Celtic knots in Inkscape part 2: A better way

Go figure! As soon as I slept on it after posting that last tutorial, it occurred to me that there’s a much better way to handle the cutting. For some shapes it may take a bit longer—not a lot—but it involves so much less precision. In this case I think it’s actually a time saver, so it’s a win-win. This concept involves the fact that since we know which final pieces will appear in the knot, we can just cut out the final pieces individually (taking advantage of symmetry of course) or maybe two or three at a time, rather than trying to do a bunch at once.

So heck, let’s try it. Get the previous tutorial up through step 7c.

Step 7d: Before we do anything else, let’s delete the copies of the uncut knot on the page itself, but leave the backup copies that got moved down via Shift+Down. From here on out, I’m calling those backups “templates”. In this version, we’re going to repeatedly make copies of the templates—some to use as stencils, some to use as the knot pieces—and then use Shift+Up a few times to move them into position.

Step 8: I’m going to start by trying to do the north leaf piece. Select the leaf template, and duplicate it with Ctrl+D. Change its color to green, but leave the stroke width at 5 px; this is going to be the new piece we’re cutting, and from here out I’m calling it the subsection. Duplicate it again, but make the duplicate’s color dark red and give it a 7.5 px stroke width; this will be one stencil. Now duplicate the ellipse, make it orange, and again give it a 7.5 px stroke width. So we should have one piece that will be cut, and two stencils.

Step 9a: Time to cut our stencils and our subsection. These are still just strokes at this point. Remember the north leaf subsection should start on the left where it comes out from under the ellipse, so this is where the ellipse will cut it. So first, using the node tool let’s remove the northeast quadrant of the ellipse. That’s the one we know for sure we don’t want. No need to subdivide! I’m keeping the others around on a just-in-case basis, which is about to come in handy later.

Step 9b: The leaf stencil needs to be cut now. We’ll be chopping off quite a lot of it. For starters, snip off the two line segments at the tips of each leaf. Then we’ll cut off everything else, except for the line that runs from the bottom of the east leaf to the left of the north leaf. At this point you should see that the top leaf section is exactly what we’ll want in the final product.

Step 9c: The green subsection itself has lots of extraneous bits we’re not going to need, but before we start snipping, there’s an opportunity here. This is why I kept more of the ellipse stencil. It looks like we can make the interior western cross piece at the exact same time we do the north leaf piece, so let’s kill two birds with one stone. On the subsection, snip off the line segments at the tip of every leaf except the north one. Now remove any bits that aren’t part of the north leaf section or that west interior crossing. Your final result should look like so:

knot-tutorial-13

There’s a little bit of the green subsection outside of where we want it, but no worries; it can be deleted later.

Step 9d: This is where we do the cutting. Select the green subsection and the two stencils, and convert Stroke to Path. Now select the two stencils; in the Path menu, choose Union to make this just one stencil. Then Shift+click to select the green subsection, and do a Difference. Finally, we have two of our knot sections. The third little bit we have to get rid of though, so go into the node tool and select all of the nodes in that tiny little leftover piece, and delete them. Now go back to the Select too, and use Shift+Up a few times to move this piece into position. Change its fill color to black, and these two pieces are done.

knot-tutorial-14

Step 10a: The eastern leaf subsection can be done now, and it seems like the north interior crossing ought to go right along with it. So let’s do that. Repeat step 8 to get our subsection and stencil pieces. Snip off the southeast quadrant of the ellipse.

Step 10b: For the leaf stencil, we want only the line running from the left of the south leaf to the top of the east leaf. Lose everything else. There is a little bit of this stencil overlapping the east leaf outside of the ellipse, which isn’t good, so we’ll have to subdivide just this once. Select the line segment in the far northeast (select both nodes or click the line), hit the icon in the node toolbar that says “Insert new nodes into selected segments”, and then select only the node on the very northeast tip and delete it.

Steb 10c: You know the drill. Lose every piece of the subsection that’s not part of the east leaf, or the north interior crossing. Once again there should be a little piece of the green subsection left over that we’ll get rid of later; this one is the top part of the east leaf that’s just inside the ellipse.

knot-tutorial-15

Step 10d: Just like before, use Stroke to Path on all three pieces. Union the two stencils, Difference the new stencil and the subsection, then get rid of the leftover bit on the subsection in the node editor. Move it up, color it black, and now these two pieces are done. We have two leaves and two of the interior crossings, and can do the rest with symmetry, so the leaf portions are finished. All that’s left is the ellipse!

Step 11a: Repeat step 8 for the last time, except this time we need the ellipse to be the subsection (green), we need a leaf stencil (red), and there will be no other stencil. We’ll get all four sections of the ellipse out of this, no need for symmetry. Cut the leaf stencil to remove the line segments on the left of the north leaf, the top of the east leaf, etc.

knot-tutorial-16

Step 11b: All we do now is select the subsection and stencil, convert Stroke to Path as before, and do a Difference. There’s nothing to delete. Shift+Up to move this into place, make it black, and we’re almost done.

Step 12: The only thing left is to fill in the other pieces via symmetry. This is only needed for the leaf and crossing sections. There should be two paths to select, so select them both and in the Path menu, choose Combine to make them one object. Make sure you’re in the Select too. Click the object again to show the rotation handles and the center of rotation; we’re going to drag that center of rotation to the center of the page.

knot-tutorial-17

As in the previous tutorial, you’ll then duplicate this and either flip twice (once each way) or rotate twice to achieve a 180° rotation.

Step 13: Select all three objects, go to the Path menu, and Combine. The knot is finished. Go ahead and delete the templates now.

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About Lummox JR

Aspiring to be a beloved supervillain
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One Response to Celtic knots in Inkscape part 2: A better way

  1. northampton70@o2.co.uk says:

    great stuff lee – keep up the good work I will try on inkscape to copy – peter

    slainte

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