Difference Between the ApparentIntersections in Trim Command

I have a question about a command in Rhino software, specifically the ApparentIntersections option in the Trim command.

As far as I understand, when ApparentIntersections is turned on, it allows for objects to be trimmed even if they don’t intersect exactly. However, when I turn it off, I am still able to use objects that don’t intersect in the Trim command.

Am I missing something? Thank you.

Clip of my testing process

ApparentIntersection will only influence trimming curves in 3d / perspective window.
(as fare is I understood)

as long as your in plane view / planar Projection view (top,left,right, …) “apparent” will always be trimmed.

the black curve got trimmed in perspective view, using the red cutter.

I try to avoid apparent-intersections and recommend not to use this imprecise option.

Edit - from the rhino-help


Determines whether or not curves are trimmed in relation to the view. They do not need to intersect in 3-D space. They only need to appear to intersect in the active viewport.
This option does not apply to surfaces.

kind regards -tom

Apparent intersections can be avoided by using Split and then Delete the unwanted part.

That’s an good alternative, but it ditches “untrim” :laughing:

Thank you! I should have tried it in perspective view before I asked!

Incorrect. Untrim works with Split surfaces.

Appreciate it! I think I will use split more often.

a small but nice fine-tuning:

after applying _split, the resulted fragments are selected.
deselect the part(s) you want to keep.
ctrl click (pc) or ctrl select rectangle
cmd click (mac) or cmd select rectangle

then delete the remaining, selected parts

Nice, will do! Thank you!