===== Data logging with mongodb =====
There is a tool for loggin data into mongodb for later processing. The data is fetched from selected topics or all topics when running a ROS process. The logging tool is from the package **mongodb_log**.

==== Installing the logger ====
Using a properly set up ros environment (rosws set command working), get the patched sources using instructions below;

* Install **roslua** as shown below
  rosws set roslua --git https://github.com/timn/roslua.git
  rosws update roslua
  # source bashrc/zshrc
  roscd roslua
  # install the ubuntu dependencies specified on the rosdep.yaml file in the roslua package
  rosmake roslua
  
* Install **mongodb** package from ROS as shown below
  rosws set warehouse-hg --hg http://kforge.ros.org/warehousewg/warehouse-hg
  rosws update warehouse-hg
  # source bashrc/zshrc
  # install dependencies (scons and v8) as given below
  sudo apt-get install scons
  sudo apt-get install libv8-dev
  rosmake mongodb
  
* Install the mongodb logger package;
  rosws set mongodb_log --git https://github.com/makokal/ros-mongodb_log.git
  rosws update
  # source bashrc/zshrc
  # Install the logger system dependencies (given for ubuntu)
  sudo apt-get install python-pymongo python-pyrrd mongodb
  rosmake mongodb_log
==== Logging with mongodb_log ====
Run the logger node
  rosrun mongodb_log mongodb_log -a # record all topics or specify required ones
  # use the tool mongodb_rdd to check

==== Querying the log database ====
The data from the database can be retrieved using any of the mongo clients APIs. For cram, the cl-mongo client is recommended but there are clients for any popular language around like Python, C++ etc. For mython, the pymongo client has already been wrapped in ROS here [[http://ros.org/wiki/pymongo|http://ros.org/wiki/pymongo]] and we have wrapped the common lisp version as well. It can be installed using;

  rosws set ros_cl_mongo --git https://github.com/makokal/ros_cl_mongo
  rosws update ros_cl_mongo
  # source bashrc
  rosmake ros_cl_mongo # may take some time
  
The use it from the standard emacs REPL environment as follows;
  rosrun roslisp_repl repl
  # Now load the ros-cl-mongo package and interact with the database using it
  
Further usage instructions on cl-mongo are available at [[https://github.com/fons/cl-mongo|https://github.com/fons/cl-mongo]]
==== Locating the Database ====
The database is by default located in ''/var/lib/mongodb/'' where you are able to notice the databases named ``roslog.1`` etc. The mongo client knows about this path so starting mongo from any resonable location will still access this databases. Of course this path can be changed using the ''--dbpath'' flag on mongo to change where to read or write. In summary the database features of importance are;
  * Hostname : localhost (by default)
  * Port: 27017 (default)
  * Locatation: ''/var/lib/mongodb/''


==== Examples of usage ====
We have compiled simple example of logging with this tool and querying the data using either lisp or python. The examples are in the links below:

* [[:logging_tutlesim|Logging turtlesim data]]