Hi Marc,

> The "center" snap does not appears to work on the
> planets, most probably the related to the scale...

Yup, that's definitely related to the scale - the thing that detects whether a curve is an arc or not doesn't work on such large scaled objects because it uses a pretty tight tolerance to validate that different points on the curve give the same center point as expected with an arc.

But with objects at such a huge scale, a lot of smaller-sized calculation accuracy is lost (that's just how floating point math on the computer works, it's what allows for a wide range of possible numbers to be stored in a fairly small amount of memory), and that makes the center point calculations different enough for the circle to not register as an arc anymore as far as the center osnap code is concerned.

You'll see all kinds of various side effects from losing calculation precision with large numbers like this.

In some cases I've tuned up the calculations to use a tolerance factor that's some relative fraction of the object's overall bounding size, and things that have been adapted to this system instead of only a fixed size tolerance can work better in these cases. I can probably make center object snap tuned up to work in this way so that it would work on these objects, I've made a note for that to try for v3.

- Michael