News about OpenSynther

May 9th, 2011 by Henri Leave a reply »

I’ve worked a lot on OpenSynther lately: OpenSynther is the name of my structure-from-motion solution. This new version is a major rewrite of the previous version which was using Surf with both GPU and multi-core CPU matching. The new version is using SiftGPU and Flann to achieve linear matching complexity of unstructured input as described in Samantha paper. You can find more information about OpenSynther features on it dedicated page (including source code).

OpenSynther has been designed as a library (OpenSyntherLib) which has already proven to be useful for several programs written by myself:

  • OpenSynther: work in progress… used by my augmented reality demo
  • PhotoSynth2CMVS: this allow to use CMVS with PhotoSynthToolkit
  • BundlerMatcher: this is the matching solution used by SFMToolkit

Outdoor augmented reality demo using OpenSynther

I’ve improved my first attempt of outdoor augmented reality: I’m now relying on PhotoSynth capability of creating a point cloud of the scene instead of Bundler. Then I’m doing some processing with OpenSynther and here is what what you get:

You can also take a look at the 3 others youtube videos showing this tracking in action around this church: MVI_6380.avi, MVI_6381.avi, MVI_6382.avi.


This is not ready yet, I still have some stuff to fix before releasing it. But I’m already producing a valid “bundle.out” file compatible with CMVS processing from PhotoSynth. I’ve processed the V3D dataset with PhotoSynth2CMVS and sent the bundle.out file to Olafur Haraldsson who has managed to create the corresponding 36 million vertices point cloud using CMVS and PMVS2:

The V3D dataset was created by Christopher Zach.


The new unstructured linear matching is really fast as you can see on the above chart compared to PhotoSynth. But the quality of the generated point cloud is not as good as PhotoSynth.

This benchmark was computed on a Core i7 with an Nvidia 470 GTX. I’ve also compared the quality of the matching methods implemented in OpenSynther (linear VS quadratic). I’ve used Bundler as a comparator with a dataset of 245 pictures:

Linear Quadratic
Nb pictures registered 193 243
Time spent to register 193 pictures 33min 1h43min

On the one hand, both the matching and the bundle adjustment are faster with linear matching but on the other hand, having only 193 out of 245 pictures registered is not acceptable. I have some idea on how to improve the linear matching pictures registering ratio but this is not implemented yet (this is why PhotoSynth2CMVS is not released for now).


I’ve been playing with LDAHash last week and I’d like to support this in OpenSynther to improve matching speed and accuracy. It would also help to reduce the memory used by OpenSynther (by a factor 16: 128 floats -> 256bits per feature). I’m also wondering if the Cuda knn implementation could speed-up the matching (if applicable)? I ‘d also like to restore the previous Surf version of OpenSynther which was really fun to implement. Adding a sequential bundle adjustment (as in bundler) would be really interesting too…


I’ve made some modifications to my blog: switched to WordPress 3.x, activated page caching, added social sharing buttons and added my LinkedIn account next to the donate button…



  1. rouli says:

    Help me to understand – what you do here is augmenting a video using a photosynth model but not in real time, right? that is, you have pre-recorded video and it takes you a few good minutes to match it with the model?

  2. Henri says:

    @rouli: You’re right: this video was produced offline. But my system can run at 20fps (without my current bad pose estimation), you can take a look at the timings on my previous post about this proof-of-concept. You don’t need to use this solution for every frame anyway: almost all AR solution are split in two parts: detection and tracking. So you can use my solution for detection and GPU-KLT for tracking and you’ll get an outdoor solution working in real-time.

  3. Michael D says:

    This stuff looks great! Henri, I am very impressed.

  4. Jason says:

    I keep trying to build opensynther in vs2010 and I keep getting lnk1120 and lnk2001 with gflags.lib and glob.lib. Any help would be appreciated. Thanks

  5. Henri says:

    @Jason: I need more information to be able to help you. You can contact me by email. Are you compiling in x64 or Win32? Because the version of libmv packaged with OpenSynther is a x64 only SDK (so you’ll need to compile libmv by yourself if you need a Win32 version). FYI I think that the gflags.lib is a google lib used by libmv.

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