This is a combination of source codes of OPQ and Inverted MultiIndex. In our impementation, we use the inverted multi-indexing technique to perform non-exhaustive search for OPQ. The original code of OPQ is implemented by MATLAB, which is used to transform the data vectors and query vectors for finding the minimal quantization distortion. For the search efficiency, we apply the inverted multi-indexing technique implemented by C++ to perform non-exhaustive search.

##Prerequisites

• Yael and VLFeat libraries (for the Matlab code)
• A modern compiler that supports C++11 (e.g., gcc 4.7 and above)
• Matlab
• CMake (version 2.6 or over)
• The boost library (dev version) installed.
• IntelMKL

##Compile (OPQ/src)

To compile, go to src directory and type

./build_release.sh

Note that the local directory of Boost and IntelMKL should be provided (CMakeLists.txt).

##Index (OPQ/Transform_Data and OPQ/script)

To get OPQ indexing, one should first enter the Transform_Data folder and run

main.m 

in the Matlab to get the transformed data vectors and query vectors, coarse vocabularies and fine vocabularies. Note that the directories of Yael and vlfeat libraries should be given in the main.m file.

Then go to OPQ/script directory and run

./indexer.sh 

to build the OPQ index.

##Search (OPQ/script)

./search.sh

Note that, in our experiment paper, we tune the c value of OPQ search (i.e., size of neighbors to be visited) to achieve the trade-off between search speed and search quality (recall). The search performance (time and recall) results are kept in the OPQ/results directory.