OCC: interface to open-cascade

Preamble

OCC performs reading of IGES or STEP files with open-cascade. It returns a triangular mesh.

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/surface mesh conversion

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 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.

Contents

CAD/mesh conversion

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:

• Read a CAD (array):

# - 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:

• Read a CAD (pyTree):

# - 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:

• Read a CAD:

# - readCAD (array) -
import 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:

• Write a CAD:

# - writeCAD (array) -
import OCC

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

---

OCC.getNbEdges(hook)

Return the number of edges in a CAD hook.

Parameters:

hook (CAD hook) – CAD hook

Return type:

int

Example of use:

• Get the number of edges:

---

OCC.getNbFaces(hook)

Return the number of faces in a CAD hook.

Parameters:

hook (CAD hook) – CAD hook

Return type:

int

Example of use:

• Get the number of faces:

---

OCC._translate(hook, vector)

Translate a CAD hook by a given vector.

Parameters:

• hook (CAD hook) – CAD hook

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

Example of use:

• Translate a CAD:

# - translate (array) -
import OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._translate(hook, (1,0,0))
OCC._translate(hook, (0,5,0), listFaces=[1])
OCC.writeCAD(hook, 'out.step', 'fmt_step')

---

OCC._rotate(hook, Xc, axis, angle)

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

Example of use:

• Rotate a CAD:

# - rotate (array) -
import OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._rotate(hook, (0,0,0), (0,0,1), 30.)
OCC._rotate(hook, (0,0,0), (0,0,1), 30., listFaces=[1])
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 face if area greater than this value

Example of use:

• Split faces:

# - splitFaces (array) -
import OCC

hook = OCC.readCAD("cube.step", "fmt_step")
OCC._splitFaces(hook, 20.)
OCC.writeCAD(hook, "out.step", "fmt_step")

---

OCC._mergeFaces(hook, listFaces=[])

Merge faces in a CAD hook.

Parameters:

• hook (CAD hook) – CAD hook

• listFaces (list of integers) – list of faces number to merge.

Example of use:

• Merge faces:

# - mergeFaces (array) -
import 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.getFaceArea(hook, listFaces=[])

Return the area of given faces.

Parameters:

• hook (CAD hook) – CAD hook

• listFaces (list of integers starting from 1) – list of faces number to calculate the area.

Return type:

float

Example of use:

• Get face area:

# - getFaceArea (array) -
import 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]))