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This shows how Knotter can be used to trace a knot from a picture of the knot.

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Sketching the knot

We can now zoom in and use the Edge loop tool. Tutorial picture7.png

We can now start placing the nodes in the canvas with the left mouse button.

It may take some experience to understand where to place them. This process, called "extraction" is described in Celtic Knotwork: the ultimate tutorial - Extraction Tutorial picture8.png

Complete the first part. To exit from the edge chain right click. Tutorial picture9.png

Now the graph corresponds to the image but there is a discrepancy with the rendered knot: the background image has no crossing at the center but the knot does.

This can be fixed changing the type of the edge in the middle which can be achieved with the mouse wheel or right-clicking on the edge. Tutorial picture10.png

Before continuing we can adjust a bit the style.

A wider rope will be easier to see when we zoom out. Tutorial picture11.png

Making the color slightly transparent allows us to see through the knot. Tutorial picture12.png

We proceed and draft the graph on the central part of the cross. Tutorial picture13.png

Follows the right arm of the cross, the left arm is symmetrical. Tutorial picture14.png

And the base of the cross. Tutorial picture15.png

We now proceed the the two knots under the cross. Tutorial picture16.png Tutorial picture17.png

Here is the result, with the color back to fully opaque. The knot follows the image very closely but it's not fully symmetrical. Tutorial picture18.png

Fine-tuning the graph

Here is the result of the previous part, with the background disabled.

We need to make the design more symmetrical, for this we will be using the grid.

Tutorial picture19.png

We start with a 16px square grid and move the center to one of the central nodes.

Click Move... on the grid dialog and then click on the desired node to move the grid.

No we switch from the Edge chain tool to the Edit graph tool.

The nodes will be snapped to the grid when moved or double-clicked. Tutorial picture20.png

After having snapped the four central nodes, we change the grid shape to Triangle 1 to snap the node leading to the top. Tutorial picture21.png

We now change to a 12 pixels square grid centered on the tip of the triangle. Tutorial picture22.png

We snap the nodes on the top arm of the cross. Tutorial picture23.png

Note that the highlighted node does is not making a cusp, the line above is a smooth curve. The underlying image instead has a pointed tip in that location. Tutorial picture24.png

With that node selected we change the minimum angle required to trigger a cusp in the selection style dialog. This will affect only the selected node. Since the angle is 180°, something less than that will suffice. A value too low (below 90° in this case) will trigger extra cusps also for the lines leading down. Tutorial picture25.png

We now move back down and use a 16 pixels Triangle 2 grid to snap the node leading to the right. Tutorial picture26.png

With the same procedure used on the top, we snap the nodes on the right arm of the cross. The same steps are required for the left arm and the base. Tutorial picture27.png

Note that you can snap a bunch of nodes at the same time if they are selected and you use Grid → Snap to grid Tutorial picture28.png

We snap the other two knots. Tutorial picture29.png Tutorial picture30.png

Some of the nodes require the same styling as the one on top of the cross. Make sure that you choose a proper value for the angle. For the bottom-most knot a value of 100° is too low. Tutorial picture31.png

Here is the knot so far. Tutorial picture32.png

We can now change the style and display to make it more appealing.

Here is the knot with the same color as the image and a black outline. Tutorial picture33.png

Now the knot is complete!