Coarsening

Mesh coarsening can be performed as part of a mesh quality improvement process, or to reduce the resolution/complexity of a mesh for various other purposes. The Contract() function supports coarsening of either tetrahedral or triangular meshes by contracting edges to achieve the desired edge length. For non-triangular or non-tetrahedral meshes, they can be first converted using solid2tets() or surf2tris() (see also Conversion).

See also: Edge Contraction, Contract().

import mymesh
from mymesh import *
import numpy as np

Surface Mesh Coarsening

threshold = 100
bunny_img = mymesh.demo_image('bunny')
voxelsize = (0.337891, 0.337891, 0.5)

bunny_surf = image.SurfaceMesh(bunny_img, voxelsize, threshold, scalefactor=0.5, method='mc33')

# The feature angle option can be used to preserve sharp edges/corners by
# limiting coarsening in those areas, here it's disabled.
bunny_coarse = improvement.Contract(bunny_surf, 8, FeatureAngle=None, verbose=True)

bunny_surf.plot(view='-x-z')
bunny_coarse.plot(view='-x-z')

• 
• 

Identifying element types...Done

Identifying element edges...Done

Identifying boundary nodes...
        Identifying boundary...Done
        Done
        Edge Contraction:RFBOutputContext()

Identifying mesh nodes...Done
        RFBOutputContext()

Identifying mesh nodes...Done

Label-preserving coarsening

Labels can be assigned to different regions of the mesh to preserve the interfaces between the regions during coarsening. This can be useful for preserving interfaces in multi-material meshes for finite element simulations

# Create a spherical mesh
S = implicit.TetMesh(implicit.sphere([0,0,0], 1), [-1,1,-1,1,-1,1], .1)

# Embed a torus in the mesh
S.NodeData['torus'] = implicit.torus([0,0,0],1,.5)(*S.NodeCoords.T)
S1 = S.Contour('torus', 0, threshold_direction=1, mixed_elements=False)
S1.ElemData['labels'] = np.zeros(S1.NElem)
S2 = S.Contour('torus', 0, threshold_direction=-1, mixed_elements=False)
S2.ElemData['labels'] = np.ones(S2.NElem)
S1.merge(S2)

# Coarsen
Sc = improvement.Contract(S1, 0.2, labels='labels', verbose=True)

visualize.Subplot((S1, Sc, S1.Clip(), Sc.Clip()), (2,2), scalars='labels',
                   show_edges=True, titles=['Original', 'Coarsened', '', ''],
                   view='-yz')

Identifying element types...Done

Identifying element edges...Done

Identifying boundary nodes...
        Identifying boundary...
        Identifying surface...Done
        Done
        Done
        Edge Contraction:
Calculating element centroids...Done

Calculating element centroids...Done
RFBOutputContext()

Identifying element edges...Done

Identifying mesh nodes...Done
        RFBOutputContext()

Identifying surface...Done

Identifying element edges...Done

Identifying mesh nodes...Done
        RFBOutputContext()

Identifying surface...Done

Identifying element edges...Done

Identifying mesh nodes...Done
        RFBOutputContext()

Identifying surface...Done

Identifying element edges...Done

Identifying mesh nodes...Done