Mesh to Part/es: Difference between revisions
(Created page with '== Converting Part objects to Meshes == Converting higher-level objects such as Part shapes into simpler objects such as meshes is a pretty simpl…') |
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== Convertir Objetos parte en mallas == |
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La conversión de objetos de alto nivel, tales como [[Part Module|Part shapes]] en objetos más simples como [[Mesh Module|meshes]] es una operación bastante sencilla, en la que todas las caras de un objeto Parte son triangularizadas. El resultado de esa triangulación (mosaico o teselado) se utiliza para construir una malla: |
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#let's assume our document contains one part object |
#let's assume our document contains one part object |
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Mesh.show(m) |
Mesh.show(m) |
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En ocasiones, la triangulación ofrecida por ''OpenCascade'' para algunas caras es bastante fea. Si la cara tiene un espacio de parámetros rectangular y no contiene ningún agujero o curvas de corte también puede crear una malla por su cuenta: |
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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: |
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import Mesh |
import Mesh |
Revision as of 18:49, 3 September 2010
Convertir Objetos parte en mallas
La conversión de objetos de alto nivel, tales como Part shapes en objetos más simples como meshes es una operación bastante sencilla, en la que todas las caras de un objeto Parte son triangularizadas. El resultado de esa triangulación (mosaico o teselado) se utiliza para construir una malla:
#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)
En ocasiones, la triangulación ofrecida por OpenCascade para algunas caras es bastante fea. Si la cara tiene un espacio de parámetros rectangular y no contiene ningún agujero o curvas de corte también puede crear una malla por su cuenta:
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 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)