Best way to update ROS_PACKAGE_PATH

#Assuming you have a package installed called ethzasl_ptam

# Update ROS_PACKAGE_PATH (if necessary)
export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:`pwd`/ethzasl_ptam

Configuring xsens_driver for XSENS IMU in ROS

Here I employ xsens MTI-G IMU which is orange in colour.

I am working in ROS FUERTE on ubuntu 12.04 using the xsens_driver package that ships in ethzasl_xsens_driver.

I tried to get all the relevant data from IMU namely
orientation
orientation covariance
angular velocity
angular velocity covariance
linear acceleration
linear acceleration covariance

Configuration steps
1. Attach IMU via USB
2. sudo chmod 777 /dev/ttyUSB0
3.  rosrun xsens_driver mtdevice.py --configure --output-mode=coapvs --output-settings=tqMAG

The above command should result in something like this

Configuring mode and settings  Ok

4. roslaunch xsens_driver xsens_driver.launch

5. rostopic echo /imu/data

Then it should display

header:
  seq: 166
  stamp:
    secs: 1396073832
    nsecs: 314651012
  frame_id: /imu
orientation:
  x: -0.00116935407277
  y: -0.0249380189925
  z: 0.306782633066
  w: 0.95145213604
orientation_covariance: [0.017453292519943295, 0.0, 0.0, 0.0, 0.017453292519943295, 0.0, 0.0, 0.0, 0.15707963267948966]
angular_velocity:
  x: 0.00783694628626
  y: -0.0136562986299
  z: 0.00587089639157
angular_velocity_covariance: [0.0004363323129985824, 0.0, 0.0, 0.0, 0.0004363323129985824, 0.0, 0.0, 0.0, 0.0004363323129985824]
linear_acceleration:
  x: 0.347801417112
  y: -0.202733114362
  z: 9.81818389893
linear_acceleration_covariance: [0.0004, 0.0, 0.0, 0.0, 0.0004, 0.0, 0.0, 0.0, 0.0004]
---

Good day!

XSENS diver from ethzasl_xsens_driver error on ubuntu 12.04

Error

WARN] [WallTime: 1362075228.016104] Cannot find value for parameter: ~device, assigning default: auto

[WARN] [WallTime: 1362075228.017062] Cannot find value for parameter: ~baudrate, assigning default: 0

[ERROR] [WallTime: 1362075228.018932] Fatal: could not find proper MT device.


SOLUTION


One has to give proper permissions to access the port, which can be done by

sudo chmod a+rw /dev/ttyUSB0

Good day!

Authentication Required for adding printer in Ubuntu

Solution:

Just trigger the application using

gksudo system-config-printer

and the problem is solved

Understanding 3D Rigid Body Transformation

A good tutorial on 3D rigid body transformation, Euler angles i.e. roll, pitch and yaw, the rotation matrix can be found in the link below.

Just traverse to before and next sections for better understanding :)

http://planning.cs.uiuc.edu/node102.html

http://www.cs.iastate.edu/~cs577/handouts/homogeneous-transform.pdf

Differentiation of norm

source  :  http://math.stackexchange.com/questions/291318/derivative-of-the-2-norm-of-a-multivariate-function

Suppose f:Rm→Rn. Decompose into f=(f1,…,fn). Each fi is a real-valued function, i.e., fi:Rm→R. Then

g(X)=∥f(X)∥2=∑i=1nfi(X)2−−−−−−−−−√.

Therefore,

∇g(X)=12(∑i=1nfi(X)2)−12(∑i=1n2fi(X)∇fi(X))=∑ni=1fi(X)∇fi(X)∥f(X)∥2.

This matches your answer.

If you want to write in terms of the Jacobian matrix of f instead of components fi, you can:

∇g(X)=Jf(X)Tf(X)∥f(X)∥2.