libQEx – A Robust Quad Mesh Extractor

libQEx is an implementation of QEx [Ebke et al. 2013] distributed under GPLv3. Commercial licensing is available upon request.

If you make use of libQEx in your scientific work, please cite our paper. For your convenience, you can use the following bibtex snippet:

 author = {Ebke, Hans-Christian and Bommes, David and Campen, Marcel and Kobbelt, Leif},
 title = {{QE}x: Robust Quad Mesh Extraction},
 journal = {ACM Trans. Graph.},
 issue_date = {November 2013},
 volume = {32},
 number = {6},
 month = nov,
 year = {2013},
 issn = {0730-0301},
 pages = {168:1--168:10},
 articleno = {168},
 numpages = {10},
 url = {},
 doi = {10.1145/2508363.2508372},
 acmid = {2508372},
 publisher = {ACM},
 address = {New York, NY, USA},
 keywords = {integer-grid maps, quad extraction, quad meshing},

What is QEx?

QEx (pronounced \'kyü-eks\) is a method for robust quad mesh extraction from Integer-Grid Maps with imperfections. (Imperfect) Integer-Grid Maps are what is generated by most state-of-the-art quad meshing methods such as QuadCover [Kälberer et al. 2007] or our own Mixed-Integer Quadrangulation [Bommes et al. 2009].

Quad extraction is often believed to be a trivial matter but quite the opposite is true: numerous special cases, ambiguities induced by numerical inaccuracies and limited solver precision, as well as imperfections in the maps produced by most methods (unless costly countermeasures are taken) pose significant challenges to the quad extractor.

Read our paper if you want to find out why quad extraction is complicated and how we tackle it or skip ahead and download the source code if you don't care about the details and just need results.


You can download the latest version of libQEx over at GitHub. Build and usage instructions, as well as a bunch of unittests and demos are included.


libQEx is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. See

If you make use of libQEx in scientific work we kindly ask you to cite our paper. (You can use the bibtex snippet above.)

Commercial licensing under negotiable terms is available upon request. Please send an email to if you are interested.


If you encounter an issue/bug/segfault you are more than welcome to report the issue on libQEx' GitHub page.


Bommes, D., Zimmer, H., and Kobbelt, L. 2009. Mixed-integer quadrangulation. In Proc. SIGGRAPH 2009.

Ebke, H.-C., Bommes, D., Campen, M., and Kobbelt, L. 2013. QEx: Robust Quad Mesh Extraction. ACM Trans. Graph., 32(6):168:1–168:10, November 2013.

Kälberer, F., Nieser, M., and Polthier , K. 2007. Quadcover - surface parameterization using branched coverings. Computer Graphics Forum 26, 3, 375–384.

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