center point of circle path

[Ofnuts]

(10-08-2023, 11:43 AM): "Krikor Wrote:

(10-08-2023, 03:56 AM)sallyanne Wrote:

my gimp has guides for the rectangle and elipse select - would that help?

Hi Sally,

You made a great observation, I don't remember ever noticing this form of centralization before. Really simple and without the need for plugins! 

However, in this technique, the demarcation lines signaling the center are ephemeral, fleeting, lasting only as long as the selection is active, and disappearing as soon as another tool is selected.

It is still possible to register the central points by checking, for example, the information in the Pointer window (yellow circle in the attached figures)

Another way is a plugin I have (I don't know the name of this plugin/script), which is found via the menus: Image - Guides - Center of selection, which creates guides whose intersection is the central point of the selection box.

An interesting point to note is that a path that originated from a selection made by the Ellipse Select Tool will possibly (or always, I can't say) create a false center when submitted to the "ofn-path-to-shape and is" plugin. called Shapes > On Strokes > Circle > Crosshair" - As seen in the attached image.

However, for a path originating from the ofn-path-shape plugin, the generated Crosshair (in red) correctly points to the center of this circle.

This is because the first three points of the ellipse are too close to each other to there are round-off errors (try to do the same with a compass and you will have the same problem).

If you do the same by making a stroke with sufficiently spaced anchors placed on the circle then the crosshair is accurate. As the doc says for the sibling Circumcircle function: "For best accuracy, the three points should be as much spread apart as possible.". Of course circles created by OPTS itself are made of 4 anchors so these are by design sufficiently well spaced (and the crosshair's anchors will be the same as the circle. I could improve the script by trying to find the three most distant anchors.