I am facing difficulties while attempting to use the boolean difference operation in Blender. I have attached a test_boolean.blend file that contains a bathymetry model and a cube. My goal is to use boolean difference to produce the output where only the bathymetry and the top portion of the cube remain after the operation or in other words I want to make an object whose bottom will be the bathymetry and the sides will come from the cube. To troubleshoot, I have inspected the face normals of the cube. I would greatly appreciate your assistance in identifying what might be causing the issue. Thank you for your valuable help.
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1$\begingroup$ Hello and welcome. While files, images, and external videos or links may be helpful additions they should not be the only way to obtain information about your issue. Don't make understanding your question rely on downloading a file, watching a video or visiting an external site. Use the builtin tools to upload images or gifs, along with thoroughly explaining the problem in written form so it can be indexed and searched for thus helping future visitors with similar issues. $\endgroup$– Duarte Farrajota Ramos ♦Jul 31 at 16:44
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1$\begingroup$ The faces of your T mesh are inverted, you need to recalculate the normals, then the boolean works on the bathymetry object, I'm not sure what you mean by the "top portion of the cube" though $\endgroup$– moonbootsJul 31 at 16:46
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$\begingroup$ moonboots, thank you so much for your reply. I am new in blender. Did you mean the cube stl as the 'T mesh'? I want to create a fluid domain, the bottom of the fluid domain is the channel bathymetry and everything else will side and top walls which will come from the cube. Thanks a lot. $\endgroup$– ZVY545Jul 31 at 16:50
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2$\begingroup$ I'm not a boolean expert, but I see a number of issues here: 1) the hull is very very thin, 2) it's hard to inspect if it's manifold (it should be for boolean to work properly), 3) mesh debugging shows some faces are intersecting, 4) the triangulation is ugly - some triangles are very long relatively to their base, 5) the dimensions are huge: $1420$ meters on x axis, 6) the coordinates are even bigger, maxing at $y = 1087667.5$ meters! So those are the problems to work on… $\endgroup$– Markus von BroadyJul 31 at 16:51
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1$\begingroup$ Technically it represents a hull (with volume), because the faces are doubled (which you can see if you press C key, then select a bunch of geometry on top, and press G key followed by Z key and move it up - the bottom geometry that you didn't select stays in place, giving the "surface" thickness. And it's good that it has thickness, just maybe should have a little bit more of it for boolean to work. The mentioned points 5) and 6) make it worse, because floating point errors grow a lot as you move away from 0. $\endgroup$– Markus von BroadyJul 31 at 17:24
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