Use the GPU ORB Extractor

This tutorial shows how to use the GPU orb-extractor feature library API.

The GPU orb-extractor feature library offers thread-safe support for both single and multiple cameras.

This tutorial illustrates GPU orb-extractor feature library usage with OpenCV cv::Mat and cv::Keypoints. It explains using multiple CPU threads with multiple ORB extractor objects, as well as using a single orb-extractor feature object to handle multiple camera inputs.

The multithread feature provides more flexibility for Visual SLAM to call multiple objects of the orb-extractor feature library.

Prerequisites

Complete the Robot on Intel Getting Started Guide before continuing.

Tutorial

Note: This tutorial can be run both inside and outside a Docker image. It assumes that the liborb-lze-dev Deb package is installed and the user has copied the tutorial directory from /opt/intel/orb_lze/samples/ to a user-writable directory.

1. Prepare the environment:

   sudo apt install liborb-lze-dev libgflags-dev
   cp -r /opt/intel/orb_lze/samples/ ~/orb_lze_samples
   cd ~/orb_lze_samples/
   

2. main.cpp should be in the directory. View it on GitHub to read the comments for the code.

3. Build the code:

   mkdir build && cd build
   cmake ../
   make -j
   

4. Run the binary:

   ./feature_extract -h
   

   • Available command line arguments:

   Usage: ./feature_extract --images=<> --image_path=<> --threads=<>
   
     --images <integer>     : Number of images or number of cameras. Default value: 1
     --image_path <string>  : Path to input image files. Default value: image.jpg
     --threads <integer>    : Number of threads to run. Default value: 1
     --iterations <integer> : Number of iterations to run. Default value: 10
   

   • The following command runs four threads, each thread taking two camera image inputs:

   ./feature_extract --images=2 --threads=4
   

5. Expected results example:

   ./feature_extract --images=2 --threads=4
    iteration 10/10
    Thread:2: gpu host time=21.4233
    iteration 10/10
    Thread:1: gpu host time=21.133
    iteration 10/10
    Thread:4: gpu host time=20.9086
    iteration 10/10
    Thread:3: gpu host time=20.6155
   

   After execution, the input image displays keypoints as blue dots.

   

   Note: You can specify the number of images per thread and the number of threads to execute. You can process multiple image inputs within a single thread of the extract API, or process one or more image inputs using multiple threads with extract API calls.