Optitrack on Raspberry Pi

Using Optitrack and thin NatNet client using C++

Back to ASTA motion capture

Use

The PacketClient described here is a "Direct Depacketization" code for NatNet and is not using the NatNat SDK, and thus have to be updated if the data structure used in NatNet is changed.

The Git repository is maintained, so you should keep the modifications to this file small, so that future updates are easily integrated.

Install original sample version

Optional install, you may want to use the version adapted to Asta, see next section.

Get client from https://github.com/b4be1/packet-client-linux e.g. directly to the raspberry:

git clone https://github.com/b4be1/packet-client-linux.git
cd packet-client-linux
mkdir build
cd build
cmake ..
make

Filelist:

NatNetClient.py    - python client
requirements.txt   - almost empty
CMakeLists.txt     - cmake instructions
PacketClient.cpp   - source code
README.md          - how to use/compile

The CMakeLists.txt is rather short (only the pthread library is needed):

cmake_minimum_required(VERSION 2.8)
project(PacketClient)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -Wall")
add_executable(PacketClient PacketClient.cpp)
target_link_libraries(PacketClient pthread)

Install ASTA version

The Asta version is adapted to the Asta Optitrack version and includes data extraction for solid bodies only.

This is not ROS based. If you use ROS, then you should use the ROS package instead.

Get the source code

Install prerequisites.

sudo apt install subversion cmake

Get from repository

cd
svn co svn://repos.gbar.dtu.dk/jcan/asta optiAsta
cd optiAsta
mkdir build
cd build
cmake ..
make

It should produce an executable called optiAsta, run by:

~/optiAsta/build/optiAsta

This version includes 2 classes

class URigid
{
public:
 int ID;
 float pos[3];  // position in m in the Opritrack coordinates
 float rotq[4]; // orientation - quartonions - I think
 float posErr;
 bool valid;    // true, if visible
 void printRigid(); // print on console
};

and a class to hold all rigid bodies

class UOptitrack
{
protected:
 // positions
 static const int MAX_MARKERS = 30;
 URigid * markers[MAX_MARKERS] = {nullptr};
 int markersCnt = 0;
 double timestamp;
public:
 void print();
 URigid * findMarker(int id);
public:
 // major NatNet unpack, modified version of the one in PacketClient.cpp
 void unpack(char * pData);
};

One instance of UOptitrack is created in the main.cpp file. Use the 'findMarker(int ID)' to get a pointer to a URigid with the position of that rigid body.

The function 'unpack(...)' is called in a thread every time there is a new frame.

Raspberry setup

On the Raspberry Pi set the wireless network to access the dedicated Optitrack network

Modify the /etc/wpa_supplicant/wpa_supplicant.conf by adding the network groups. The 5Ghz SSID has in this case higher priority (higher number).

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
ctrl_interface_group=0
update_config=1
country=DK

network={
       ssid="asta_optitrack"
       psk="asta2020"
       priority=1
}

network={
       ssid="asta_optitrack_5G"
       psk="asta2020"
       priority=2
}

Restart the network by reboot or just restart the network:

sudo /etc/init.d/networking restart

Optitrack setup

In

• EDIT mode (bottom of window left)

In 'View' and 'Data streaming pane'

• select 'local interface' to the IP address of the server (192.168.1.129) and
• deselect other streaming services (VRPN and Trackd) if not used by others

In 'View' and 'Assets Pane'

• check the relevant rigid bodies

Then

• go live (bottom of window left)

and assuming there is at least one rigid body defined and visible, streaming should commence.

Modify the original source

The NatNet version should be changed - it is hard-coded in source file.

 cd ~/packet-client-linux
 nano PacketClient.cpp

A bit down change the NatNetVersion to 3.1 (to fit Motive version 2.2)

// Versioning
int NatNetVersion[4] = {3, 1, 0, 0};
int ServerVersion[4] = {0, 0, 0, 0};

The multicast address is "239.255.42.99" and should not be changed.

Compile the client

Compile

cd ~/packet-client-linux/build
make

Run the client

cd ~/packet-client-linux/build
./PacketClient DESKTOP-OVLVRUD.local 192.168.1.136

where DESKTOP-OVLVRUD is the hostname of the Optitrack server (in ASTA) and 192.168.1.136 is the IP of the raspberry pi in this case.

Data in client

The client should then print package data on the console. The frame data packet looks like this:

Begin Packet
-------
Message ID : 7
Byte count : 220
Frame # : 285290
Marker Set Count : 0
Rigid Body Count : 1
ID : 20
pos: [0.73,0.57,-0.15]
ori: [-0.01,-0.00,1.00,0.02]
Mean marker error: 0.00
Tracking Valid: True
Skeleton Count : 0
Labeled Marker Count : 4
ID  : [MarkerID: 1] [ModelID: 20]
pos : [0.72,0.50,-0.15]
size: [0.01]
err:  [0.00]
ID  : [MarkerID: 2] [ModelID: 20]
pos : [0.78,0.53,-0.14]
size: [0.01]
err:  [0.00]
ID  : [MarkerID: 3] [ModelID: 20]
pos : [0.74,0.62,-0.15]
size: [0.01]
err:  [0.00]
ID  : [MarkerID: 4] [ModelID: 20]
pos : [0.66,0.64,-0.15]
size: [0.01]
err:  [0.00]
Timestamp : 2377.417
Mid-exposure timestamp : 12335057189261
Camera data received timestamp : 12335057223494
Transmit timestamp : 12335057235053
End Packet

The data is thus available in the client and should be integrated into the intended application (by further source code editing).