Knife Project - bridge edge loop with complex mesh?

New to blender. Using 2.90. I have a mesh created from Photogrammetry, it’s a scan of an irregular shaped boulder (stone). I’m trying to cut through the mesh using the knife project tool and bridge the edges, so the cut path remains ‘solid’. All the tutorials I’ve seen for using the knife project tool suggest selecting the edges, then use the bridge edge loops command. The problem is that there are too many edges to manually select. Is there a way to do this automatically? Or am I going about this wrong?

Thanks for any help.

You need to make sure there aren’t any holes already in the mesh, generally if this is a scanned rock the bottom will be empty, you need to fill that before you attempt a boolean type operation.

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The ideal tool for this job is the boolean modifier/operator.

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Select -> Select All By Trait -> Non-Manifold, then deselect what you don’t need.

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With the above and the Fill holes command I was able to close the bottom of my mesh:

I then tried the knife project tool, followed by the Select All By Trait -> Non-Manifold, followed by bridge edge loop. But the result wasn’t good. So instead I did a boolean operator and that seems to have worked well. Need to figure out how to clean up the texture rendering, but in solid mode it looks OK.

Thanks! FWIW this will allow me to 3D scan real boulders to see what my designs will look like before I cut them. Previously I did my design in 2D, I could visualize in my head what it would look like but other people never really understand. Now I will be able to show a model before cutting the stone.

(sorry had to combine all images as one as I am not yet allowed to post multiple, and no I will not actually be cutting the Apple logo, I just grabbed the SVG file for a quick test)