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I have the following dependencies in my package.xml

<buildtool_depend>catkin</buildtool_depend>

<build_depend>message_filters</build_depend>
<build_depend>rosbag</build_depend>
<build_depend>rospy</build_depend>
<build_depend>tf</build_depend>

<build_export_depend>message_filters</build_export_depend>
<build_export_depend>rosbag</build_export_depend>
<build_export_depend>rospy</build_export_depend>
<build_export_depend>tf</build_export_depend>

<exec_depend>message_filters</exec_depend>
<exec_depend>rosbag</exec_depend>
<exec_depend>rospy</exec_depend>
<exec_depend>tf</exec_depend>

<exec_depend>python-h5py</exec_depend>
<exec_depend>python-opencv</exec_depend>
<exec_depend>python-pandas</exec_depend>
<exec_depend>python-tqdm</exec_depend>

I have done rosdep install my_package and catkin build inside my workspace (and I got no error). However, whenever I try to do pip list or to import any of the Python dependencies I specified above, such as Pandas or OpenCV, I get an ImportError or I don't see them in the list. I want to use those Python dependencies in my scripts or source files inside my_package.

If the correct way of specifying Python dependencies is by specifying them in <exec_depend> (see e.g. http://docs.ros.org/lunar/api/catkin/html/howto/format2/python_module_dependencies.html)), then why can't I see pandas when doing pip list?

I did not add anything. filters[topics.index(topic)].signalMessage(msg) was there since the beginning. @gvdhoorn How com

I did not add anything. filters[topics.index(topic)].signalMessage(msg) was there since the beginning.

Does rospy.init_node need to be called everytime? I developed two ROS packages and, until very recently, 1-2 days ago, I

Does rospy.init_node need to be called everytime? I developed two ROS packages and, until very recently, 1-2 days ago, I

Does rospy.init_node need to be called everytime? I developed two ROS packages and, until very recently, 1-2 days ago, I

Does rospy.init_node need to be called everytime? I developed two ROS packages and, until very recently, 1-2 days ago, I

Does rospy.init_node need to be called everytime? I developed several ROS packages and, until very recently, 1-2 days ag

rosdep can be used to install ROS packages or system dependencies (i.e. everything which is not a ROS package). There are dependencies used by certain ROS packages (but not only), which can be installed using apt or pip. For example, rosdep itself can be installed using apt or pip.The tool rqt_plot can be installed using rosdep or using e.g. sudo apt-get install ros-indigo-rqt (as stated here: http://wiki.ros.org/rqt_plot ).

Why are there multiple tools to manage and install dependencies (for our ROS packages)? Why are there multiple ways to install ROS packages? When should I use rosdep and when should I use apt or pip?

We can have a look at the documentation, but I have always to have a look at the documentation, that's a little bit annoying! If I had only one way of managing dependencies, I would not have to always look at the documentation.

I have read the initial part of the article http://wiki.ros.org/catkin/workspaces , but I am still not having an intuitive understanding of why we need the devel, build and install spaces. I can infer that the devel space may contain mainly packages useful while developing (i.e. while editing the files in the src directory, i.e. the source files, but then what's the purpose of the src space?). What’s the difference between the devel, build and install spaces?

I also have a few specific questions regarding the documentation I am linking you to above.

Regarding the build space, it states

The build space is where CMake is invoked to build the catkin packages in the source space.

Given that I am not very familiar with make and cmake, what does it mean "to build a package" in the context of catkin?

Then, it states regarding the devel space

The development space (or devel space) is where built targets are placed prior to being installed.

Again, given my ignorance regarding make and cmake, first of all, what is a target in the context of catkin, workspaces and ROS packages? What is a built target? Why do we need to place built targets here before installing them? How is building a package different from installing? I understood we are building packages, but what are we installing? When do we need to install after building (which I associate more to compiling and linking source files)? When don't we need to install?

Why are the folders devel, src, build and install called spaces?

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How to place a camera on top of the robot such that it covers a specific area around the robot? I would like to place a

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How to place a camera on top of the robot such that it covers a specific area around the robot? I would like to place a

How to place a camera on top of the robot such that it covers a specific area around the robot? I would like to place a

How to place a camera on top of the robot such that it covers a specific area around the robot? I would like to place a

How to place a camera on top of the robot such that it covers a specific area around the robot? I would like to place a

How to place a camera on top of the robot such that it covers a specific area around the robot? I would like to place a