[Gmsh] Bounding Box of an imported STL Smaller than geometry?

[Christophe Geuzaine]

Hi Baltasar,

Indeed we sub-sampled discrete entities to compute bounding boxes. I just changed this to a "brutal" bounding box computation in the latest dev snapshot: give it a try (If it's really too slow we should consider storing the information.)

Christophe


> On 23 Jun 2020, at 18:41, Baltasar Rüchardt <baltasar.ruechardt at ds.mpg.de> wrote:
> 
> Dear everyone,
> 
> I hope you are dealing as good as possible with the pandemic.
> 
> I am puzzled because the bounding box that I obtain from a stl geometry
> is smaller than the volume defined by the surface.
> 
> The procedure used is as follows:
> 
> 1. Import stl
> 2. Use Bounding Box on surface
> 3. Create Points by coordinates obtained from Bounding Box
> 4. Connect points to make a volume.
> 
> This is done in create_to_small_box.geo [which should have rather be
> named create_too_small_box.geo ...].
> 
> Background: The stl shows the surface of a heart obtained from a mrt
> scan. I first shrink / expand it using the Plugin(Transform) and then I
> want to translate it (again using the Plugin(Transform).Tz) such that
> the tip of the heart is at the same height as the edge of an electrode
> (small example in show_application_of_transforms.geo). My approach was
> to use the bounding box zmin- value to compare the heights and then
> calculate the necessary transformation by calculating tz= zmin_electrode
> - zmin_heart .
> 
> Does someone have a suggestion? Or any help? The alternative would be to
> move the stl with meshlab such that the heart tip is at heigh zero, then
> I could apply the shrinking and transform in gmsh without problems.
> 
> Thank you very much in advance!
> 
> Best regards
> 
> Baltasar Rüchardt
> 
> 
> Gmshinfo:
> 
> Version       : 4.6.0
> License       : GNU General Public License
> Build OS      : MacOSX
> Build date    : 20200622
> Build host    : gmsh.info
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> FLTK version  : 1.4.0
> PETSc version : 3.9.3 (real arithmtic)
> OCC version   : 7.4.0
> MED version   : 4.0.0
> Packaged by   : geuzaine
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> Issue tracker : https://gitlab.onelab.info/gmsh/gmsh/issues
> <bounding_box_smaller_than_stl.png><create_to_small_box.geo><outer_boundary.stl><show_application_of_transforms.geo>_______________________________________________
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— 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine