difference between opt/ros/jade and catkin_ws

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Hi everyone,

as working with ROS I am getting a bit confused about the filesystem used.

First: Is it correct, to clone a, what I believe is a "stack" to my catkin_ws/src and then running the mandatory rosbuild in catkin_ws main folder and after that installing the stack and then adding all dependencies? I am not sure if you properly do this steps with a ros pack instead a whole stack.

Second: Is it necessary to let the packages I want to use in the src folder after building? I think they are build everytime when I run rosbuild when adding new packages I want to work with. I am sure, that when I edit the code in the packages, I need to build them again, but without changing anything in the code this step would be redundant and timewasting.

third: What exacly is the difference between the opt/ros/jade directory and the catkin_ws? I can see, that in the opt directory many libraries were already installed with my ros installation. Can I use and edit them and what do I need to pay attention to? The catkin_ws is much more transparent for me.

fourth: I want to use a special package or stack (I cant quite classify what it is). mainly you could call it a library. its called "OctoMap", here is the link: https://github.com/OctoMap . Apperently a version of OctoMap was installed, when I installed ROS-Jade. I want the newest version of the Library. What to do to update it?

As you can see, in the github repository lay some different files. I am a bit confused, which one I can take for working with in ROS, as explained here ( http://wiki.ros.org/octomap ), that the only thing I'd need to do to use OctoMap would be "sudo apt-get install ros-fuerte-octomap" (in my case switch fuerte with jade I suppose).

Thanks for reading my questions, I am thankful for every answer.

Greets, Che

Edit: I have build the package with rosbuild. I cant seem to understand, which packages in my src folder are influenced by rosbuild and when I should use catkin_make? I read in http://wiki.ros.org/catkin_or_rosbuild that catkin_make is better used when foreign code is being used, as I do. Installing instructions in some other packages referred to rosbuild though.

Is it possible to combine those two commands in different packages?