+D) | Snap-Tab | Miscellaneous | Snap perpendicularly
You also need to have "snap to paths" enabled.

Yep, theozh, that's a good idea

It's a good idea! But the problem with snap to perpendicular, is the same problem with drawing a square and aligning along the path. It would be very hard to start your path at the correct point (in the center of the 2 sides of the triangle). Drawing the line from the point of the original to the point of the outset determines precisely the point which is at the center of the triangle (after you extend it).

So you could use that little line to start the new path, and then snap it perpendicular to the outer path. However, if you've already drawn the line from point to point, you don't really need a path to snap perpendicular.

Or if you started the path on the tip of the triangle, where it would snap, then snap the other end perpendicular. But it's still going to be the same thing as drawing the path from point to point.

But leaving all that discussion to the side for the moment. If this is the seam allowance, unless you're going to be selling these patterns, I'm not sure if it matters if the triangle is a little larger.

Well, the OP didn't tell whether or how he placed the diamond or triangle "correctly" in a "mathematical sense" on the original path or how he is getting to a specific point.

I would start with a single point on the original curve at the desired position
e.g. via
a) node tool (F2) and double clicking on the curve with "snapping to path" enabled which is generating a point on the curve
b) or with snap to intersection with another reference line and double click

If you have created the original point and that little perpendicular path between the starting point on the original curve and the outset, change the stroke (Shift+Ctrl+F) and look for suitable start and end markers. However, I haven't found suitable diamonds/triangles but I expect that you can create custom ones with proper shape and size.

If you don't want to have a line between original path and outset simply set the stroke to zero. Unexpectedly, the markers will keep their size. Which I would call a bug (or is it a feature?), but in this case it helps .

Left stroke 0.5, right stroke set to 0.0 markers remain.

Thanks again to all your replies!
@brynn: I am already subscribed, no idea what's going wrong here currently. Not so important though.

I skipped experimenting Lazur's dynamic offset suggestion in favor of theozh's perpendicular (I actually mixed up tangent and perpendicular in my last post) which works great for me. After drawing the perpendicular I duplicate my diamond and move it to the other end of the perpendicular where its center snaps as "line midpoint to path intersection" to the end of perpendicular:

I will have to test further, but it seems like this way is working sufficient for me.

BTW indeed I did place the diamonds by hand, so yes, I am not completely "mathematical" correct. I even forgot that myself!
Now it's time to finish my first digital pattern Great community here