PCL Developers blog

Raymond Lo

email:raymondlo84 (at) gmail (dot) com
project:Real-time 3D Applications based on PCL, Microsoft Kinect, OpenNI, and Tegra 3

Recent status updates

Preview: Finger Tracking + Android 4.0 + Tegra 3 + Kinect + OpenNI + OpenCV
Monday, June 11, 2012

In the coming tutorial, we will show you how to implement the ‘well-known’ finger tracking algorithm on Kinect + Android + OpenNI + Tegra3 + OpenCV. The algorithm is indeed very simple and computationally efficient. We can achieve real-time performance easily on Tegra 3!

We will be using the range camera (depth map) to create a contour of our hand. Then, we will perform a simple polynomial approximate on the contour, and extract the convex hull (the peaks) as our finger tips. All of these operations can happen in real-time on the Tegra 3 @ 25fps! That’s pretty impressive.

The requirements are as follows:

1. Tegra 3 or Tegra 2 Android device.
2. Microsoft Kinect or Asus Xtion (not tested)
3. NVIDIA NDK + OpenNI binary (see my previous tutorials)
4. OpenCV binary (will be provided below)
5. and 10 mins of your time :)

First of all, the method provided here are simplified for real-time usage, and we can get better results if we have a better way of extracting the hand location and filtering the depth map (See Limitation section at the end). Right now, we are thresholding on a range, i.e., we assume that the hand of a person will be positioned closer to the range camera.

Depth Segmentation and Contour Extraction
Bounding Boxes
Simple Gesture recognition - finger and grasp detection
Tegra 3 Tablet + Microsoft Kinect + My custom 12V battery
Hand Tracking with 3D PointCloud Data rendering in real-time on Tegra3.
Source code:
PCL svn repository (in about two weeks)
What’s next?
Using the OpenNI hand tracking and create several interfaces. Right now we have the point cloud data visualization on Android controlled by the Kinect at 15-20fps (with about 2 million dots).
OpenNI + Android FAQ
Thursday, May 24, 2012

Recently, we have received several emails about the OpenNI and Android development. Here we will address some of the most frequently asked questions and some of the future directions about this project.


Q: What tablet have we used?

Ans: We’ve used the Tegra 2 and Tegra 3 Development Board provided by NVIDIA. http://developer.nvidia.com/tegra-development-kits. I can safely assume that as long as your Tablet is as capable as Tegra 2, the OpenNI library shall be able to grab the depth map image and color images at 640*480 resolution at full speed. However, I have experienced some hiccups with the OpenNI drivers, especially the color image gets corrupted sometimes.

Q: What are the minimum OS requirements?

Ans: We’ve tested everything from Android 3.0 to Android 4.x. However, I noticed that I have got better performance on Android 3.x OS? That’s something I’m currently working on.

Q: How could I know if my tablet work with the Kinect?

Ans: Try dmesg under ‘adb shell’. You should be able to see the Microsoft Kinect is recognized as a USB hub with camera, motor, and audio devices. If you cannot see any USB devices attached, I believe we need to look into that further.

Q: I’ve trouble getting the ‘multitouch’ sample code compiled?

Ans: We notice that the NDK package from NVIDIA http://developer.nvidia.com/tegra-resources. There are some dependencies that become missing in the latest SDK. I’m current working on this (basically rewriting part of the code to be conformed with the “Android Application Lifecycle in Practice: A Developer’s Guide”. LINK: http://developer.nvidia.com/sites/default/files/akamai/mobile/docs/android_lifecycle_app_note.pdf . Please check this blog again in the future for a more self-contained package.

Q: I’m getting errors when compiling the OpenNI library. What should I do?

Ans: We would highly recommend others to use the binary (as provided in the last tutorial) for the first time. I will provide a sample script for recompiling in the future.

Q: How do I push the .so libraries to the device?

Ans: Please read the push_lib.sh file in the package. We’ve provided a few comments on how to remount the /system directory for read-write.

Q: Who’s raymondlo84?

Ans: I’m a Ph.D student studying ECE at UofT. I’m currently working with PCL and NVIDIA’s summer code program and free feel to let us know what you think about the Android project.

Thank you.

Quick Tutorial: A simple C++ OpenNIWrapper for using OpenNI on Android Devices
Monday, May 14, 2012
Important: In this tutorial, we assume that you have already installed the OpenNI shared libraries as previously discussed to your device and so. If you haven’t done so, please follow our previous post and adb push the binary libraries to the proper location Additionally, you are required to perform
mount -o devmode=0666 -t usbfs none /proc/bus/usb

everytime after you rebooted your device. The example code provided below has been tested on the NVIDIA Tegra 3 dev board and Microsoft Kinect only. If you would like to use Xtion or other range sensors, you may need to compile the drivers, and make appropriate updates to the modules.xml file. For more information, see our previous post.

To get started, we will first introduce the simple c++ wrapper we have written for handling the OpenNI calls. In this example, we will be only handling the image buffers, the color image buffer (24 bits RGB image) and the depth image buffer (16 bits single channel). I believe we can also record audio with the Kinect (?), but we have not verify that yet. Here we have the header files from our OpenniWrapper.h.

Sample Usage

To get started, you can download the header and cpp file here
http://openvidia.svn.sourceforge.net/viewvc/openvidia/tegra_kinect/jni/OpenniWrapper.cpp?view=log http://openvidia.svn.sourceforge.net/viewvc/openvidia/tegra_kinect/jni/OpenniWrapper.h?view=log

Our wrapper consists of three main function calls, start(), release(), and WaitAndUpdate(). By default, the openni wrapper will initialize the depth map and rgb image and runs in a separate thread (i.e., non-blocking) after the start(). To obtain the depth map or rgb images, we simply call WaitAndUpdate() (blocking call) and then provide a pointer which stores our depth and rgb image. The OpenniWrapper does not provide any memory allocation and it is our responsibility to handle the malloc and free.

#include “OpenniWrapper.h”
OpenniWrapper *openni_driver;
int main(){

openni_driver = new OpenniWrapper();


//initialize the driver
//something is wrong. see log files
return 1;

int width = openni_driver->getWidth();
int height = openni_driver->getHeight();
unsigned char *rgb_buffer = (unsigned char*)malloc(width*height*3*sizeof(unsigned char));
unsigned short *depth_buffer = (unsigned short*)malloc(width*height*sizeof(unsigned short));

WaitAndUpdate(); //blocking call
process_buffers(); //can be multithreaded

//release the resources
To compile the source with the OpenNI libraries, we need to include the OpenNI headers and the shared lib paths to the Android.mk file. Particularly, I have added


LOCAL_C_INCLUDES += openni_kinect_include/include

You can find the openni_kinect_include/include directory from the SVN respository below. Or you can simply create that directory by copying the headers from the OpenNI source directly.

CPU usage and FPS:
12539 2 60% R 14 532164K 65048K fg app_39 com.nvidia.devtech.multi
I/Render Loop:(12539): Display loop 0.014692 (s) per frame –> over 60fps for rendering, the capture loop is threaded.

OpenNI Binary (Kinect Only)


Sample Source Code


Porting OpenNI to Android 4.0 + Microsoft Kinect + Tegra 2 + Sample Code
Wednesday, April 25, 2012

In this tutorial, we will show you how to compile OpenNI shared libraries and install them on your Android devices. Also, we will show you how extract the depth map information from the Microsoft Kinect with the SensorKinect driver (note: the OpenNI framework does not come with any drivers! Instead it dynamically loads the modules in runtime!). Before we start, I assume that we have already installed the following packages. I have tested this setup on my Mac OSX 10.6.8, and I believe Linux users shall not have any problems replicating these. Any Windows users? :)

System Requirements:

First, let’s get the OpenNI sources from the Git repository

cd ~/NVPACK/android-ndk-r7b/sources
cd OpenNI/Platform/Android/jni

If everything goes well, we will see the following files in this directory.

ls ~/NVPACK/android-ndk-r7b/sources/OpenNI/Platform/Android/libs/armeabi-v7a/
Sample-SimpleRead libOpenNI.so libnimRecorder.so niReg
Sample-SimpleSkeleton libnimCodecs.so libusb.so
libOpenNI.jni.so libnimMockNodes.so niLicense

Now, we will compile the SensorKinect Driver.

export NDK_MODULE_PATH=$HOME/NVPACK/android-ndk-r7b/sources/OpenNI/Platform/Android/jni
mkdir ~/NVPACK/openni
cd ~/NVPACK/openni
cd SensorKinect
git checkout faf4994fceba82e6fbd3dad16f79e4399be0c184
cd Platform/Android/jni

Again, if everything goes well, the ndk-build will create another set of .so shared libraries files in this directory

ls ~/NVPACK/openni/SensorKinect/Platform/Android/libs/armeabi-v7a
libOpenNI.so libXnDDK.so libXnDeviceSensorV2.so libusb.so
libXnCore.so libXnDeviceFile.so libXnFormats.so

Finally, we are ready to push these libraries on the Android device. One problem is the /system directory is read-only. Therefore, we have to remount this directory first by

adb shell
mount -o remount rw /system
mkdir /data/ni

Then, we push the packages to the device with these commands (these are our previously compiled .so files!)

adb push libOpenNI.so /system/lib
adb push libOpenNI.jni.so /system/lib
adb push libXnCore.so /system/lib
adb push libXnDDK.so /system/lib
adb push libXnDeviceFile.so /system/lib
adb push libXnDeviceSensorV2.so /system/lib
adb push libXnFormats.so /system/lib
adb push libusb.so /system/lib
adb push libnimCodecs.so /system/lib
adb push libnimRecorder.so /system/lib
adb push libnimMockNodes.so /system/lib

In runtime, the OpenNI framework will look for these shared libraries. To inform the OpenNI which modules to load, we need to commit this .xml file to this directory. It is very very important that all these files are put in the properly directories!

adb push data/in/modules.xml /data/ni

Here is example modules.xml file we have used.

<Module path=”/system/lib/libnimMockNodes.so” />
<Module path=”/system/lib/libnimCodecs.so” />
<Module path=”/system/lib/libnimRecorder.so” />
<Module path=”/system/lib/libXnDeviceSensorV2.so” configDir=”/data/ni/” />
<Module path=”/system/lib/libXnDeviceFile.so” configDir=”/data/ni/” />

As we can see from the modules.xml, the XnDeviceSensorV2 will look for

vim ~/NVPACK/openni/SensorKinect/Data/GlobalDefaultsKinect.ini
#and we will need to set the flag UsbInterface to 1.
#assume you are in that directory
adb push GlobalDefaultsKinect.ini /data/ni/

Lastly, we will copy the SamplesConfig.xml to the /data/ni/ directory as well. You can find this file from the sample code in OpenNI or from our svn repository.

adb push SampleConfig.xml /data/ni/

That’s it! Now, we have the latest OpenNI + Kinect Driver compiled and install on your Android! In the coming up tutorial, I explain how we can use these drivers with NDK with sample codes! and more tricks are coming up! (e.g., mount -o devmode=0666 -t usbfs none /proc/bus/usb) !!

If you would like to check if the modules are installed successfully, you can run trying niReg on your Android device.

adb push niReg /system/bin

and run

root@android:/ # niReg -l (under adb shell)

and you should see something similar to...

. . .
/system/lib/libXnDeviceSensorV2.so (compiled with OpenNI
Device: PrimeSense/SensorV2/
Depth: PrimeSense/SensorV2/
Image: PrimeSense/SensorV2/
IR: PrimeSense/SensorV2/
Audio: PrimeSense/SensorV2/
. . .

Hirotaka Niisato (http://www.hirotakaster.com/) has also provided excellent tutorials on how to compile OpenNI on Android! I would like to thank him for providing some of the basic scripts for compiling the libraries! ;). However, I’ve trouble running the sample code he has provided. Instead, I have ported the Sample-NiSimpleRead to run on Android instead. ;) Stay tuned!

Here is the complete script we have used: copy and paste these and that will get you started.

#adb shell
#mkdir /data/ni
#mount -o remount rw /system
#mount -o devmode=0666 -t usbfs none /proc/bus/usb

adb push system/lib/libOpenNI.so /system/lib
adb push system/lib/libOpenNI.jni.so /system/lib
adb push system/lib/libXnCore.so /system/lib
adb push system/lib/libXnDDK.so /system/lib
adb push system/lib/libXnDeviceFile.so /system/lib
adb push system/lib/libXnDeviceSensorV2.so /system/lib
adb push system/lib/libXnFormats.so /system/lib
adb push system/lib/libusb.so /system/lib
adb push system/lib/libnimCodecs.so /system/lib
adb push system/lib/libnimRecorder.so /system/lib
adb push system/lib/libnimMockNodes.so /system/lib
adb push modules.xml /data/ni/
adb push GlobalDefaultsKinect.ini /data/ni/
adb push SamplesConfig.xml /data/ni/