Open CASCADE Technology  7.4.0




Welcome to Open CASCADE Technology (OCCT), a software development platform providing services for 3D surface and solid modeling, CAD data exchange, and visualization. Most of OCCT functionality is available in the form of C++ libraries. OCCT can be best applied in development of software dealing with 3D modeling (CAD), manufacturing / measuring (CAM) or numerical simulation (CAE).


Open CASCADE Technology and all materials, including this documentation, is Copyright (c) 1999-2019 by OPEN CASCADE S.A.S. All rights reserved.



Open CASCADE Technology is free software; you can redistribute it and / or modify it under the terms of the GNU Lesser General Public License (LGPL) version 2.1, with additional exception.

Note that LGPL imposes some obligations on the application linked with Open CASCADE Technology. If you wish to use OCCT in a proprietary application, please pay a special attention to address the requirements of LGPL section 6. At minimum the following should be considered:

  1. Add the notice visible to the users of your application clearly stating that Open CASCADE Technology is used in this application, and that they have rights in this regard according to LGPL. Such notice can be added in About dialog box (this is mandatory if this box contains copyright statements) or a similar place and/or in the documentation. The text of LGPL license should be accessible to the user.
  2. Make the copy of OCCT sources used by the application available to its users, and if necessary provide instructions on how to build it in a way compatible with the application.
  3. Ensure that the user actually can exercise the right to run your application with a modified version of OCCT. If the application is distributed in a form that does not allow the user to modify OCCT part (e.g. the application is linked to OCCT statically or is distributed via AppStore on iOS, GooglePlay on Android, Windows Store, etc.), the application should be provided separately in a modifiable form, with all materials needed for the user to be able to run the application with a modified version of OCCT.

If you want to use Open CASCADE Technology without being bound by LGPL requirements, please contact Open CASCADE company for a commercial license.

Note that Open CASCADE Technology is provided on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND. The entire risk related to any use of the OCCT code and materials is on you. See the license text for formal disclaimer.

Trademark information

You are hereby informed that all software is a property of its respective authors and is protected by international and domestic laws on intellectual property and trademarks. Should you need further information, directly contact the authors.

CAS.CADE and Open CASCADE are registered trademarks of OPEN CASCADE S.A.S.

Linux is a registered trademark of Linus Torvalds.

Windows is a registered trademark of Microsoft Corporation in the United States and other countries.

Mac and the Mac logo are trademarks of Apple Inc., registered in the U.S. and other countries.


The following parties are acknowledged for producing tools which are used within Open CASCADE Technology libraries or for release preparation.

You are hereby informed that all rights to the software listed below belong to its respective authors and such software may not be freely available and/or be free of charge for any kind of use or purpose. We strongly recommend that you carefully read the license of these products and, in case you need any further information, directly contact their authors.

Qt is a cross-platform application framework that is widely used for developing application software with graphical user interface (GUI). Qt is free and open source software distributed under the terms of the GNU Lesser General Public License. In OCCT Qt is used for programming samples. If you need further information on Qt, refer to Qt Homepage (

Tcl is a high-level programming language. Tk is a graphical user interface (GUI) toolkit, with buttons, menus, listboxes, scrollbars, and so on. Taken together Tcl and Tk provide a solution to develop cross-platform graphical user interfaces with a native look and feel. Tcl/Tk is under copyright by Scriptics Corp., Sun Microsystems, and other companies. However, Tcl/Tk is an open source, and the copyright allows you to use, modify, and redistribute Tcl/Tk for any purpose, without an explicit license agreement and without paying any license fees or royalties. To use Tcl/Tk, refer to the Licensing Terms (

FreeType 2 is developed by Antoine Leca, David Turner, Werner Lemberg and others. It is a software font engine that is designed to be small, efficient, highly customizable and portable while capable of producing high-quality output (glyph images). This product can be used in graphic libraries, display servers, font conversion tools, text image generation tools, and many other products. FreeType 2 is released under two open-source licenses: BSD-like FreeType License and the GPL (

Intel(R) Threading Building Blocks (TBB) offers a rich and complete approach to expressing parallelism in a C++ program. It is a library that helps you to take advantage of multi-core processor performance without having to be a threading expert. Threading Building Blocks is not just a threads-replacement library. It represents a higher-level, task-based parallelism that abstracts platform details and threading mechanisms for scalability and performance. TBB version 2017 is available under Apache 2.0 license, while older versions until 4.4 are available under GPLv2 license with the runtime exception (

OpenGL is an industry standard API for 3D graphics used by OCCT for implementation of 3D viewer. OpenGL specification is developed by the Khronos group, OCCT code includes header file glext.h obtained from Khronos web site.

VTK – The Visualization Toolkit (VTK) is an open-source, freely available software system for 3D computer graphics, image processing and visualization. OCCT VIS component provides adaptation functionality for visualization of OCCT topological shapes by means of VTK library. If you need further information on VTK, refer to VTK Homepage

Doxygen developed by Dimitri van Heesch is open source documentation system for C++, C, Java, Objective-C, Python, IDL, PHP and C#. This product is used in Open CASCADE Technology for automatic creation of Technical Documentation from C++ header files. If you need further information on Doxygen, refer to

Graphviz is open source graph visualization software developed by John Ellson, Emden Gansner, Yifan Hu and Arif Bilgin. Graph visualization is representiation of structured information as diagrams of abstract graphs and networks. This product is used together with Doxygen in Open CASCADE Technology for automatic creation of Technical Documentation (generation of dependency graphs). Current versions of Graphviz are licensed on an open source basis under The Eclipse Public License (EPL) (

Inno Setup is a free script-driven installation system created in CodeGear Delphi by Jordan Russell. In OCCT Inno Setup is used to create Installation Wizard on Windows. It is licensed under Inno Setup License (

FreeImage is an Open Source library supporting popular graphics image formats, such as PNG, BMP, JPEG, TIFF, and others used by multimedia applications. This library is developed by Hervé Drolon and Floris van den Berg. FreeImage is easy to use, fast, multithreading safe, compatible with all 32-bit or 64-bit versions of Windows, and cross-platform (works both with Linux and Mac OS X). FreeImage is optionally used by OCCT to work with images, on conditions of the FreeImage Public License (FIPL) (

David M. Gay's floating point routines (dtoa.c) are used for fast reading of floating point values from text strings. These routines are available under MIT-like license (see

CMake is an open-source, cross-platform family of tools designed to build, test and package software. CMake is used to control the software compilation process using simple platform and compiler independent configuration files, and generate native makefiles and workspaces that can be used in the compiler environment of your choice. OCCT uses CMake as a build system. CMake is available under BSD 3-Clause license. See more at

Cotire (compile time reducer) is a CMake module that speeds up the build process of CMake based build systems by fully automating techniques as precompiled header usage and single compilation unit builds for C and C++. Cotire is included in OCCT repository and used optionally by OCCT CMake scripts to accelerate builds by use of precompiled headers. Cotire is licensed under the MIT license (

FFmpeg is an Open Source framework supporting various image, video and audio codecs. FFmpeg is optionally used by OCCT for video recording, on LGPL conditions (

MikTEX is up-to-date implementation of TeX/LaTeX and related programs for Windows. It is used for generation of User and Developer Guides in PDF format. See for information on this tool.

RapidJSON is an Open Source JSON parser and generator for C++. RapidJSON is optionally used by OCCT for reading glTF files (

Adobe Systems, Inc. provides Adobe Reader, which can be used to view files in Portable Document Format (PDF).


OCCT documentation is provided in several forms:

  • This overview provides general description of OCCT structure, functionality, modules, and features. It is available in HTML format (generated by Doxygen) and includes User and Developer Guides. The sources of this documentation are contained in dox subdirectory of OCCT sources (plain text format is used, with mixed MarkDown / Doxygen syntax mark-up).
  • User and Developer Guides describing in details OCCT modules and development tools are also available in Adobe Portable Document Format (PDF). To read this format, you need Adobe Acrobat Reader, which is a freeware and can be downloaded from the Adobe site.
  • Full reference documentation covering all OCCT classes generated automatically by Doxygen software is provided in HTML format. Reference documentation is presented in Modules –> Toolkits –> Packages –> Classes logic structure with cross-references to all OCCT classes and complete in-browser search by all classes.

See OCCT Documentation Guide for details on OCCT documentation system.

Generation of HTML documentation

To generate HTML documentation from sources contained in dox subdirectory, you need to have Tcl and Doxygen 1.8.5 (or above) installed on your system.

Use script gendoc (batch file on Windows, shell script on Linux / Mac OSX) to generate documentation.

To generate Overview documentation:

cmd> gendoc -overview

To generate Reference manual:

cmd> gendoc -refman

Run this command without arguments to get help on supported options.


Open CASCADE Technology is designed to be highly portable and is known to work on wide range of platforms. Current version is officially certified on Windows (IA-32 and x86-64), Linux (x86-64), OS X / macOS (x86-64), Android (armv7 and x86), and iOS (armv7, arm64) platforms.

The tables below describe the recommended software configurations for which OCCT is certified to work.

C++ Compiler / IDE

OS Compiler
Windows Microsoft Visual Studio: 2008 SP1, 2010 SP1, 2012 Update 4, 2013 Update 5, 2015 Update 3, 2017 1,
GCC 4.3+ (Mingw-w64)
Linux GNU gcc 4.3+
LLVM CLang 3.6+
OS X / macOS XCode 6 or newer
Android NDK r10, GNU gcc 4.8 or newer

1) VC++ 141 64-bit is used for regular testing and for building binary package of official release of OCCT on Windows.

Third-party libraries

Component Requirement
Graphic library OpenGL 3.3+, OpenGL ES 2.0+
Direct3D 9
Qt (for samples and demos) Desktop: Qt 4.8.6+
Android: Qt 5.3.2+
TCL (for testing tools) Tcl/Tk 8.6.3+
or ActiveTcl 8.6 (for Windows)
Freetype (for text rendering) FreeType 2.4.11-2.7.1
FreeImage (optional, for support of common 2D graphic formats) FreeImage 3.17.0+
FFmpeg (optional, for video recording) FFmpeg 3.1+
RapidJSON (optional, for reading glTF) RapidJSON 1.1+
Intel TBB (optional, for multithreaded algorithms) TBB 4.x or 5.x
VTK (for VTK Integration Services VTK 6.1+
Doxygen (optional for building documentation) Doxygen 1.8.5+


Component Requirement
Minimum memory 512 MB, 1 GB recommended
Free disk space (complete installation) 600 MB approx.

On desktop, 3D viewer for optimal performance requires graphics processing unit (GPU) supporting OpenGL 3.3 or above. Ray tracing requires OpenGL 4.0+ or OpenGL 3.3+ with GL_ARB_texture_buffer_object_rgb32 extension. Textures within ray tracing will be available only when GL_ARB_bindless_texture extension is provided by driver.

On mobile platforms, OpenGL ES 2.0+ is required for 3D viewer (OpenGL ES 3.1+ is recommended). The ray tracing is not yet available on mobile platforms. Some old hardware might be unable to execute complex GLSL programs (e.g. with high number of light sources, clipping planes).

OCCT 3D Viewer, in general, supports wide range of graphics hardware - from very old to new. Therefore, if you observe some unexpected visual issues - first check for OpenGL driver update (or firmware update in case of mobile platforms); but beware that driver update might also come with new bugs. Don't forget to report these bugs to vendors.


In most cases you need to rebuild OCCT on your platform (OS, compiler) before using it in your project, to ensure binary compatibility. See Building OCCT from sources for instructions on building OCCT from sources on supported platforms.

Using Windows installer

On Windows Open CASCADE Technology can be installed with binaries precompiled by Visual C++ 2010 with installation procedure.


If you have a previous version of OCCT installed on your station, and you do not plan to use it along with the new version, you might want to uninstall the previous version (using Control Panel, Add/Remove Programs) before the installation of this new version, to avoid possible problems (conflict of system variables, paths, etc).

Attention: For full installation OCCT requires approximately 650 Mb of disk space, but during the installation process you will need 1,2 Gb of free disk space.

OCCT installation with reference documentation requires 1,4 Gb on disk.

  • Download the OCCT installer from OPEN CASCADE web site using the link. you have been provided
  • Launch the installer and follow the instructions.

The includes and binaries of third-party libraries necessary for building and launching OCCT are included into binary distribution (built with Visual C++ 2010). When the installation is complete, you will find the directories for 3rd party products (some might be absent in case of custom installation) and the main OCCT directory:


The contents of the OCCT-7.4.0 directory (called further "OCCT root", or $CASROOT) are as follows:

The directory tree
  • adm This folder contains administration files, which allow rebuilding OCCT;
  • adm/cmake This folder contains files of CMake building procedure;
  • adm/msvc This folder contains Visual Studio projects for Visual C++ 2010, 2012, 2013, 2015, 2017 and 2019 which allow rebuilding OCCT under Windows platform in 32 and 64-bit mode;
  • data This folder contains CAD files in different formats, which can be used to test the OCCT functionality;
  • doc This folder contains OCCT documentation in HTML and PDF format;
  • dox This folder contains sources of OCCT documentation in plain text (MarkDown) format;
  • inc This folder contains copies of all OCCT header files;
  • samples This folder contains sample applications.
  • src This folder contains OCCT source files. They are organized in folders, one per development unit;
  • tests This folder contains scripts for OCCT testing.
  • tools This folder contains sources of Inspector tool.
  • win64/vc10 This folder contains executable and library files built in optimize mode for Windows platform by Visual C++ 2010;

Environment Variables

To run any Open CASCADE Technology application you need to set the environment variables.

On Windows

You can define the environment variables with env.bat script located in the $CASROOT folder. This script accepts two arguments to be used: the version of Visual Studio (vc10 – vc142) and the architecture (win32 or win64).

The additional environment settings necessary for compiling OCCT libraries and samples by Microsoft Visual Studio can be set using script custom.bat located in the same folder. You might need to edit this script to correct the paths to third-party libraries if they are installed on your system in a non-default location.

Script msvc.bat can be used with the same arguments for immediate launch of Visual Studio for (re)compiling OCCT.

On Unix

If OCCT was built by Code::Blocks, you can define the environment variables with or script.

If OCCT was built by Automake, you can define the environment variables with or script.

The scripts are located in the OCCT root folder.

Description of system variables:

  • CASROOT is used to define the root directory of Open CASCADE Technology;
  • PATH is required to define the path to OCCT binaries and 3rdparty folder;
  • LD_LIBRARY_PATH is required to define the path to OCCT libraries (on UNIX platforms only; DYLD_LIBRARY_PATH variable in case of macOS);
  • MMGT_OPT (optional) if set to 1, the memory manager performs optimizations as described below; if set to 2, Intel (R) TBB optimized memory manager is used; if 0 (default), every memory block is allocated in C memory heap directly (via malloc() and free() functions). In the latter case, all other options starting with MMGT, except MMGT_CLEAR, are ignored;
  • MMGT_CLEAR (optional) if set to 1 (default), every allocated memory block is cleared by zeros; if set to 0, memory block is returned as it is;
  • MMGT_CELLSIZE (optional) defines the maximal size of blocks allocated in large pools of memory. Default is 200;
  • MMGT_NBPAGES (optional) defines the size of memory chunks allocated for small blocks in pages (operating-system dependent). Default is 10000;
  • MMGT_THRESHOLD (optional) defines the maximal size of blocks that are recycled internally instead of being returned to the heap. Default is 40000;
  • MMGT_MMAP (optional) when set to 1 (default), large memory blocks are allocated using memory mapping functions of the operating system; if set to 0, they will be allocated in the C heap by malloc();
  • CSF_LANGUAGE (optional) defines default language of messages;
  • CSF_DEBUG (optional, Windows only): if defined then a diagnostic message is displayed in case of an exception;
  • CSF_DEBUG_BOP (optional): if defined then it should specify directory where diagnostic data on problems occured in Boolean operations will be saved;
  • CSF_MDTVTexturesDirectory defines the directory for available textures when using texture mapping;
  • CSF_ShadersDirectory (optional) defines the directory for GLSL programs for Ray Tracing renderer (embedded resources are used when variable is undefined);
  • CSF_SHMessage (optional) defines the path to the messages file for ShapeHealing;
  • CSF_XSMessage (optional) defines the path to the messages file for STEP and IGES translators;
  • CSF_StandardDefaults, CSF_StandardLiteDefaults*, **CSF_XCAFDefaults, and CSF_PluginDefaults define paths to directory where configuration files for OCAF persistence are located (required for open/save operations with OCAF documents);
  • CSF_IGESDefaults and CSF_STEPDefaults (optional) define paths to directory where resource files of IGES and STEP translators are located;
  • CSF_XmlOcafResource is required in order to set the path to XSD resources, which defines XML grammar.
  • CSF_MIGRATION_TYPES is required in order to read documents that contain old data types, such as TDataStd_Shape;

Getting Started

Draw Test Harness

Draw is a command interpreter based on TCL and a graphical system used for testing and demonstrating OCCT modeling libraries.

Draw can be used interactively to create, display and modify objects such as curves, surfaces and topological shapes.


Scripts can be written to customize Draw and perform tests. New types of objects and new commands can be added using C++ programming language.

Draw contains:

  • A command interpreter based on TCL command language.
  • A 2D an 3D graphic viewer with support of operations such as zoom, pan, rotation and full-screen views.
  • An optional set of geometric commands to create and modify curves and surfaces and to use OCCT geometry algorithms.
  • A set of topological commands to create and modify BRep shapes and to use OCCT topology algorithms.
  • A set of graphic commands for view and display operations including Mesh Visualization Service.
  • A set of Application framework commands for handling of files and attributes.
  • A set of Data Exchange commands for translation of files from various formats (IGES,STEP) into OCCT shapes.
  • A set of Shape Healing commands: check of overlapping edges, approximation of a shape to BSpline, etc.

You can add new custom test harness commands to Draw in order to test or demonstrate a new functionality, which you are developing.

Currently DRAW Test Harness is a single executable called DRAWEXE.

Commands grouped in toolkits can be loaded at run-time thereby implementing dynamically loaded plug-ins. Thus you can work only with the commands that suit your needs adding the commands dynamically without leaving the Test Harness session.

Declaration of available plug-ins is done through special resource file(s). The pload command loads the plug-in in accordance with the specified resource file and activates the commands implemented in the plug-in.

The whole process of using the plug-in mechanism as well as the instructions for extending Test Harness is described in the Draw Test Harness.

Draw Test Harness provides an environment for OCCT automated testing system. Check its Automated Testing System for details.


  • The DRAWEXE executable is delivered with the installation procedure on Windows platform only.
  • To start it, launch DRAWEXE executable from Open CASCADE Technology/Draw Test Harness item of the Start\Programs menu.

Experimenting with Draw Test Harness

Running Draw

On Linux:

  • If OCCT was built by Code::Blocks use $CASROOT/ file to launch DRAWEXE executable.

Draw[1]> prompt appears in the command window

Type pload ALL

On Windows:

Launch Draw executable from Open CASCADE Technology\Test Harness\Draw Test Harness item of the Start\Programs menu or Use $CASROOT\draw.bat file to launch DRAWEXE executable.

Draw[1]> prompt appears in the command window

Type pload ALL

Creating your first geometric objects

  1. In the command window, type axo to create an axonometric view
  2. Type box b -10 -10 -10 20 20 20 to create a cube b of size 20, parallel to the X Y Z axis and centered on the origin. The cube will be displayed in the axonometric view in wireframe mode.
  3. Type fit to fill the viewer with the cube
  4. Type pcylinder c 2 30 to create a cylinder c of radius 2 and height 30. The cylinder will be displayed in addition to the cube

Manipulating the view

  1. Type clear to erase the view
  2. Type donly c to display the cylinder only
  3. Type donly b to display the cube only
  4. Type hlr hlr b to display the cube in the hidden line removal mode

Running demonstration files

  1. Type cd ../.. to return to the root directory
  2. Type cd samples/tcl to reach the DrawResources directory
  3. Type source <demo_file> to run the demonstration file provided with Open CASCADE. The following demonstration files are available:
    • DataExchangeDemo.tcl: demonstrates sample sequence of operations with writing and reading IGES file
    • ModelingDemo.tcl: demonstrates creation of simple shape and displaying it in HLR mode
    • VisualizationDemo.tcl: demonstrates use of 3d viewer
    • cad.tcl: creates solid shape looking like abbreviation "CAD"
    • bottle.tcl: creates bottle as in OCCT Tutorial
    • drill.tcl: creates twist drill bit shape
    • cutter.tcl: creates milling cutter shape
    • xde.tcl: demonstrates creation of simple assembly in XDE
    • materials.tcl: demonstrates visual properties of materials supported by 3d viewer
    • raytrace.tcl: demonstrates use of ray tracing display in 3d viewer
    • dimensions.tcl: demonstrates use of dimensions, clipping, and capping in 3d viewer

Getting Help

  1. Type help to see all available commands
  2. Type help <command_name> to find out the arguments for a given command

Programming Samples


Visual C++ programming samples containing 10 Visual C++ projects illustrating how to use a particular module or functionality.

The list of MFC samples:

  • Geometry
  • Modeling
  • Viewer2d
  • Viewer3d
  • ImportExport
  • Ocaf
  • Triangulation
  • HLR
  • Animation
  • Convert


  • MFC samples are available only on Windows platform;
  • To start a sample use Open CASCADE Technology\Samples\Mfc\ item of the Start\Programs menu;
  • Read carefully readme.txt to learn about launching and compilation options.

See Readme for details.


OCCT contains three samples based on Qt application framework

Import Export

Import Export programming sample contains 3D Viewer and Import / Export functionality.



The Qt programming tutorial teaches how to use Open CASCADE Technology services to model a 3D object. The purpose of the tutorial is not to explain all OCCT classes but to help start thinking in terms of the Open CASCADE Technology.

This tutorial assumes that the user has experience in using and setting up C++. From the viewpoint of programming, Open CASCADE Technology is designed to enhance user's C++ tools with high performance modeling classes, methods and functions. The combination of these resources allows creating substantial applications.

See also: OCCT Tutorial


  • Qt samples are available on all supported platforms;
  • To start a sample on Windows use Open CASCADE Technology\Samples\Qt\ item of the Start\Programs menu.


C# sample demonstrates integration of OCCT 3D Viewer and Import / Export functionality into .NET applications (using Windows Forms and WPF front ends).



  • BRep
  • Iges
  • Step


  • Brep
  • Iges
  • Step
  • Stl
  • Vrml

See C# sample Readme for details.

There is also another C# example with the same functionality, which demonstrates the integration of Direct3D Viewer into .NET applications using WPF front end.

See Direct3D C# sample Readme for details.


There are two samples are representing usage OCCT framework on Android mobile platform. They represent an OCCT-based 3D-viewer with CAD import support in formats BREP, STEP and IGES: jniviewer (java) and AndroidQt (qt+qml)



Java – See Android Java sample Readme for details.



Qt – See Android Qt sample Readme for details.


There is a sample demonstrating usage of OCCT on iOS with Apple UIKit framework.


See iOS sample Readme for details.