[Gmsh] Use of OpenCASCADE with an STL file?

[Gavin Ridley]

Hello all,

I'd like to define a volume using an OpenCASCADE Box entity, then subtract
a volume defined by an STL from it.

I have attempted to Merge my .stl file into the geometry with the
OpenCASCADE kernel already loaded, then attempt the same operation as
above. This is the behavior I expect to work, for instance, attempting:

SetFactory("OpenCASCADE");
> Merge "dingding.stl";
>
CreateGeometry;
>
Surface Loop(1) = {1};
> Volume(1) = {1};
>
// And some more stuff...
>

Unexpectedly ends up giving:

Error   : Unknown OpenCASCADE surface with tag 1
> Error   : 'dingding.geo', line 3 : Could not add surface loop
> Error   : Unknown OpenCASCADE surface loop with tag 1
> Error   : 'dingding.geo', line 4 : Could not add volume
>

And without OpenCASCADE, the volume gets created successfully.

Is it the case that OpenCASCADE and merged .stl files are incompatible at
the moment in gmsh? Ideally I'd like to generate a CFD mesh for an
obstruction ( from.stl file) in a channel (from OpenCASCADE geometry),
generating a boundary layer mesh as well around the STL file.

-- 
Thanks,
Gavin Ridley
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