OCCT DRAW and DE Commands Guide (ika authored)

[dpasukhi]

OCCT DRAW Commands Guide

How to Find a Necessary Command?

If you know a part of the name, you can use help and a wildcard *. For example, if you are looking for a command related to faces, use:

help *face*

This will return several command names, including mkface.

Note: DRAW commands and searches are case-sensitive.

How to Import and Export Files?

The easiest way to import a file is to call the DE Wrapper command, which imports the file into an XCAF model:

ReadFile Doc path_to_file
readfile shape path_to_file

Each format also has its own commands. Uppercase commands work with XCAF, while lowercase commands operate on shapes. Examples:

ReadStep stepread

Exceptions: Importing XBF and BREP uses:

XOpen  # For XBF
restore # For BREP

To export a file, use:

WriteFile Doc path_to_file
writefile shape path_to_file

Other writing commands:

SaveAs # For XCAF
save   # For BREP

How to Check Import and Shape Statistics?

Key commands:

data c   # Shows import warnings and failures
tpstat c # Provides additional statistics

Shape or document info:

XStat   # Check XCAF document data
whatis  # Inspect a shape
nbshapes # Check shape composition

How to Look into an XCAF Document?

Options for inspecting an XCAF document:

• DFBrowse - Opens the document in a new window.
• Inspector Tool - More advanced; built with OCCT. Start with inspector.bat.

How to Visualize a Shape?

Several options are available:

Basic Viewer:

• small / axo - Opens a simple viewer.
• Isolines: isos
• Normals: normals
• Shared edges (yellow), unshared edges (red)
• Controls: l, d, r, u (rotation), fit, wzoom

3D Viewer:

• vinit - General 3D viewer
• XShow - XCAF-specific 3D viewer
• Display shapes: vdisplay, vdonly, verase, vclear
• Change mode: vsetdispmode

2D Viewer:

• av2d - Opens a 2D viewer for pcurves
• Show pcurves: pcurve

Multi-View:

• mu4 - Splits into 4 views (3 projections + axo)

How to Work with XCAF Document Data?

XCAF tool methods exposed in DRAW start with X. Use:

help X*

Useful commands:

XGetOneShape, XGetShape, XAddShape, XFindShape, XUpdateAssemblies

How to Localize a Problem in a Large Shape?

If a geometric issue exists in a large shape, it needs to be isolated. The most useful format for debugging is STEP.

1. Read the file:

   ReadStep Doc filename.stp
   

2. Find problematic shape:

   checkshape   # Detect issues
   explode      # Break down shape into components
   erase .      # Remove parts selectively
   

3. Find the original entity:

   fromshape sh   # Identifies corresponding STEP entity
   entity 123 2   # Shows entity dependencies
   

4. Partial Import for Faster Debugging:

   stepread filename.stp a
   Mode: 3
   Entity: 123
   

   This imports only the problematic entity as a new shape.

How to Automate Work?

To execute TCL scripts from DRAW, use:

source script.tcl

This allows for automation of common tasks in OCCT.

How to Modify and Analyze Shapes?

Constructing and Modifying Shapes

You can create and modify geometry directly in DRAW.

• Creating Shapes:

  mkedge e 0 0 0 1 0 0   # Creates an edge
  mkface f e             # Creates a face from the edge
  

• Modifying Shapes:

  fuse a b result   # Boolean union
  cut a b result    # Boolean difference
  common a b result # Boolean intersection
  

• Transforming Shapes:

  translate shape 10 0 0  # Moves shape along X-axis
  rotate shape 0 0 0 1 0 0 90  # Rotates shape 90° around X-axis
  

Analyzing Shape Properties

• Checking Geometry Issues:

  checkshape shape  # Identifies issues
  

• Measuring Distances:

  dist a b  # Computes the distance between two shapes
  

• Getting Shape Information:

  bounding a  # Gets bounding box
  nbshapes a  # Counts sub-shapes
  

Guide to Data Exchange (DE) in OCCT

What is Data Exchange (DE)?

Data Exchange in Open CASCADE Technology (OCCT) refers to reading data from external files into OCCT's internal model and writing data back to files. This involves handling various file formats and transforming data between different representations.

Building

General Building Tips

• For OCCT BRep types like STEP or IGES, no additional configuration is required in CMake.
• For mesh formats (e.g. GLTF), RapidJSON is needed.

Debugging

Different formats have unique implementations. Mastering one format does not necessarily imply familiarity with others. Below are some general debugging strategies.

Documentation

While most issues can be solved without documentation, there are cases where consulting resources is necessary.

• Each specification format documentation is available online.
• Standard references and recommended practices exist for STEP.

Reading Process

Reading consists of multiple steps:

1. Identify the appropriate reading command in Draw (e.g., help *stl* to find readstl). Or use common DE Wrapper (readfile and writefile for shapes, ReadFile, WriteFile for documents)
2. Locate the command’s source code (getsource readstl).
3. Follow the method call hierarchy to find the reader's entry point.

Parsing Files

Parsing converts file to internal representation, needed only to transfer.

Common parsing issues:

• Invalid schema
• Corrupted file content

Translation

Translation converts parsed data into OCCT structures:

• Basic translation: Direct conversion to TopoDS_Shape, losing metadata.
• Advanced translation: Includes metadata (e.g., XCAF document for colors, names, layers).

Shape Healing

Shape healing adapts imported shapes for compatibility with OCCT algorithms. It involves processes like:

• Fixing topology errors.
• Adjusting geometry.
• Resolving issues with degenerated edges.

Writing Process

Writing involves:

1. Pre-processing: Adjusting shapes for format compatibility.
2. Translation: Converting OCCT data into the target format.
3. File Creation: Exporting to a file.

Testing

OCCT uses structured test grids (e.g., de, de_mesh). Standard workflows involve reading, writing, and comparing data integrity.

Author:
@ikochetkova