How can you create paths with precise curvatures in Inkscape?

Question

I want to curve the line between points of a path using a specific value. Instead of dragging the line to curve it, I want to type a specific curvature value. Otherwise, it is impossible to get two line curved exactly the same way.

The exact coordinates of points in a path can easily be set. However, I really haven't found a way to specify the position of the curvature "direction" (see below).

How can this be done in Inkscape?

Answer 1

There is no numerical input for the curvature in the Inkscape GUI. This isn't something you will typically find in vector software anyway, not just in Inkscape. I mean you could technically edit the path data manually in the XML editor, but that's not exactly user friendly.

I'd suggest a different approach.

Drop a vertical guide, and draw one half of the shield as a closed shape directly against the guide, use snapping to get it exact, then apply a Mirror Symmetry Live Path Effect.

An example

If you need to convert the path effect to an actual shape, do Path > Object to Path, then do Path > Union

Answer 2

You get the left and right sides curved in the same way easily by drawing only one, say the left half of the shape. Make a copy, flip it and combine the halves. Use path joining if the halves are open curves. Combine with path union if you made closed shapes. In both cases you must have node snapping on for perfect placement.

You said you want to give a certain numeric curvature. In rigorous math your declaration means that you want to use circular arc. That's well possible. Inkscape allows drawing arcs. As well you can take a part of a circle.

To make it all easy practice with path operations such as making an union (a.k.a. add), Intersect and subtract. And cut + divide. Soon you'll wonder why this seemed difficult.

An example:

The black pieces are subtracted from the blue shapes. A flipped copy is made. The halves are combined to union and a stroke is inserted to show it's now one piece.