STEP file dimensions

tommaso
Topic Author
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New Member

5 years 1 month ago #1966 by tommaso

STEP file dimensions was created by tommaso

Hello,

I'm trying to understand how the imported STEP geometry dimensions are taken into account by Netgen.
To do so I calculate the volume of two geometry objects created one with CSGeometry and the other imported from a STEP file with OCCGeometry.
In principle they are identical. Two prisms with mm size length (where meter=1).

If I run the code:

Code:

import ngsolve as ng
from netgen import csg, occ

prism = csg.OrthoBrick( csg.Pnt(-2e-3,-2e-3,-1e-3), csg.Pnt(2e-3,2e-3,1e-3) )
geo1 = csg.CSGeometry()
geo1.Add(prism)
m1 = geo1.GenerateMesh()
vol1 = ng.Integrate(1, ng.Mesh(m1))

geo2 = occ.OCCGeometry('prism.step')
m2 = geo2.GenerateMesh()
vol2 = ng.Integrate(1, ng.Mesh(m2))

I'm attaching the STEP file I used in the example (I had to change file extension to txt because the forum doesn't allow me to upload step files. You need to change the extension to test the code).
I verify the STEP file dimensions by looking at it's code. See for example the line:

Code:

#23 = CARTESIAN_POINT('',(-2.E-03,-2.E-03,-1.E-03));

and line:

Code:

#166 = ( LENGTH_UNIT() NAMED_UNIT(*) SI_UNIT($,.METRE.) );

As a result:

Code:

vol1
3.200000000000064e-08

as it should be.
While:

Code:

vol2
32.00000000000064

Like if dimensions where in meter.

Why do I get such a difference? How can Ii take into account the right dimensions of a STEP file?

Thanks for your help,

Tommaso

Attachments:

prism_m.txt

christopher
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Administrator

5 years 1 month ago - 5 years 1 month ago #1970 by christopher

Replied by christopher on topic STEP file dimensions

Hi Tommaso,
OCC internally uses mm per default and we do not change that. So step models imported Netgen are always in mm.
Best
Christopher

Last edit: 5 years 1 month ago by christopher.

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