OCC: interface to open-cascade

Preamble

OCC performs CAD operations and surface meshing using open-cascade.

To use the module with the Converter.array interface:

import OCC

To use the module with the CGNS/Python interface:

import OCC.PyTree as OCC

List of functions

– CAD to surface mesh

OCC.PyTree.meshAll

Get a first TRI meshed tree linked to CAD.

– CAD to surface mesh (legacy functions)

OCC.convertCAD2Arrays

Convert a CAD (IGES or STEP) file to arrays.

OCC.PyTree.convertCAD2PyTree

Convert a CAD (IGES or STEP) file to pyTree.

– CAD manipulation

OCC.readCAD

Read CAD file and return a CAD hook.

OCC.writeCAD

Write CAD file.

OCC.getNbEdges

Return the number of edges in CAD hook.

OCC.getNbFaces

Return the number of faces in CAD hook.

OCC.getFaceArea

Return the area of given faces.

OCC._translate

Translate all or given faces.

OCC._rotate

Rotate all or given faces.

OCC._splitFaces

Split all faces to be less than area.

OCC._mergeFaces

Merge some faces.

OCC._sewing

Sew some faces (suppress redundant edges).

Contents

CAD to surface mesh

OCC.PyTree.meshAll(hook, hmin=-1, hmax=-1., hausd=-1.)

Mesh a CAD with triangles. If hmin=hmax, mesh with a regular h. If hmin, hmax and hausd are set, mesh with isotropic triangles with local size adapted to curvature. hausd is the max chordal error of mesh to CAD. This function returns a tree with two bases (EDGES and FACES). EDGES contains discretized edges with a link to the global edge number in CAD. FACES contains discretized faces with a link to the global face number in CAD.

Parameters:

hook (CAD hook) – CAD hook

Return type:

mesh

CAD to surface mesh (legacy functions)

OCC.convertCAD2Arrays(fileName, format='fmt_iges', h=0., chordal_err=0., growth_ratio=0., algo=1)

Read a CAD and return arrays.

Parameters:

  • fileName (string) – CAD file name

  • format (string) – file format (‘fmt_iges’ or ‘fmt_step’)

  • h (float) – step size on output mesh. If 0., automatic setting [algo=1,2].

  • chordal_error (float) – max error between CAD and mesh. Result in curvature adaptation. If 0., automatic setting.

  • growth_ratio (float) – max growth ratio between adjacent triangles [algo=1,2].

  • algo (int) – algo=0: mesh with only respect to curvature, algo=1 or algo=2: mesh with regular triangles.

Return type:

a list of TRI arrays

Example of use:

# - convertCAD2Arrays (arrays) -
import Converter as C
import OCC

# IGES avec T3Mesher
A = OCC.convertCAD2Arrays('hammer.iges', format='fmt_iges',
                          h=0., chordal_err=0., growth_ratio=0.8, algo=1)
C.convertArrays2File(A, 'hammer1.plt')

# IGES avec OCC
A = OCC.convertCAD2Arrays('hammer.iges', format='fmt_iges',
                          chordal_err=1, algo=0)
C.convertArrays2File(A, 'hammer2.plt')

# STEP avec T3Mesher
A = OCC.convertCAD2Arrays('as1-oc-214.stp', format='fmt_step',
                          h=0., chordal_err=0., growth_ratio=0.8, algo=1)
C.convertArrays2File(A, 'as1.plt')

# STEP avec OCC
A = OCC.convertCAD2Arrays('as1-oc-214.stp', format='fmt_step',
                          chordal_err=1, algo=0)
C.convertArrays2File(A, 'as2.plt')
OCC.PyTree.convertCAD2PyTree(fileName, format='fmt_iges', h=0., chordal_err=0., growth_ratio=0., algo=1)

Read a CAD and return a zone.

Parameters:

  • fileName (string) – CAD file name

  • format (string) – file format (‘fmt_iges’ or ‘fmt_step’)

  • h (float) – step size on output mesh. If 0., automatic setting [algo=1,2].

  • chordal_error (float) – max error between CAD and mesh. Result in curvature adaptation. If 0., automatic setting.

  • growth_ratio (float) – max growth ratio between adjacent triangles [algo=1,2].

  • algo (int) – algo=0: mesh with only respect to curvature, algo=1 or algo=2: mesh with regular triangles.

Return type:

CGNS pyTree

Example of use:

# - convertIGES2PyTree (PyTree) -
import OCC.PyTree as OCC
import Converter.PyTree as C

t = OCC.convertCAD2PyTree('hammer.iges', h=0., chordal_err=0., algo=1)
C.convertPyTree2File(t, 'out.cgns')

CAD manipulation

OCC.readCAD(fileName, format='fmt_step')

Read a CAD file and return a CAD hook.

Parameters:

  • fileName (string) – CAD file name

  • format (string) – file format (‘fmt_iges’ or ‘fmt_step’)

Return type:

CAD hook

Example of use:

# - readCAD (pyTree) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC.writeCAD(hook, fileName, format='fmt_step')

Write a CAD hook to a file.

Parameters:

  • hook (CAD hook) – CAD hook

  • fileName (string) – CAD file name

  • format (string) – file format (‘fmt_iges’ or ‘fmt_step’)

Example of use:

# - writeCAD (pyTree) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC.writeCAD(hook, "out.step", "fmt_step")
OCC.getNbEdges(hook)

Return the total number of edges in a CAD hook.

Parameters:

hook (CAD hook) – CAD hook

Return type:

int

Example of use:

# - getNbEdges (pyTree) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
print(OCC.getNbEdges(hook))
#> 12
OCC.getNbFaces(hook)

Return the number of faces in a CAD hook.

Parameters:

hook (CAD hook) – CAD hook

Return type:

int

Example of use:

# - getNbFaces (pyTree) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
print(OCC.getNbFaces(hook))
#> 6
OCC.getFaceArea(hook, listFaces=[])

Return the area of given faces.

Parameters:

  • hook (CAD hook) – CAD hook

  • listFaces (list of face index (starts 1)) – list of faces number to calculate the area

Return type:

float

Example of use:

# - getFaceArea (pyTree) -
import OCC.PyTree as OCC

h = OCC.readCAD('cube.step', 'fmt_step')

# Area of all model
print(OCC.getFaceArea(h))

# Area of seome faces
print(OCC.getFaceArea(h, [1,2]))
OCC._translate(hook, vector, listOfFaces=None)

Translate a CAD hook by a given vector.

Parameters:

  • hook (CAD hook) – CAD hook

  • vector (tuple of floats) – translation vector (dx, dy, dz)

  • listOfFaces (list of face indices (starts 1)) – if None, translate all else translate only given faces

Example of use:

# - translate (pyTre) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._translate(hook, (1,0,0))
OCC.writeCAD(hook, 'out.step', 'fmt_step')
OCC._rotate(hook, Xc, axis, angle, listOfFaces=None)

Rotate a CAD hook around a given axis by a given angle.

Parameters:

  • hook (CAD hook) – CAD hook

  • Xc (tuple of floats) – rotation center (x, y, z)

  • axis (tuple of floats) – rotation axis

  • angle (float) – rotation angle in degrees

  • listOfFaces (list of face indices (starts 1)) – if None, rotate all else rotate only given faces

Example of use:

# - rotate (pyTree) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._rotate(hook, (0,0,0), (0,0,1), 30.)
OCC.writeCAD(hook, 'out.step', 'fmt_step')
OCC._splitFaces(hook, area)

Split faces in a CAD hook.

Parameters:

  • hook (CAD hook) – CAD hook

  • area (float) – split each face if area greater than this value

Example of use:

# - splitFaces (pyTree) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._splitFaces(hook, 20.)
OCC.writeCAD(hook, "out.step", "fmt_step")
OCC._mergeFaces(hook, listFaces=None)

Merge faces in a CAD hook.

Parameters:

  • hook (CAD hook) – CAD hook

  • listFaces (list of face indices (starts 1)) – if None, merge all faces else list of faces indices to merge

Example of use:

# - mergeFaces (array) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._splitFaces(hook, 200.)
# merge given faces
OCC._mergeFaces(hook, [1,2,3])
# merge all faces
OCC._mergeFaces(hook)
OCC.writeCAD(hook, "out.step", "fmt_step")
OCC._sewing(hook, listFaces=None, tol=1.e-6)

Sew faces. Supress redundant edges.

Parameters:

  • hook (CAD hook) – CAD hook

  • listFaces (list of face indices (starts 1)) – if None, merge all faces else list of faces indices to merge

  • tol (float) – tolerance for sewing

Example of use:

# - sewing (pyTree) -
import OCC.PyTree as OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._sewing(hook, tol=1.e-6, listFaces=[1,2])
OCC._sewing(hook, tol=1.)
OCC.writeCAD(hook, 'out.step', 'fmt_step')