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A toolkit for visual computing with a focus on geometry processing
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A toolkit for visual computing with a focus on geometry processing.

Author: Siddhartha Chaudhuri. Released under the BSD license (see Thea/Code/Documentation/LICENSE.txt).

If you find a bug, please let me know promptly. Thank you!

What is Thea?

Thea is a library of C++ classes for computer graphics, primarily for 3D geometry processing. It is the core library I use for nearly all my research projects, and it is also the core library for Adobe Fuse, which I originally authored. As such, it is developed for personal use and its features reflect this: please do not write to me to asking for specific features to be included. However, over time, it has become quite general-purpose. Among its features are:

  • Polygon mesh classes with arbitrary per-element attributes, including heavyweight ones that store full mesh topology and a lightweight one designed only for rendering.
  • General linear algebra via Eigen, geometric transformations (e.g. rigid transforms), shared-library-safe pure virtual wrappers for matrices, and easy-to-use interfaces to various solver packages (NNLS, CSPARSE, ARPACK).
  • 2, 3 and N-dimensional geometric primitives, including lines, line segments, rays, (hyper)planes, triangles (+ ray-triangle and triangle-triangle intersections), balls, axis-aligned boxes, oriented boxes, polygons and spline curves (+ fast spline-fitting to points).
  • An eclectic collection of algorithms, including a fast N-dimensional KD-tree (on points or mesh triangles), shortest paths in graphs, best-fit boxes and ellipsoids, singular value decomposition and PCA, iterative closest point (ICP), symmetry detection, convex hulls, connected components, discrete exponential maps, discrete Laplace-Beltrami operators on meshes, sampling points from meshes, mesh features (curvature, distance histogram, shape diameter, spin image), and some machine learning models.
  • Basic image processing (wrapper for FreeImage).
  • A plugin architecture and included plugins providing easy interfaces to OpenGL, ARPACK and CSPARSE. The OpenGL plugin optionally (and easily) compiles with an OSMesa driver to automatically create a headless CPU-only context.
  • A variety of utility classes for filesystem navigation, serialization, timing, synchronization, hashing, logging, string manipulation/searching, memory allocation, bounded/sorted arrays, pseudo-random numbers, mathematics (including algebraic roots of polynomials upto degree 4) etc.
  • Several bundled tools for 3D file viewing and annotation (Browse3D); offline rendering (RenderShape); mesh sampling (MeshSample), repair (MeshFix), features (MeshLocalFeatures, MeshGlobalFeatures) and format conversion (MeshConv); rigid (ShapeAlign) and non-rigid (Register) shape registration; k-NN graphs of surface samples (SampleGraph) etc.

Thea is constantly under development and many parts are incomplete. Use at your own risk! I do not provide any support (unless you have bugs to report), and I make no correctness or robustness guarantees for any part of the code. Parts of the library are reasonably battle-tested (e.g. in Fuse), and parts are one-off inclusions rarely used in anger or tested thoroughly.

Thea is heavily influenced by, and borrows code from, Morgan McGuire's G3D library. It started out as an extension of G3D.

The Thea library is not related to the independently and contemporaneously developed Thea Render photorealistic rendering engine.


Thea is written in standards-compliant C++11, and should compile with any recent compiler on Mac, Linux and Windows. It uses CMake as a cross-platform buildsystem. However, I do not normally work on Windows, and do not currently provide build instructions for this platform. I have successfully done Windows builds in the past and there is no reason why it should not work with a bit of effort getting the dependencies installed. I will try to add full Windows instructions in the future, time permitting.

Installing the dependencies

Thea relies on Boost, Eigen, lib3ds, FreeImage and ARPACK. A convenient script installs all of these on Unix-like systems (Mac and Linux), as follows. Both local (no root) and system-wide (needs root) installs are supported.

Assume $basedir is some directory where you're going to check out the source code, and $prefix is some directory where you'll install stuff (e.g. $basedir/Installations or /usr/local).

cd "$basedir"
git clone --recursive TheaDepsUnix
cd TheaDepsUnix/Source

For a local install (no root perms needed to write to $prefix):

./ --with-wxwidgets --prefix "$prefix" -j4

For a system-wide install:

sudo ./ --with-wxwidgets --use-root --prefix "$prefix" -j4

--use-root will try to use apt-get on Ubuntu/Debian, omit it if you want to build everything from scratch regardless. --with-wxwidgets is needed to build Browse3D, a bundled GUI application for viewing 3D files: it can be omitted if so desired. Add --with-osmesa to install OSMesa for headless CPU-only rendering (good for remote servers). Replace 4 with the actual number of hardware threads on your system, typically 2, 4, or 8.

The above step will install the necessary libraries by compiling them from source (if not apt-getable) and placing the result in $prefix. Carefully check for errors (warnings are generally ok). If there are errors, you probably need to explicitly install some third-party libraries/tools -- see the error messages -- and rerun the command. Make sure there are no errors in the output before proceeding further.

Installing the Thea library, plugins and bundled tools

Assuming there were no errors while installing the dependencies, execute the following commands:

cd "$basedir"
git clone --recursive
cd Thea/Code/Build
make -j4
make install    # add sudo if necessary

By default, CMake looks for the dependencies in the CMAKE_INSTALL_PREFIX directory. If for some reason the dependencies are located somewhere else, e.g. in $deps, you can point CMake to it by adding -DTHEA_DEPS_ROOT="$deps". The bundled tools are installed to $prefix/bin/Thea: add this to your executable search path (e.g. the system PATH variable) as needed. A quick way to check if everything has installed correctly is to run

$prefix/bin/Thea/Browse3D ../../Data/Models/teapot.obj

and see if a window pops up displaying a 3D teapot, or

$prefix/bin/Thea/RenderShape ../../Data/Models/teapot.obj teapot.png 800 600

to render the teapot to an image file.

To build with OSMesa instead of the system OpenGL driver, add -DWITH_OSMESA=true to the CMake line above. The RenderShape tool will then use OSMesa. To run some test scripts (several probably out of date), run make test after building. To omit building the tests altogether, pass -DWITH_TESTS=false to CMake. To change the build type (by default Release), set -DCMAKE_BUILD_TYPE=Debug|Release|RelWithDebInfo.


To generate HTML documentation for the API, run Doxygen in the Thea/Code/Documentation folder. Then, open html/index.html in a browser.

This is probably the best place to start looking at the toolkit.

Note that many convenience types, such as Vector3 and Matrix4, are typedefs (for Eigen::Matrix<Real, 3, 1, ...> and Eigen::Matrix<Real, 4, 4, ...> respectively) and don't show up in the Class Index. Some will show up in Namespaces --> Namespace Members --> Typedefs. For others, you will have to look at the source code. Documenting all of these properly is work-in-progress.)

Using the library

GCC/Clang-specific: You MUST compile with strict aliasing turned OFF. This is achieved with -fno-strict-aliasing. I also recommend -Wall -g2 -O2 (all Warnings, debuGgable binaries, Optimize for speed). -O2 messes up the debugging a bit so turn it off temporarily if you can't track down your bug.

The usual command line to link your program with the library is:

c++ -std=c++11 -Wall -g2 -O2 -fno-strict-aliasing \
    -I"$prefix/include" \
    <source-files> \
    -L"$prefix/lib" -lThea \
    -lboost_filesystem -lboost_system -lboost_thread \
    -lm \
    [-ldl] [-framework Carbon]

If you're using CMake for your own code, a convenient FindThea.cmake module in Thea/Code/Build/Common/CMake/Modules (or directly from allows you to do FIND_PACKAGE(Thea), including locating all the necessary dependencies.

Sample code

Here is a simple "Hello World" example:

#include <Thea/MatVec.hpp>

int main(int argc, char * argv[])
  using namespace Thea;

  Vector3 v(1.0, 2.0, 3.0);
  Matrix3 m = Math::rotationArc(Vector3(1, 0, 0), Vector3(0, 1, 0));

  // Automatically adds newline and synchronization to std::cout...
  THEA_CONSOLE << "Hello world! The product is " << toString(m * v);

For real-world samples, see the applications in the Thea/Code/Source/Tools folder.

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