netgen/python/read_gmsh.py

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from netgen.meshing import *
def ReadGmsh(filename):
meshdim = 1
with open(filename + ".msh", 'r') as f:
while f.readline().split()[0] != "$Elements":
pass
nelem = int(f.readline())
for i in range(nelem):
line = f.readline()
eltype = int(line.split()[1])
if eltype > 1 and eltype != 15:
meshdim = 2
if eltype > 3 and eltype != 15:
meshdim = 3
break
f = open(filename + ".msh", 'r')
mesh = Mesh(dim=meshdim)
pointmap = {}
facedescriptormap = {}
namemap = {}
materialmap = {}
bbcmap = {}
while True:
line = f.readline()
if line == "":
break
if line.split()[0] == "$PhysicalNames":
print('WARNING: Physical groups detected - Be sure to define them for every geometrical entity.')
numnames = int(f.readline())
for i in range(numnames):
f.readline
line = f.readline()
namemap[int(line.split()[1])] = line.split()[2][1:-1]
if line.split()[0] == "$Nodes":
num = int(f.readline().split()[0])
for i in range(num):
line = f.readline()
nodenum, x, y, z = line.split()[0:4]
pnum = mesh.Add(MeshPoint(Pnt(float(x), float(y), float(z))))
pointmap[int(nodenum)] = pnum
if line.split()[0] == "$Elements":
num = int(f.readline().split()[0])
for i in range(num):
line = f.readline().split()
elmnum = int(line[0])
elmtype = int(line[1])
numtags = int(line[2])
# the first tag is the physical group nr, the second tag is the group nr of the dim
tags = [int(line[3 + k]) for k in range(numtags)]
if elmtype == 1: # 2-node line
num_nodes = 2
elif elmtype == 2: # 3-node trig
num_nodes = 3
elif elmtype == 3: # 4-node quad
num_nodes = 4
elif elmtype == 4: # 4-node tet
num_nodes = 4
elif elmtype == 5: # 8-node hex
num_nodes = 8
elif elmtype == 6: # 6-node prism
num_nodes = 6
elif elmtype == 7: # 5-node pyramid
num_nodes = 5
elif elmtype == 15: # 1-node point
num_nodes = 1
else:
raise Exception("element type", elmtype, "not implemented")
nodenums = line[3 + numtags:3 + numtags + num_nodes]
nodenums2 = [pointmap[int(nn)] for nn in nodenums]
if elmtype == 1:
if meshdim == 3:
if tags[1] in bbcmap:
index = bbcmap[tags[1]]
else:
index = len(bbcmap) + 1
if len(namemap):
mesh.SetCD2Name(index, namemap[tags[0]])
else:
mesh.SetCD2Name(index, "line" + str(tags[1]))
bbcmap[tags[1]] = index
elif meshdim == 2:
if tags[1] in facedescriptormap.keys():
index = facedescriptormap[tags[1]]
else:
index = len(facedescriptormap) + 1
fd = FaceDescriptor(bc=index)
if len(namemap):
fd.bcname = namemap[tags[0]]
else:
fd.bcname = 'line' + str(tags[1])
mesh.SetBCName(index - 1, fd.bcname)
mesh.Add(fd)
facedescriptormap[tags[1]] = index
else:
if tags[1] in materialmap:
index = materialmap[tags[1]]
else:
index = len(materialmap) + 1
if len(namemap):
mesh.SetMaterial(index, namemap[tags[0]])
else:
mesh.SetMaterial(index, "line" + str(tags[1]))
materialmap[tags[1]] = index
mesh.Add(Element1D(index=index, vertices=nodenums2))
if elmtype in [2, 3]: # 2d elements
if meshdim == 3:
if tags[1] in facedescriptormap.keys():
index = facedescriptormap[tags[1]]
else:
index = len(facedescriptormap) + 1
fd = FaceDescriptor(bc=index)
if len(namemap):
fd.bcname = namemap[tags[0]]
else:
fd.bcname = "surf" + str(tags[1])
mesh.SetBCName(index - 1, fd.bcname)
mesh.Add(fd)
facedescriptormap[tags[1]] = index
else:
if tags[1] in materialmap:
index = materialmap[tags[1]]
else:
index = len(materialmap) + 1
if len(namemap):
mesh.SetMaterial(index, namemap[tags[0]])
else:
mesh.SetMaterial(index, "surf" + str(tags[1]))
materialmap[tags[1]] = index
mesh.Add(Element2D(index, nodenums2))
if elmtype in [4, 5, 6, 7]: # volume elements
if tags[1] in materialmap:
index = materialmap[tags[1]]
else:
index = len(materialmap) + 1
if len(namemap):
mesh.SetMaterial(index, namemap[tags[0]])
else:
mesh.SetMaterial(index, "vol" + str(tags[1]))
materialmap[tags[1]] = index
nodenums2 = [pointmap[int(nn)] for nn in nodenums]
if elmtype == 4:
mesh.Add(Element3D(index, [nodenums2[0], nodenums2[1], nodenums2[3], nodenums2[2]]))
elif elmtype in [5, 6, 7]:
mesh.Add(Element3D(index, nodenums2))
return mesh