Set Meshing Options with Python?

mariopa · October 30, 2020, 1:15pm

Hello,

I am new to Netget/NGSolve.

I hope you guys can help me, here the manual way I do:

I load a new Geometry into NGSolve.
After that I navigate into “Meshing options…” select “Mash granularity=very coarse” after that under “Mesh Size/Elements per curv…radius” I switch it to the value 5.

After that “Export Mesh” to a *.STL file.

that works fine, but I need to do this automaticly.

I allready wrote a little phyton file:

from netgen.NgOCC import *
from ngsolve import *

geo = LoadOCCGeometry(‘Part.stp’)
mesh = geo.GenerateMesh()
Draw(Mesh(mesh))

mesh.Export(‘Part2.stl’,‘STL Format’)

But I do not have any idea how I can set the “meshing options” first?

Anyone can help?

thanks much,
regards, mario

mariopa · November 3, 2020, 11:13am

no one any idea?

matthiash · November 3, 2020, 12:51pm

Hi Mario,

There are arguments you can pass to the GenerateMesh() function to control the meshing algorithms. For your case, try the following code

from netgen.meshing import MeshingParameters, meshsize
...
mesh = geo.GenerateMesh(meshsize.very_coarse, curvaturesafety=5)
Draw(Mesh(mesh))

Best,
Matthias

mariopa · November 3, 2020, 1:20pm

thx much for your answer, but it does not generate a mesh:

from netgen.NgOCC import *
geo = LoadOCCGeometry(‘Part.stp’)

from netgen.meshing import MeshingParameters, meshsize
mesh = geo.GenerateMesh(meshsize.very_coarse, curvaturesafety=5)
Draw(Mesh(mesh))

it just shows me the Part.stp in the GUI, but not the generated mesh.

what wrong with this?

regards, mario

mariopa · November 3, 2020, 1:55pm

This comes from the console:

NETGEN-6.2-dev
Developed by Joachim Schoeberl at
2010-xxxx Vienna University of Technology
2006-2010 RWTH Aachen University
1996-2006 Johannes Kepler University Linz
Including OpenCascade geometry kernel
optfile ./ng.opt does not exist - using default values
togl-version : 2
OCC module loaded
loading ngsolve library
NGSolve-6.2.1905
Using Lapack
Including sparse direct solver Pardiso
Including sparse direct solver UMFPACK
Running parallel using 6 thread(s)
importing NGSolve-6.2.1905
(should) load python file ‘Skript.py’
load OCC geometry Number of colours in STEP File: 1
Colour [1] = STEELBLUE3 : (0.380392,0.576471,0.752941)
Highest entry in topology hierarchy:
1 solid(s)
Traceback (most recent call last):
File “”, line 4, in
ImportError: cannot import name ‘meshsize’ from ‘netgen.meshing’ (C:\Program Files\ngsolve-v6.2.1905\lib\site-packages\netgen\meshing.py)
Finished executing Skript.py
Preparing visualization (deflection = 0.01) … done

matthiash · November 3, 2020, 2:46pm

Seems your version of NGSolve is outdated (19.05), I suggest you download a recent version. Note that you might also need to update Python to 3.7.

Best,
Matthias

mariopa · November 3, 2020, 4:13pm

Thx, update to recent version worked!

One more question, i wanna set other Meshing Options like:

“max mesh size”
“min mesh size”
“mesh size grading”

is there a help file or something, where i can find the correct commands for python?

at the moment i know:

mesh = geo.GenerateMesh(meshsize.very_fine, curvaturesafety=5)

but how i can set “min mesh size” for examble?
how you guys find out the correct paramaters?

thx much!

regards, mario

matthiash · November 3, 2020, 6:25pm

Hi Mario,

As far as I know, Netgen has no minh setting. Most options are explained by using the python help() function:

from netgen.meshing import MeshingParamters
help(MeshingParameters)

For a comprehensive list of all options you need too look at the source code:

github.com

NGSolve/netgen/blob/master/libsrc/meshing/meshtype.hpp#L1221


      
          public:
            EdgeDescriptor ()
              : tlosurf(-1)
            { surfnr[0] = surfnr[1] = -1; }
          
          
  int SurfNr (int i) const { return surfnr[i]; }
            void SetSurfNr (int i, int nr) { surfnr[i] = nr; }
          
          
  int TLOSurface() const { return tlosurf; }
            void SetTLOSurface (int nr) { tlosurf = nr; }
          };
          
          

          

          
class DLL_HEADER MeshingParameters
          {
          public:
            /**
               3d optimization strategy:
               // m .. move nodes
               // M .. move nodes, cheap functional

The different meshsize variants are defined here:

github.com

NGSolve/netgen/blob/master/python/meshing.py

from .libngpy._meshing import *

class _MeshsizeObject:
    @property
    def very_coarse(self):
        return MeshingParameters(curvaturesafety=1,
                                 segmentsperedge=0.3,
                                 grading=0.7,
                                 chartdistfac=0.8,
                                 linelengthfac=0.2,
                                 closeedgefac=0.5,
                                 minedgelen=0.002,
                                 surfmeshcurvfac=1.,
                                 optsteps3d=5)
    @property
    def coarse(self):
        return MeshingParameters(curvaturesafety=1.5,
                                 segmentsperedge=0.5,
                                 grading=0.5,
                                 chartdistfac=1,

This file has been truncated. show original

Best,
Matthias

mariopa · November 3, 2020, 6:58pm

thx

mariopa · November 5, 2020, 6:44pm

One more question, I am not able to solve:

Under “Meshing Options/General” I can select

First Step
Last Step
Print Messages

and all points under “Additional meshing options”

I allready search for it, is there a way to set those options in python too?

You helped me allready very much but hopefully you can help me again.

thank much!

regards, mario

mariopa · November 10, 2020, 8:28pm

anyone an idea?

i am not able to find a solution

mariopa · November 14, 2020, 6:27pm

i tried to study the source code, but did not found a solution.

help(MeshingParameters) does not show me a solution, so this means I am not able to set these meshing options with a python script?

Is there any other solution to use the meshing options without interacting with the GUI:

First Step
Last Step
Print Messages

it does not matter if python or not, maybe start netgen.exe with a specific command line?

I am coding a tool for ngsolve, wich is meshing much files at the same time automaticaly every file with a differnt meshing option and the users told me they need to set the meshing options listet above.

if there is no solution they have to interact with the GUI, but this is not a good way i need to do this automaticaly in the background.

christopher · November 14, 2020, 10:09pm

first step = perfstepsstart
last step = perfstepsend
in python
and you can set the message level with
ngsolve.ngsglobals.msg_level = 0

Best
Christopher

mariopa · November 14, 2020, 10:25pm

thx very much!

i will try as soon as possible…

mariopa · December 11, 2020, 10:28am

Hello,

I just tried the following python script:

from netgen.occ import *
geo = OCCGeometry(“//STI01/STIWA/mail/ParM/ng/projects/parm/abc/Schuettblech.stp”)
mesh = geo.GenerateMesh(meshsize.very_coarse, perfstepsstart=MESHCONST_ANALYSE, perfstepsend=MESHCONST_OPTSURFACE, curvaturesafety=5)
Draw(Mesh(mesh))
mesh.Export(“//…stl”, ‘STL Format’)

does not work → ‘MESHCONST_ANALYSE’ is not defined

what I did wrong?

(should) load python file ‘\STI01\STIWA\mail\ParM\ng\projects\parm\abc\tmp.py’
Traceback (most recent call last):
File “”, line 2, in
FileNotFoundError: [WinError 3] Das System kann den angegebenen Pfad nicht finden: ‘C:\STI01\STIWA\mail\ParM\ng\projects’
Number of colours in STEP File: 1
Colour [1] = LIGHTBLUE3 : (0.654902,0.760784,0.788235)
Highest entry in topology hierarchy:
1 solid(s)
Traceback (most recent call last):
File “”, line 3, in
NameError: name ‘MESHCONST_ANALYSE’ is not defined
Finished executing \…py
Preparing visualization (deflection = 0.01) … done

cwinters · December 11, 2020, 10:55am

Hi,

having a look at the code, I found a python enum “MeshingStep”:

  py::enum_<MESHING_STEP>(m,"MeshingStep")
    .value("ANALYSE", MESHCONST_ANALYSE)
    .value("MESHEDGES", MESHCONST_MESHEDGES)
    .value("MESHSURFACE", MESHCONST_OPTSURFACE)
    .value("MESHVOLUME", MESHCONST_OPTVOLUME)
    ;

So just use

from netgen.meshing import MeshingStep

mesh = geo.GenerateMesh(meshsize.very_coarse, perfstepsstart=MeshingStep.ANALYSE, perfstepsend=MeshingStep.MESHSURFACE, curvaturesafety=5)

to generate the mesh.

Best,
Christoph

mariopa · December 11, 2020, 12:10pm

thanks very much!

and is there a enum for MESHCONST_OPTSURFACE and MESHCONST_OPTVOLUME too?

regards, mario

cwinters · December 11, 2020, 1:28pm

The enum “MeshingStep” contains all these options (ANALYSE, MESHEDGES, MESHSURFACE, MESHVOLUME). I copied the export to python in my last post.

mariopa · December 11, 2020, 5:06pm

Omg i read it to fast, thx man!

mariopa · December 12, 2020, 2:58pm

.