Difference between revisions of "Mesh to Part/it"

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== Da Mesh a Parte e viceversa==
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== Converting Part objects to Meshes ==
=== Convertire oggetti Parte in Mesh ===
 
  
La conversione di oggetti di alto livello come le [[Part Module/it|forme di Parte]] in oggetti semplici come gli [[Mesh Module/it|oggetti Mesh]] è una operazione piuttosto semplice, nella quale tutte le facce di un oggetto Parte vengono triangolate (suddivise in maglie di una rete). Il risultato di tale triangolazione (tassellatura) viene poi utilizzato per costruire un oggetto mesh:
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Converting higher-level objects such as [[Part Module|Part shapes]] into simpler objects such as [[Mesh Module|meshes]] is a pretty simple operation, where all faces of a Part object get triangulated. The result of that triangulation (tessellation) is then used to construct a mesh: (let's assume our document contains one part object)
 
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<syntaxhighlight>
  #supponiamo che il nostro documento contenga un oggetto Parte
+
  #let's assume our document contains one part object
 
  import Mesh
 
  import Mesh
 
  faces = []
 
  faces = []
 
  shape = FreeCAD.ActiveDocument.ActiveObject.Shape
 
  shape = FreeCAD.ActiveDocument.ActiveObject.Shape
  triangles = shape.tessellate(1) # il numero rappresenta la precisione della tassellatura)
+
  triangles = shape.tessellate(1) # the number represents the precision of the tessellation)
 
  for tri in triangles[1]:
 
  for tri in triangles[1]:
 
     face = []
 
     face = []
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  m = Mesh.Mesh(faces)
 
  m = Mesh.Mesh(faces)
 
  Mesh.show(m)
 
  Mesh.show(m)
 
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</syntaxhighlight>
A volte la triangolazione di alcune facce offerta da OpenCascade è abbastanza brutta. Se la faccia ha una forma rettangolare e non contiene buchi o altre curve di taglio è possibile creare una tassellatura da soli:
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Sometimes the triangulation of certain faces offered by OpenCascade is quite ugly. If the face has a rectangular parameter space and doesn't contain any holes or other trimming curves you can also create a mesh on your own:
 
+
<syntaxhighlight>
 
  import Mesh
 
  import Mesh
 
  def makeMeshFromFace(u,v,face):
 
  def makeMeshFromFace(u,v,face):
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  return mesh
 
  return mesh
  
=== Convertire oggetti Mesh in Parte ===
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</syntaxhighlight>
 +
== Converting Meshes to Part objects ==
  
La conversione di oggetti Mesh in oggetti Parte è un'operazione estremamente importante nel lavoro CAD perché molto spesso i dati 3D si ricevono da altri in formato mesh o sono generati da altre applicazioni. I mesh sono molto pratici per rappresentare le geometrie di forma libera e grandi scene visive in quanto sono molto leggeri, ma per lavori CAD si preferiscono generalmente oggetti di livello superiore, che contengono molte più informazioni, come il concetto di solido, o facce composte da curve invece che da triangoli.
+
Converting Meshes to Part objects is an extremely important operation in CAD work, because very often you receive 3D data in mesh format from other people or outputted from other applications. Meshes are very practical to represent free-form geometry and big visual scenes, as it is very lightweight, but for CAD we generally prefer higher-level objects that carry much more information, such as the idea of solid, or faces made of curves instead of triangles.
  
Convertire gli oggetti mesh in oggetti di livello superiore, come sono  gli oggetti gestiti dal [[Part Module/it|Modulo Parte]] di FreeCAD non è un'operazione facile. L'oggetto Mesh può contenere migliaia di triangoli (per esempio quando è generato da uno scanner 3D), e manipolare solidi costituiti dallo stesso numero di facce sarebbe estremamente pesante. Quindi, in genere, si desidera ottimizzare l'oggetto durante la conversione.
+
Converting meshes to those higher-level objects (handled by the [[Part Module]] in FreeCAD) is not an easy operation. Meshes can be made of thousands of triangles (for example when generated by a 3D scanner), and having solids made of the same number of faces would be extremely heavy to manipulate. So you generally want to optimize the object when converting.
 
 
FreeCAD attualmente offre due metodi per convertire Mesh in oggetti Parte. Il primo metodo è una semplice conversione, diretta, senza alcuna ottimizzazione:
 
  
 +
FreeCAD currently offers two methods to convert Meshes to Part objects. The first method is a simple, direct conversion, without any optimization:
 +
<syntaxhighlight>
 
  import Mesh,Part
 
  import Mesh,Part
 
  mesh = Mesh.createTorus()
 
  mesh = Mesh.createTorus()
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  Part.show(solid)
 
  Part.show(solid)
  
Il secondo metodo offre la possibilità di considerare complanari le sfaccettature delle maglie quando l'angolo tra di loro è inferiore a un certo valore. Questo permette di costruire delle forme molto più semplici:
+
</syntaxhighlight>
 
+
The second method offers the possibility to consider mesh facets coplanar when the angle between them is under a certain value. This allows to build much simpler shapes: (let's assume our document contains one Mesh object)
  # supponiamo che il nostro documento contenga un oggetto Mesh
+
<syntaxhighlight>
 +
  # let's assume our document contains one Mesh object
 
  import Mesh,Part,MeshPart
 
  import Mesh,Part,MeshPart
 
  faces = []
 
  faces = []
 
  mesh = App.ActiveDocument.ActiveObject.Mesh
 
  mesh = App.ActiveDocument.ActiveObject.Mesh
  segments = mesh.getPlanes(0.00001) # tolleranza molto piccola
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  segments = mesh.getPlanes(0.00001) # use rather strict tolerance here
 
   
 
   
 
  for i in segments:
 
  for i in segments:
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  #Part.show(solid)
 
  #Part.show(solid)
  
 +
</syntaxhighlight>
 +
{{docnav|Topological data scripting|Scenegraph}}
  
 +
[[Category:Poweruser Documentation]]
 +
[[Category:Python Code]]
  
{{docnav/it|[[Topological data scripting/it|Script di dati topologici]]|[[Scenegraph/it|Grafo della scena]]}}
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{{clear}}
 
+
<languages/>
{{languages/it | {{en|Mesh to Part}} {{cn|Mesh to Part/cn}} {{fr|Mesh to Part/fr}} {{es|Mesh to Part/es}} {{jp|Mesh to Part/jp}} {{ru|Mesh to Part/ru}} {{se|Mesh to Part/se}} }}
 
 
 
[[Category:Poweruser Documentation/it]]
 
[[Category:Python Code/it]]
 

Revision as of 20:42, 30 September 2014

Converting Part objects to Meshes

Converting higher-level objects such as Part shapes into simpler objects such as meshes is a pretty simple operation, where all faces of a Part object get triangulated. The result of that triangulation (tessellation) is then used to construct a mesh: (let's assume our document contains one part object)

 #let's assume our document contains one part object
 import Mesh
 faces = []
 shape = FreeCAD.ActiveDocument.ActiveObject.Shape
 triangles = shape.tessellate(1) # the number represents the precision of the tessellation)
 for tri in triangles[1]:
     face = []
     for i in range(3):
         vindex = tri[i]
         face.append(triangles[0][vindex])
     faces.append(face)
 m = Mesh.Mesh(faces)
 Mesh.show(m)

Sometimes the triangulation of certain faces offered by OpenCascade is quite ugly. If the face has a rectangular parameter space and doesn't contain any holes or other trimming curves you can also create a mesh on your own:

 import Mesh
 def makeMeshFromFace(u,v,face):
 	(a,b,c,d)=face.ParameterRange
 	pts=[]
 	for j in range(v):
 		for i in range(u):
 			s=1.0/(u-1)*(i*b+(u-1-i)*a)
 			t=1.0/(v-1)*(j*d+(v-1-j)*c)
 			pts.append(face.valueAt(s,t))
 
 	mesh=Mesh.Mesh()
 	for j in range(v-1):
 		for i in range(u-1):
 			mesh.addFacet(pts[u*j+i],pts[u*j+i+1],pts[u*(j+1)+i])
 			mesh.addFacet(pts[u*(j+1)+i],pts[u*j+i+1],pts[u*(j+1)+i+1])
 
 	return mesh

Converting Meshes to Part objects

Converting Meshes to Part objects is an extremely important operation in CAD work, because very often you receive 3D data in mesh format from other people or outputted from other applications. Meshes are very practical to represent free-form geometry and big visual scenes, as it is very lightweight, but for CAD we generally prefer higher-level objects that carry much more information, such as the idea of solid, or faces made of curves instead of triangles.

Converting meshes to those higher-level objects (handled by the Part Module in FreeCAD) is not an easy operation. Meshes can be made of thousands of triangles (for example when generated by a 3D scanner), and having solids made of the same number of faces would be extremely heavy to manipulate. So you generally want to optimize the object when converting.

FreeCAD currently offers two methods to convert Meshes to Part objects. The first method is a simple, direct conversion, without any optimization:

 import Mesh,Part
 mesh = Mesh.createTorus()
 shape = Part.Shape()
 shape.makeShapeFromMesh(mesh.Topology,0.05) # the second arg is the tolerance for sewing
 solid = Part.makeSolid(shape)
 Part.show(solid)

The second method offers the possibility to consider mesh facets coplanar when the angle between them is under a certain value. This allows to build much simpler shapes: (let's assume our document contains one Mesh object)

 # let's assume our document contains one Mesh object
 import Mesh,Part,MeshPart
 faces = []
 mesh = App.ActiveDocument.ActiveObject.Mesh
 segments = mesh.getPlanes(0.00001) # use rather strict tolerance here
 
 for i in segments:
   if len(i) > 0:
      # a segment can have inner holes
      wires = MeshPart.wireFromSegment(mesh, i)
      # we assume that the exterior boundary is that one with the biggest bounding box
      if len(wires) > 0:
         ext=None
         max_length=0
         for i in wires:
            if i.BoundBox.DiagonalLength > max_length:
               max_length = i.BoundBox.DiagonalLength
               ext = i
 
         wires.remove(ext)
         # all interior wires mark a hole and must reverse their orientation, otherwise Part.Face fails
         for i in wires:
            i.reverse()
 
         # make sure that the exterior wires comes as first in the lsit
         wires.insert(0, ext)
         faces.append(Part.Face(wires))
 
 shell=Part.Compound(faces)
 Part.show(shell)
 #solid = Part.Solid(Part.Shell(faces))
 #Part.show(solid)
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