Geometry introduction

We can load a number of classes from the Geometry Procesor:

from OCC.gp import gp_Pnt, gp_Pln, gp_Dir

With those classes we can: 

# create points
pnt1 = gp_Pnt(0,0,0)

# create direction
dir1 = gp_Dir(0,0,1)

# create a plane
plan = gp_Pln(gp_Pnt(0,0,0), gp_Dir(0,0,1)) # Z=0 plan / XY plan

2D geometry

We can sketch in 2d geometry:

from OCC.Display.SimpleGui import init_display
from OCC.gp import gp_Lin2d, gp_Pnt2d, gp_Dir2d
from core_geometry_utils import make_edge2d

display, start_display, add_menu, add_function_to_menu = init_display()

# Creating 2d points
p1 = gp_Pnt2d(2.,3.)
p2 = gp_Pnt2d(2.,5.)
display.DisplayShape( p1 )
display.DisplayShape( p2, update=True )

# Creating a 2d line requires: a point and a direction
d1 = gp_Dir2d(1.,1.)
l1 = gp_Lin2d(p1, d1)
display.DisplayShape(make_edge2d(l1), update=True )

To draw a circle, something as follows:

from OCC.gp import gp_Circ2d, gp_Ax22d

# Draws a circle geometry using gp_Ax22d and radius=4
ci1 = gp_Circ2d(gp_Ax22d(), 4)
display.DisplayColoredShape(make_edge2d(ci1), update=True, color="BLUE" )

Let's talk about gp_Ax22d.

from OCC.GCE2d import GCE2d_MakeLine, GCE2d_MakeCircle
from OCC.GccAna import GccAna_Lin2dBisec, GccAna_CircLin2dBisec, GccAna_Pnt2dBisec

from OCC.gp import gp_Vec

Axis

core_geometry_axis.py

core_geometry_airfoil.py core_geometry_axis.py core_geometry_bisector.py core_geometry_bounding_box.py core_geometry_bspline.py core_geometry_curves2d_from_curve.py core_geometry_curves2d_from_offset.py core_geometry_face_recognition_from_stepfile.py core_geometry_faircurve.py core_geometry_geomplate.py core_geometry_medial_axis_offset.py core_geometry_minimal_distance.py core_geometry_parabola.py core_geometry_point_from_curve.py core_geometry_point_from_intersection.py core_geometry_project_point_on_curve.py core_geometry_quaternion.py core_geometry_splinecage.py core_geometry_surface_from_curves.py core_geometry_utils.py

Reading a STEP file

For example:

from OCC.STEPControl import STEPControl_Reader
step_reader = STEPControl_Reader()
step_reader.ReadFile('./mystep.stp')
step_reader.TransferRoot()
myshape = step_reader.Shape()

Then we can traverse the file searching elements inside. For instance, if we are looking for solids:

from OCC.TopExp import TopExp_Explorer
from OCC.TopAbs import TopAbs_SOLID

topExp = TopExp_Explorer()
topExp.Init(intake_shape, TopAbs_SOLID)

Now we can iterate over the explorer:

>>> from OCC.TopTools import TopTools_ListOfShape
>>> seq = []
>>> hashes = []
>>> occ_seq = TopTools_ListOfShape()
>>> topExp.More()
True
>>> item = topExp.Current()
>>> item
class<'TopoDS_Shape'; Type:Solid; id:916570656>
>>> dir(item)
['Checked', 'Closed', 'Complement', 'Complemented', 'Compose', 'Composed', 'Convex', 'EmptyCopied', 'EmptyCopy', 'Free', 'HashCode', 'Infinite', 'IsEqual', 'IsNotEqual', 'IsNull', 'IsPartner', 'IsSame', 'Located', 'Location', 'Locked', 'Modified', 'Move', 'Moved', 'Nullify', 'Orientable', 'Orientation', 'Oriented', 'Reverse', 'Reversed', 'ShapeType', 'TShape', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__eq_wrapper__', '__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__ne_wrapper__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setstate__', '__sizeof__', '__str__', '__subclasshook__', '__swig_destroy__', '__weakref__', 'this', 'thisown']
>>> item.__hash__()
916570656

The hash can be added into the python list, while the shape should be added into occ_seq = TopTools_ListOfShape():

hashes.append(item.__hash__())
occ_seq.Append(current_item)

Then we go to the following matching shape using: 

topExp.Next()

So we use:

  • topExp.Current(): to get the current shape
  • topExp.More(): in order to know if there are more shapes.
  • topExp.Next(): in order to go to the following shape.

The convenient class Topo is defined in core_topology_traverse.py. It is used in the example core_geometry_face_recognition_from_stepfile.py.

Viewing in a web page

To view a STEP file in the browser:

#!/usr/bin/env python
from OCC.STEPControl import STEPControl_Reader
from OCC.Display.WebGl import x3dom_renderer
from OCC.BRep import BRep_Builder
from OCC.TopoDS import TopoDS_Shape
from OCC.BRepTools import breptools_Read

# loads step
step_reader = STEPControl_Reader()
step_reader.ReadFile('mystep.stp')
step_reader.TransferRoot()
myshape = step_reader.Shape()

my_renderer = x3dom_renderer.X3DomRenderer()
my_renderer.DisplayShape(myshape)
my_renderer.render()

In order to view a BREP file:

# loads brep shape
cylinder_head = TopoDS_Shape()
builder = BRep_Builder()
breptools_Read(cylinder_head, './models/cylinder_head.brep', builder)

See the examples:

https://github.com/tpaviot/pythonocc-core/blob/0.18.1/examples/core_webgl_threejs_random_toruses.py

https://github.com/tpaviot/pythonocc-core/blob/0.18.1/examples/core_webgl_threejs_torus.py

http://www.pythonocc.org/resources/tutorial/gettin-started-with-pyqt-wxpython-and-pythonocc/

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