Mixing
Selection of Face of a STL by Face Normal value Threshold
-2
I want to write a script in Python which can generate facegroups in a STL as per the Face Normal value condition. For example, Provided is the snap of Stl, Different colour signifies the face group containing the triangular faces satisfying my given face normal threshold. Is there any simple way to do this in python?
Face Group STL
python mesh meshlab numpy-stl
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
add a comment |
-2
I want to write a script in Python which can generate facegroups in a STL as per the Face Normal value condition. For example, Provided is the snap of Stl, Different colour signifies the face group containing the triangular faces satisfying my given face normal threshold. Is there any simple way to do this in python?
Face Group STL
python mesh meshlab numpy-stl
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
What exactly are you wanting to do? Change the 2-byte attribute of the .stl file to some value dependent on the facet normal?
– A.Comer
Jan 2 at 16:29
Yes @A.Comer. I want to group triangles depending on curvature criteria
– Swagatam Sengupta
Jan 3 at 4:28
add a comment |
-2
-2
-2
I want to write a script in Python which can generate facegroups in a STL as per the Face Normal value condition. For example, Provided is the snap of Stl, Different colour signifies the face group containing the triangular faces satisfying my given face normal threshold. Is there any simple way to do this in python?
Face Group STL
python mesh meshlab numpy-stl
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
I want to write a script in Python which can generate facegroups in a STL as per the Face Normal value condition. For example, Provided is the snap of Stl, Different colour signifies the face group containing the triangular faces satisfying my given face normal threshold. Is there any simple way to do this in python?
Face Group STL
python mesh meshlab numpy-stl
python mesh meshlab numpy-stl
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
edited Jan 9 at 12:12
Ilio Catallo
2,1171637
2,1171637
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
asked Jan 2 at 12:07
Swagatam SenguptaSwagatam Sengupta
86
86
What exactly are you wanting to do? Change the 2-byte attribute of the .stl file to some value dependent on the facet normal?
– A.Comer
Jan 2 at 16:29
Yes @A.Comer. I want to group triangles depending on curvature criteria
– Swagatam Sengupta
Jan 3 at 4:28
add a comment |
What exactly are you wanting to do? Change the 2-byte attribute of the .stl file to some value dependent on the facet normal?
– A.Comer
Jan 2 at 16:29
Yes @A.Comer. I want to group triangles depending on curvature criteria
– Swagatam Sengupta
Jan 3 at 4:28
What exactly are you wanting to do? Change the 2-byte attribute of the .stl file to some value dependent on the facet normal?
– A.Comer
Jan 2 at 16:29
What exactly are you wanting to do? Change the 2-byte attribute of the .stl file to some value dependent on the facet normal?
– A.Comer
Jan 2 at 16:29
Yes @A.Comer. I want to group triangles depending on curvature criteria
– Swagatam Sengupta
Jan 3 at 4:28
Yes @A.Comer. I want to group triangles depending on curvature criteria
– Swagatam Sengupta
Jan 3 at 4:28
add a comment |
1 Answer
1
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oldest
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0
I'm sure there's a python library to load stl files, but I've always just written my own, since the file format is pretty simple (see the Wikipedia article for file format description).
Here is my code to read the stl file:
import numpy as np
import struct
def Unique(inputList):
"""
Given an M x N list, this function gets the unique rows by treating all
M Ntuples as single objects. This function also returns the indexing
to convert the unique returned list back to the original non-unique list.
"""
hashTable=dict()
indexList=
uniqueList=
indx=0
for ntuple in inputList:
if not ntuple in hashTable:
hashTable[ntuple]=indx
indexList.append(indx)
uniqueList.append(ntuple)
indx+=1
else:
indexList.append(hashTable.get(ntuple))
return uniqueList, indexList
def IsBinarySTL(filename):
try:
with open(filename,'r') as f:
test=f.readline()
except UnicodeDecodeError:
return True
if len(test) < 5:
return True
elif test[0:5].lower() == 'solid':
return False # ASCII STL
else:
return True
def ReadSTL(filename):
""" Returns numpy arrays for vertices and facet indexing """
def GetListFromASCII(filename):
""" Returns vertex listing from ASCII STL file """
outputList=
with open(filename,'r') as f:
lines=[line.split() for line in f.readlines()]
for line in lines:
if line[0] == 'vertex':
outputList.append(tuple([float(x) for x in line[1:]]))
return outputList
def GetListFromBinary(filename):
""" Returns vertex listing from binary STL file """
outputList=
with open(filename,'rb') as f:
f.seek(80) # skip header
nFacets=struct.unpack('I',f.read(4))[0] # number of facets in piece
for i in range(nFacets):
f.seek(12,1) # skip normal
outputList.append(struct.unpack('fff',f.read(12))) # append each vertex triple to list (each facet has 3 vertices)
outputList.append(struct.unpack('fff',f.read(12)))
outputList.append(struct.unpack('fff',f.read(12)))
f.seek(2,1) # skip attribute
return outputList
if IsBinarySTL(filename):
vertexList = GetListFromBinary(filename)
else:
vertexList = GetListFromASCII(filename)
coords, tempindxs = Unique(vertexList)
indxs = list()
templist = list()
for i in range(len(tempindxs)):
if (i > 0 ) and not (i % 3):
indxs.append(templist)
templist = list()
templist.append(tempindxs[i])
indxs.append(templist)
return np.array(coords), np.array(indxs)
And here is code to compute the facet normals (assuming right-hand-rule)
def GetNormals(vertices, facets):
""" Returns normals for each facet of mesh """
u = vertices[facets[:,1],:] - vertices[facets[:,0],:]
v = vertices[facets[:,2],:] - vertices[facets[:,0],:]
normals = np.cross(u,v)
norms = np.sqrt(np.sum(normals*normals, axis=1))
return normals/norms[:, np.newaxis]
Finally, code to write out the stl file (assuming a list of attributes for each facet):
def WriteSTL(filename, vertices, facets, attributes, header):
"""
Writes vertices and facets to an stl file. Notes:
1.) header can not be longer than 80 characters
2.) length of attributes must be equal to length of facets
3.) attributes must be integers
"""
nspaces = 80 - len(header)
header += nspaces*''
nFacets = np.shape(facets)[0]
stl = vertices[facets,:].tolist()
with open(filename,'wb') as f: # binary
f.write(struct.pack('80s', header.encode('utf-8'))) # header
f.write(struct.pack('I',nFacets)) # number of facets
for i in range(nFacets):
f.write(struct.pack('fff',0,0,0)) # normals set to 0
for j in range(3):
f.write(struct.pack('fff',stl[i][j][0], stl[i][j][1], stl[i][j][2])) # 3 vertices per facet
f.write(struct.pack("H", attributes[i])) # 2-byte attribute
Putting this all together, you can do something like the following:
if __name__ == "__main__":
filename = "bunny.stl"
vertices, facets = ReadSTL(filename) # parse stl file
normals = GetNormals(vertices, facets) # compute normals
# Get some value related to normals
attributes =
for i in range(np.shape(normals)[0]):
attributes.append(int(255*np.sum(normals[i])**2))
# Write new stl file
WriteSTL("output.stl", vertices, facets, attributes, "stlheader")
this code snippet reads an stl file, computes the normals, and then assigns an attribute value based on the squared-sum of each normal (note that the attribute must be an integer).
The input and output of this script look like the following:
answered Jan 3 at 21:07
A.ComerA.Comer
31518
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
0
I'm sure there's a python library to load stl files, but I've always just written my own, since the file format is pretty simple (see the Wikipedia article for file format description).
Here is my code to read the stl file:
import numpy as np
import struct
def Unique(inputList):
"""
Given an M x N list, this function gets the unique rows by treating all
M Ntuples as single objects. This function also returns the indexing
to convert the unique returned list back to the original non-unique list.
"""
hashTable=dict()
indexList=
uniqueList=
indx=0
for ntuple in inputList:
if not ntuple in hashTable:
hashTable[ntuple]=indx
indexList.append(indx)
uniqueList.append(ntuple)
indx+=1
else:
indexList.append(hashTable.get(ntuple))
return uniqueList, indexList
def IsBinarySTL(filename):
try:
with open(filename,'r') as f:
test=f.readline()
except UnicodeDecodeError:
return True
if len(test) < 5:
return True
elif test[0:5].lower() == 'solid':
return False # ASCII STL
else:
return True
def ReadSTL(filename):
""" Returns numpy arrays for vertices and facet indexing """
def GetListFromASCII(filename):
""" Returns vertex listing from ASCII STL file """
outputList=
with open(filename,'r') as f:
lines=[line.split() for line in f.readlines()]
for line in lines:
if line[0] == 'vertex':
outputList.append(tuple([float(x) for x in line[1:]]))
return outputList
def GetListFromBinary(filename):
""" Returns vertex listing from binary STL file """
outputList=
with open(filename,'rb') as f:
f.seek(80) # skip header
nFacets=struct.unpack('I',f.read(4))[0] # number of facets in piece
for i in range(nFacets):
f.seek(12,1) # skip normal
outputList.append(struct.unpack('fff',f.read(12))) # append each vertex triple to list (each facet has 3 vertices)
outputList.append(struct.unpack('fff',f.read(12)))
outputList.append(struct.unpack('fff',f.read(12)))
f.seek(2,1) # skip attribute
return outputList
if IsBinarySTL(filename):
vertexList = GetListFromBinary(filename)
else:
vertexList = GetListFromASCII(filename)
coords, tempindxs = Unique(vertexList)
indxs = list()
templist = list()
for i in range(len(tempindxs)):
if (i > 0 ) and not (i % 3):
indxs.append(templist)
templist = list()
templist.append(tempindxs[i])
indxs.append(templist)
return np.array(coords), np.array(indxs)
And here is code to compute the facet normals (assuming right-hand-rule)
def GetNormals(vertices, facets):
""" Returns normals for each facet of mesh """
u = vertices[facets[:,1],:] - vertices[facets[:,0],:]
v = vertices[facets[:,2],:] - vertices[facets[:,0],:]
normals = np.cross(u,v)
norms = np.sqrt(np.sum(normals*normals, axis=1))
return normals/norms[:, np.newaxis]
Finally, code to write out the stl file (assuming a list of attributes for each facet):
def WriteSTL(filename, vertices, facets, attributes, header):
"""
Writes vertices and facets to an stl file. Notes:
1.) header can not be longer than 80 characters
2.) length of attributes must be equal to length of facets
3.) attributes must be integers
"""
nspaces = 80 - len(header)
header += nspaces*''
nFacets = np.shape(facets)[0]
stl = vertices[facets,:].tolist()
with open(filename,'wb') as f: # binary
f.write(struct.pack('80s', header.encode('utf-8'))) # header
f.write(struct.pack('I',nFacets)) # number of facets
for i in range(nFacets):
f.write(struct.pack('fff',0,0,0)) # normals set to 0
for j in range(3):
f.write(struct.pack('fff',stl[i][j][0], stl[i][j][1], stl[i][j][2])) # 3 vertices per facet
f.write(struct.pack("H", attributes[i])) # 2-byte attribute
Putting this all together, you can do something like the following:
if __name__ == "__main__":
filename = "bunny.stl"
vertices, facets = ReadSTL(filename) # parse stl file
normals = GetNormals(vertices, facets) # compute normals
# Get some value related to normals
attributes =
for i in range(np.shape(normals)[0]):
attributes.append(int(255*np.sum(normals[i])**2))
# Write new stl file
WriteSTL("output.stl", vertices, facets, attributes, "stlheader")
this code snippet reads an stl file, computes the normals, and then assigns an attribute value based on the squared-sum of each normal (note that the attribute must be an integer).
The input and output of this script look like the following:
answered Jan 3 at 21:07
A.ComerA.Comer
31518
add a comment |
0
I'm sure there's a python library to load stl files, but I've always just written my own, since the file format is pretty simple (see the Wikipedia article for file format description).
Here is my code to read the stl file:
import numpy as np
import struct
def Unique(inputList):
"""
Given an M x N list, this function gets the unique rows by treating all
M Ntuples as single objects. This function also returns the indexing
to convert the unique returned list back to the original non-unique list.
"""
hashTable=dict()
indexList=
uniqueList=
indx=0
for ntuple in inputList:
if not ntuple in hashTable:
hashTable[ntuple]=indx
indexList.append(indx)
uniqueList.append(ntuple)
indx+=1
else:
indexList.append(hashTable.get(ntuple))
return uniqueList, indexList
def IsBinarySTL(filename):
try:
with open(filename,'r') as f:
test=f.readline()
except UnicodeDecodeError:
return True
if len(test) < 5:
return True
elif test[0:5].lower() == 'solid':
return False # ASCII STL
else:
return True
def ReadSTL(filename):
""" Returns numpy arrays for vertices and facet indexing """
def GetListFromASCII(filename):
""" Returns vertex listing from ASCII STL file """
outputList=
with open(filename,'r') as f:
lines=[line.split() for line in f.readlines()]
for line in lines:
if line[0] == 'vertex':
outputList.append(tuple([float(x) for x in line[1:]]))
return outputList
def GetListFromBinary(filename):
""" Returns vertex listing from binary STL file """
outputList=
with open(filename,'rb') as f:
f.seek(80) # skip header
nFacets=struct.unpack('I',f.read(4))[0] # number of facets in piece
for i in range(nFacets):
f.seek(12,1) # skip normal
outputList.append(struct.unpack('fff',f.read(12))) # append each vertex triple to list (each facet has 3 vertices)
outputList.append(struct.unpack('fff',f.read(12)))
outputList.append(struct.unpack('fff',f.read(12)))
f.seek(2,1) # skip attribute
return outputList
if IsBinarySTL(filename):
vertexList = GetListFromBinary(filename)
else:
vertexList = GetListFromASCII(filename)
coords, tempindxs = Unique(vertexList)
indxs = list()
templist = list()
for i in range(len(tempindxs)):
if (i > 0 ) and not (i % 3):
indxs.append(templist)
templist = list()
templist.append(tempindxs[i])
indxs.append(templist)
return np.array(coords), np.array(indxs)
And here is code to compute the facet normals (assuming right-hand-rule)
def GetNormals(vertices, facets):
""" Returns normals for each facet of mesh """
u = vertices[facets[:,1],:] - vertices[facets[:,0],:]
v = vertices[facets[:,2],:] - vertices[facets[:,0],:]
normals = np.cross(u,v)
norms = np.sqrt(np.sum(normals*normals, axis=1))
return normals/norms[:, np.newaxis]
Finally, code to write out the stl file (assuming a list of attributes for each facet):
def WriteSTL(filename, vertices, facets, attributes, header):
"""
Writes vertices and facets to an stl file. Notes:
1.) header can not be longer than 80 characters
2.) length of attributes must be equal to length of facets
3.) attributes must be integers
"""
nspaces = 80 - len(header)
header += nspaces*''
nFacets = np.shape(facets)[0]
stl = vertices[facets,:].tolist()
with open(filename,'wb') as f: # binary
f.write(struct.pack('80s', header.encode('utf-8'))) # header
f.write(struct.pack('I',nFacets)) # number of facets
for i in range(nFacets):
f.write(struct.pack('fff',0,0,0)) # normals set to 0
for j in range(3):
f.write(struct.pack('fff',stl[i][j][0], stl[i][j][1], stl[i][j][2])) # 3 vertices per facet
f.write(struct.pack("H", attributes[i])) # 2-byte attribute
Putting this all together, you can do something like the following:
if __name__ == "__main__":
filename = "bunny.stl"
vertices, facets = ReadSTL(filename) # parse stl file
normals = GetNormals(vertices, facets) # compute normals
# Get some value related to normals
attributes =
for i in range(np.shape(normals)[0]):
attributes.append(int(255*np.sum(normals[i])**2))
# Write new stl file
WriteSTL("output.stl", vertices, facets, attributes, "stlheader")
this code snippet reads an stl file, computes the normals, and then assigns an attribute value based on the squared-sum of each normal (note that the attribute must be an integer).
The input and output of this script look like the following:
answered Jan 3 at 21:07
A.ComerA.Comer
31518
add a comment |
0
0
0
I'm sure there's a python library to load stl files, but I've always just written my own, since the file format is pretty simple (see the Wikipedia article for file format description).
Here is my code to read the stl file:
import numpy as np
import struct
def Unique(inputList):
"""
Given an M x N list, this function gets the unique rows by treating all
M Ntuples as single objects. This function also returns the indexing
to convert the unique returned list back to the original non-unique list.
"""
hashTable=dict()
indexList=
uniqueList=
indx=0
for ntuple in inputList:
if not ntuple in hashTable:
hashTable[ntuple]=indx
indexList.append(indx)
uniqueList.append(ntuple)
indx+=1
else:
indexList.append(hashTable.get(ntuple))
return uniqueList, indexList
def IsBinarySTL(filename):
try:
with open(filename,'r') as f:
test=f.readline()
except UnicodeDecodeError:
return True
if len(test) < 5:
return True
elif test[0:5].lower() == 'solid':
return False # ASCII STL
else:
return True
def ReadSTL(filename):
""" Returns numpy arrays for vertices and facet indexing """
def GetListFromASCII(filename):
""" Returns vertex listing from ASCII STL file """
outputList=
with open(filename,'r') as f:
lines=[line.split() for line in f.readlines()]
for line in lines:
if line[0] == 'vertex':
outputList.append(tuple([float(x) for x in line[1:]]))
return outputList
def GetListFromBinary(filename):
""" Returns vertex listing from binary STL file """
outputList=
with open(filename,'rb') as f:
f.seek(80) # skip header
nFacets=struct.unpack('I',f.read(4))[0] # number of facets in piece
for i in range(nFacets):
f.seek(12,1) # skip normal
outputList.append(struct.unpack('fff',f.read(12))) # append each vertex triple to list (each facet has 3 vertices)
outputList.append(struct.unpack('fff',f.read(12)))
outputList.append(struct.unpack('fff',f.read(12)))
f.seek(2,1) # skip attribute
return outputList
if IsBinarySTL(filename):
vertexList = GetListFromBinary(filename)
else:
vertexList = GetListFromASCII(filename)
coords, tempindxs = Unique(vertexList)
indxs = list()
templist = list()
for i in range(len(tempindxs)):
if (i > 0 ) and not (i % 3):
indxs.append(templist)
templist = list()
templist.append(tempindxs[i])
indxs.append(templist)
return np.array(coords), np.array(indxs)
And here is code to compute the facet normals (assuming right-hand-rule)
def GetNormals(vertices, facets):
""" Returns normals for each facet of mesh """
u = vertices[facets[:,1],:] - vertices[facets[:,0],:]
v = vertices[facets[:,2],:] - vertices[facets[:,0],:]
normals = np.cross(u,v)
norms = np.sqrt(np.sum(normals*normals, axis=1))
return normals/norms[:, np.newaxis]
Finally, code to write out the stl file (assuming a list of attributes for each facet):
def WriteSTL(filename, vertices, facets, attributes, header):
"""
Writes vertices and facets to an stl file. Notes:
1.) header can not be longer than 80 characters
2.) length of attributes must be equal to length of facets
3.) attributes must be integers
"""
nspaces = 80 - len(header)
header += nspaces*''
nFacets = np.shape(facets)[0]
stl = vertices[facets,:].tolist()
with open(filename,'wb') as f: # binary
f.write(struct.pack('80s', header.encode('utf-8'))) # header
f.write(struct.pack('I',nFacets)) # number of facets
for i in range(nFacets):
f.write(struct.pack('fff',0,0,0)) # normals set to 0
for j in range(3):
f.write(struct.pack('fff',stl[i][j][0], stl[i][j][1], stl[i][j][2])) # 3 vertices per facet
f.write(struct.pack("H", attributes[i])) # 2-byte attribute
Putting this all together, you can do something like the following:
if __name__ == "__main__":
filename = "bunny.stl"
vertices, facets = ReadSTL(filename) # parse stl file
normals = GetNormals(vertices, facets) # compute normals
# Get some value related to normals
attributes =
for i in range(np.shape(normals)[0]):
attributes.append(int(255*np.sum(normals[i])**2))
# Write new stl file
WriteSTL("output.stl", vertices, facets, attributes, "stlheader")
this code snippet reads an stl file, computes the normals, and then assigns an attribute value based on the squared-sum of each normal (note that the attribute must be an integer).
The input and output of this script look like the following:
answered Jan 3 at 21:07
A.ComerA.Comer
31518
I'm sure there's a python library to load stl files, but I've always just written my own, since the file format is pretty simple (see the Wikipedia article for file format description).
Here is my code to read the stl file:
import numpy as np
import struct
def Unique(inputList):
"""
Given an M x N list, this function gets the unique rows by treating all
M Ntuples as single objects. This function also returns the indexing
to convert the unique returned list back to the original non-unique list.
"""
hashTable=dict()
indexList=
uniqueList=
indx=0
for ntuple in inputList:
if not ntuple in hashTable:
hashTable[ntuple]=indx
indexList.append(indx)
uniqueList.append(ntuple)
indx+=1
else:
indexList.append(hashTable.get(ntuple))
return uniqueList, indexList
def IsBinarySTL(filename):
try:
with open(filename,'r') as f:
test=f.readline()
except UnicodeDecodeError:
return True
if len(test) < 5:
return True
elif test[0:5].lower() == 'solid':
return False # ASCII STL
else:
return True
def ReadSTL(filename):
""" Returns numpy arrays for vertices and facet indexing """
def GetListFromASCII(filename):
""" Returns vertex listing from ASCII STL file """
outputList=
with open(filename,'r') as f:
lines=[line.split() for line in f.readlines()]
for line in lines:
if line[0] == 'vertex':
outputList.append(tuple([float(x) for x in line[1:]]))
return outputList
def GetListFromBinary(filename):
""" Returns vertex listing from binary STL file """
outputList=
with open(filename,'rb') as f:
f.seek(80) # skip header
nFacets=struct.unpack('I',f.read(4))[0] # number of facets in piece
for i in range(nFacets):
f.seek(12,1) # skip normal
outputList.append(struct.unpack('fff',f.read(12))) # append each vertex triple to list (each facet has 3 vertices)
outputList.append(struct.unpack('fff',f.read(12)))
outputList.append(struct.unpack('fff',f.read(12)))
f.seek(2,1) # skip attribute
return outputList
if IsBinarySTL(filename):
vertexList = GetListFromBinary(filename)
else:
vertexList = GetListFromASCII(filename)
coords, tempindxs = Unique(vertexList)
indxs = list()
templist = list()
for i in range(len(tempindxs)):
if (i > 0 ) and not (i % 3):
indxs.append(templist)
templist = list()
templist.append(tempindxs[i])
indxs.append(templist)
return np.array(coords), np.array(indxs)
And here is code to compute the facet normals (assuming right-hand-rule)
def GetNormals(vertices, facets):
""" Returns normals for each facet of mesh """
u = vertices[facets[:,1],:] - vertices[facets[:,0],:]
v = vertices[facets[:,2],:] - vertices[facets[:,0],:]
normals = np.cross(u,v)
norms = np.sqrt(np.sum(normals*normals, axis=1))
return normals/norms[:, np.newaxis]
Finally, code to write out the stl file (assuming a list of attributes for each facet):
def WriteSTL(filename, vertices, facets, attributes, header):
"""
Writes vertices and facets to an stl file. Notes:
1.) header can not be longer than 80 characters
2.) length of attributes must be equal to length of facets
3.) attributes must be integers
"""
nspaces = 80 - len(header)
header += nspaces*''
nFacets = np.shape(facets)[0]
stl = vertices[facets,:].tolist()
with open(filename,'wb') as f: # binary
f.write(struct.pack('80s', header.encode('utf-8'))) # header
f.write(struct.pack('I',nFacets)) # number of facets
for i in range(nFacets):
f.write(struct.pack('fff',0,0,0)) # normals set to 0
for j in range(3):
f.write(struct.pack('fff',stl[i][j][0], stl[i][j][1], stl[i][j][2])) # 3 vertices per facet
f.write(struct.pack("H", attributes[i])) # 2-byte attribute
Putting this all together, you can do something like the following:
if __name__ == "__main__":
filename = "bunny.stl"
vertices, facets = ReadSTL(filename) # parse stl file
normals = GetNormals(vertices, facets) # compute normals
# Get some value related to normals
attributes =
for i in range(np.shape(normals)[0]):
attributes.append(int(255*np.sum(normals[i])**2))
# Write new stl file
WriteSTL("output.stl", vertices, facets, attributes, "stlheader")
this code snippet reads an stl file, computes the normals, and then assigns an attribute value based on the squared-sum of each normal (note that the attribute must be an integer).
The input and output of this script look like the following:
answered Jan 3 at 21:07
A.ComerA.Comer
31518
edited Jan 7 at 15:03
answered Jan 3 at 21:07
A.ComerA.Comer
31518
answered Jan 3 at 21:07
A.ComerA.Comer
31518
answered Jan 3 at 21:07
A.ComerA.Comer
31518
31518
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What exactly are you wanting to do? Change the 2-byte attribute of the .stl file to some value dependent on the facet normal?
– A.Comer
Jan 2 at 16:29
Yes @A.Comer. I want to group triangles depending on curvature criteria
– Swagatam Sengupta
Jan 3 at 4:28