I use a mesh grabber for small adjustments to clothes, hair, etc. but I don't think it's suitable for something like digging through the surface.
It's quite an old thread, in the end I solved them by cutting off a part of the original ground using a geometry editor, adding primitives and copying textures.
Good to hear you managed to get the desired effect.
Didn't notice the date of the original post, and was going to reply with the below. I'll reply anyway, incase anyone else has
similar issues.
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Depending on the textures used, you could use a transparency map.
Below is a very rough example:
Steps:
1) Select the surface you want the hole to be using the surface selector tool
2) In the Surfaces tab, go to Base > Base Colour > The texture box > Browse (make note of the name of the texture)
3) Copy and paste the texture. Name it something unique and clear like trans_map.jpg
4) Open with your favourite image editor tool
5) Fill white and colour in black where you want the hole to be. Save. Using the UV view (where you change cameras can help to understand where to position the view, but if it's a complex texture, it might be a lot of trail and error. Also, if the mappings overlap, you may need to create a different surface for the area you want the hole). Example:
6) In the Surface tab, go to Geometry > Cutout opacity and select the down arrow and Browse. Select the file you just saved
7) Parts of the surface will now be transparent and appear like a hole
8) You can use the horizontal and vertical adjustments under Geometry to move the hole to the position you like if it's not in a suitable place
This method can be used in particular for flat surfaces. It becomes more difficult if the object is 3D as the hole will need to be on both sides of the surface. Also, a nice benefit is you can remove the hole by selecting None under Cutout opacity.
Note, the images shown definitely need more work, as the sides aren't properly cut out but this was just as a quick example created in 5 mins.