Creating a Closed Wire in PythonOCC

PythonOCC is a powerful library for 3D CAD development, enabling users to create and manipulate complex geometric shapes with ease. In this tutorial, we'll walk through the process of creating a simple closed wire using PythonOCC. 

Setting up PythonOCC

First, ensure PythonOCC is installed and properly set up in your environment. PythonOCC can be used in conjunction with OpenCASCADE, a comprehensive open-source 3D CAD development toolkit.

Code Walkthrough

Our goal here is to create a closed wire – a basic shape in CAD modeling. We'll form a square loop as an example. 

Step 1: Import Required Libraries

import os
from OCC.Core.gp import gp_Pnt
from OCC.Core.BRepBuilderAPI import BRepBuilderAPI_MakePolygon
from OCC.Display.SimpleGui import init_display

We begin by importing necessary modules. We add a specific directory to the DLL search path to ensure our program finds the OpenCASCADE libraries. gp_Pnt is used for defining 3D points, BRepBuilderAPI_MakePolygon for creating the wire, and init_display for visualization. 

Step 2: Define Points

points = [
    gp_Pnt(0, 0, 0),
    gp_Pnt(10, 0, 0),
    gp_Pnt(10, 10, 0),
    gp_Pnt(0, 10, 0)
]

Here, we define the vertices of our square. Each point is an instance of gp_Pnt, which takes three coordinates (X, Y, Z). 

 Step 3: Create the Wire

polygon_builder = BRepBuilderAPI_MakePolygon()
for point in points:
    polygon_builder.Add(point)
polygon_builder.Close()

We use BRepBuilderAPI_MakePolygon to build our wire. Points are added sequentially with the Add method. The Close method then connects the last point back to the first, closing our loop. 

 Step 4: Retrieve the Wire

closed_wire = polygon_builder.Wire()

The Wire method retrieves the constructed wire from our builder object.

 Step 5: Initialize the Display

display, start_display, add_menu, add_function_to_menu = init_display()

We initialize the display system of PythonOCC. This step sets up the GUI elements for visualization.

 Step 6: Display the Wire

display.DisplayShape(closed_wire, update=True)
display.FitAll()

The wire is displayed using DisplayShape. We also adjust the view to fit the entire shape using FitAll.

 Step 7: Start the Display Loop

start_display()

Finally, we enter the display loop. This part is crucial as it starts the GUI application and displays our wire.

 Step 8: Result

Conclusion

You've now created a simple closed wire and visualized it using PythonOCC. This tutorial covers the basics, but PythonOCC's capabilities extend far beyond this. Experiment with different shapes and complexities to explore the power of 3D CAD programming with PythonOCC.

Remember, to run this code, ensure you have PythonOCC installed and properly configured on your system. Happy coding!