You are right, there was a bug in pymadcad for the .OBJ importation.
This is fixed in the latest source version and will be available in the next release.
However I think what you are looking for is not extrusion but thickening:
This is the result:
thickscan = thicken(
read('scan.obj'),
0.01, # offset between surfaces
method='point', # 'point' if faster and fine for a higly resolved mesh like this, but leave it to default works also
)
NB
The extrusion function only works shifting by an offset vector, and not along the mesh normals, which is usually not good for closed shapes like this:
thick = extrusion(vec3(0.01,0,0), read('scan.obj'))
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