Introduction

Visualization of orientation of any IMU with the help of a rotating cube as per quaternions or Euler angles (strictly speaking, the Tait Bryan Angles received over either the serial port or WiFi using OpenGL in Python. The MPU-9250 (has on-board accelerometer, magnetometer and gyroscope) has been used with Arduino for the demo below:

This is an easy to understand Python implementation of the often-used ‘MPU Teapot’ processing code (an example here) for visualizing an IMU, but not specific to any particular IMU (like the MPU6060 in the case of ‘MPU Teapot’). Note that this project does not do the sensor fusion of each sensor in the IMU to obtain the orientation (for the demo in the above gif, a Madgwick or Mahony filter was used from here to obtain the orientation). It is assumed that the user already has obtained the orientation in the form of either the yaw-pitch-roll angles or quaternions and wishes to visualize this real-time on-screen for debugging etc.

Requirements:

• pygame and PyOpenGL are used for graphics
• PySerial is used to get data from serial port
• simple python built-in UDP sockets are used to get data from WiFi.

Usage

Most of the code is self-explanatory. However some modifications might be required as per different use cases:

• Set useSerial to True if receiving data over serial and False if receiving data over wifi.
• Set serial port by changing the variable ser, if using serial for data transmission.
• Set udp port by changing the variable UDP_PORT, if using wifi for data transmission.
• Set useQuat to True if receiving quaternions over serial or WiFi and False if receiving Euler angles.
• If receiving quaternions over serial or wifi, the declination at the particular location should to be updated in quat_to_ypr(q) function to get correct yaw angles printed on screen. (The cube rotation is not dependent on this and will still work fine otherwise)

String passed over Serial or Wifi

To use this module, the data received over serial or udp port should be in the format specified below:

• First quaternion value should be between two w s
• Second quaternion value should be between two a s
• Third quaternion value should be between two b s
• Fourth quaternion value should be between two c s
• Yaw angle should be betweem two y s
• Pitch angle should be between two p s
• Roll angles should be between two r s

Either quaternion or Euler angles or even both can be received over the serial or udp port. If both are received, the useQuat variable defines which one is used to rotate the cube. So for example, all of the following are valid formats for the data received over the serial or udp port:

# Both quaternions and Euler angles
w0.09wa-0.12ab-0.09bc0.98cy168.8099yp12.7914pr-11.8401r

# Quaternions only
w0.09wa-0.12ab-0.09bc0.98c

# Euler angles only
y168.8099yp12.7914pr-11.8401r

Each of these must be on separate lines (or should have a ‘\n’ at the end of the string). Other data may also be passed over Serial or Wifi, provided that none of the characters w, a, b, c, y, p, r are passed (for example, somethingw0.09wa-0.12ab-0.09bc0.98cy168.8099yp12.7914pr-11.8401rsomethingelse is valid but somedataw0.09wa-0.12ab-0.09bc0.98cy168.8099yp12.7914pr-11.8401ranotherstring is not since it has the characters a and r)

Todos

• [x] Receive data over WiFi instead of serial. - **Done!**
• [ ] Add a nice argparse interface instead of requiring the user to change variables in the script. Include example usage in docstring (a la tldr or bro)
• [ ] Add some keyboard support, eg. pausing / resuming the visualization with spacebar etc
• [ ] Add optional support for x, y, z too. Also, multiple simultaneous viewports (eg. to compare with ground truth from MoCap)
• [ ] Read from text file instead of serial or UDP
• [ ] Other data collection methods: bluetooth?
• [ ] Write tests, docstrings etc