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Open source question and answer forum written in Python and Django

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    i have to share some flags which do not change much among 4-5 nodes .A node named SERVER is changing the flags and thats very rarely. I have to check the value of flags at the rate of 10hz in other nodes . So which is the best way of implementing it. I already thought about some options like :
    1. Publishing of flags on a topic by SERVER at a frequency of 2-3 Hz.
    2. Using service call to update the value of flags in the nodes which have their own copy of flags.
    3. Using parameter server.
    4 Shared memory.
    I do not think 1st option is the good one.

    I have some doubts regarding this:
    a). If i used the second option,will cpu`s time be wasted in looking for queue for the message arrival?
    b). Is third option good for getting the value of parameter frequently ?
    c). What about shared memory? I have read that shared memory is the fastest mode of interprocess communication.

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    I would like to set a parameter in a launch file but only if the respective parameter is not yet set. (The parameter value I would like to set in the launch file is kind of default but maybe the user has already set it to something smarter before the launch so i do not want to override the user value.) Is that possible? Or is it possible to retrieve a ros param inside a launch file in order of checking if it exists?

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    hi all, i'm trying to create a sensor camera on [gazebo](http://www.ros.org/wiki/gazebo), but i have this message on the terminal when i run the launch file: [ERROR] [1323711066.531080823]: Could not find parameter robot_description on parameter server [ERROR] [1323711066.531205567]: Could not generate robot model [ERROR] [1323711066.531238167]: Failed to extract kdl tree from xml robot description [robot_state_publisher-4] process has died [pid 2161, exit code 255]. log files: /home/mauro/.ros/log/0edc0fb2-24e7-11e1-ba97-0016ea548718/robot_state_publisher-4*.log i created a launch file: the file my_camera.lauch is: the file my_camera.urdf .xacro is: true 640 480R8G8B8900.0110020.0true20.0finger_tip_cam/imagefinger_tip_cam/camera_infofinger_tip_camera_linktrueGazebo/Blue Erratic/YellowErratic/YellowErratic/Yellow

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    Example: I have always the same node type, lets say with a parameter named "shape" I make one node (node A) with shape = "square" I make a second node (node B) with shape = "circle" in the console if i did rosparam list i would see /nodeA/shape /nodeB/shape and if i did rosparam get /nodeA/shape i would see "Square", but is it possible in my test file, my cpp file, to use some form of get parameter when creating a node, so that I can see that node A shape is "Square"? pseudocode: if(&newNode/shape == &nodeA/shape) kill(newNode, SIGINT) Overall, i want to be able to test and see if a value of the parameter exists, and then if it exists, i will do a kill(pid, SIGINT). But i am having a hard time accessing the parameter value of the other nodes.

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    Hi, Is there a way to avoid overwriting parameters when being loaded from a launchfile using a YAML file? For example, I have two YAML files like the following: config1.yaml topics: - topic: topic1 type: geometry_msgs/Twist - topic: topic2 type: std_msgs/Empty config2.yaml topics: - topic: topic3 type: geometry_msgs/Twist - topic: topic4 type: std_msgs/Empty and want to have the 4 topics loaded under the `topics` parameter. I know that namespacing is the way it's normally done to separate parameters with the same name, but I'm looking for some other way. Thanks!

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    Does anyone know if there is an equivalent of the console command "rosparam get 'parameter'" or "rosparam list" that can be written in to a .launch file. Wanting to check if a parameter is set or exists. So i was thinking that I could use an unless or if check but I don't know how to tell it to check if it exists in the parameter server... Please someone help hahaha

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    Is it possible to dump rosparam when the node stops using roslaunch? On the [wiki](http://wiki.ros.org/roslaunch/XML/param) it is stated, that "dump" and "delete" commands run *before* load, which is exactly opposite from what I want. Currently I do it manually like this: void dumpRooms(std::string yamlFile) { system("rosparam dump -v "+yamlFile.c_str()+" my_namespace"); }

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  • 11/03/15--23:42: reading parameter in c
  • Hello, I am trying to read parameters in my program based on this example http://wiki.ros.org/Parameter%20Server Here is code snippet std::string my_number; nh_.getParam("my_number",my_number); ROS_INFO("\n My Number %s",my_number.c_str()); And I am calling like this rosrun mypkg my_node my_number:=5 This value is not getting read. Please help, how can I read in my C program. Thanks, Hemant

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    Hello, is there a way to generate the content of the reconfiguration GUI during runtime? For instance a drop down list where it's content is decided after program start. I know the variables are declared in the .cfg and I need to compile the package in order to get the according header files. But is it possible to assign a created parameter on the parameter server to, for instance a drop down list? Thanks in advance, Chris

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    Hello everyone ! I use the eband_local_planner for the navigation of my robot in simulation.
    The problem is that when I type the command `rosparam list`, I can't see the parameters of my planner.
    It is the same if I type `rosparam get parameter_name`, I get a message which says that the requested parameter does not exist.
    However, if I load these invisible parameters from a YAML file, I can see their effects but they doesn't appear in the parameter server through the previously indicated commands.
    They doesn't appear neither using the `rosrun rqt_reconfigure rqt_reconfigure` command.
    My question is: How to have this visibility ?
    I ask that because I want to be able to access these parameters in the parameter server in order to modify the behaviour of my robot from a C++ node. If anyone can help me, I will be grateful,
    lfr

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    I'm porting a system to ROS that will be composed of several nodes linked by topics in a chain-like structure, in a way that each node produces some data to be consumed by the callback of the next node. The problem I'm facing is that some of the nodes set variables that represent "system states" that influence the behavior of other nodes later in the chain (not the next imediate one). I'm wondering what is the best way to implement such thing on ROS. I though about using the parameter server with getParam() and setParam() for that, but I read in the [Parameter Server page](http://wiki.ros.org/Parameter%20Server) that: > As it is not designed for high-performance, it is best used for static, non-binary data such as configuration parameters. So I'm not sure if I should use it for these state variables. I also read about getCachedParam(), but I think the same doubt about the performance applies. I also saw [dynamic_reconfigure](http://wiki.ros.org/dynamic_reconfigure), but I don't know if it was developed for this kind of scenario. Could anyone tell me what would be the best way to implement this in ROS?

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    Hi, I implemented an application in which I have three robots, each one running it's own control node, and the ROS master running on a notebook. The control node is the same, however each robot runs its own instance of it, with a different namespace. There are some parameters that are used by the control algorithm. The nodes subscribe to a specific topic and I am able to change the value of these parameters by publishing messages to this topic: when the robots receive the message they change the variable to its new value. The idea is that, although each robot has its own copy of the variable representing the parameter, all robots always use the same values, so the variables must be synchronized. Is there a best way or good practice to implement something like that? I thought maybe using the parameter server to store the current value of each parameter, but I am not sure if this is the best idea.

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    The [rosserial parameter](http://wiki.ros.org/rosserial/Overview/Parameters) documentation shows getting parameters from the parameter server, but not setting parameters. Is there a way to set parameters from rosserial? I'm guessing not, since the [`NodeHandle` class](https://github.com/ros-drivers/rosserial/blob/46a7d8be2af4a5fae0f9c324369eab31394c0d4e/rosserial_client/src/ros_lib/ros/node_handle.h) only has parameter getters, not setters, but I'm wondering if anything's in the works or why this hasn't been a priority yet.

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    Each time I read and write from and to the servos in my symmetric robot, I want to check a mode that determines which servos to talk to (the frames of this robot can change while it's running). Because the reading and writing happens continuously through topics, I want to make sure this checking adds as little overhead as possible. I considered two solutions: services and a parameter server. From what I understand, [services](http://wiki.ros.org/Services) seem to be able to do this quickly, but it looks like they can't deliver a different response, as when the mode changes. A [Parameter Server](http://wiki.ros.org/Parameter%20Server) can do the trick, but the wiki explicitly states that it's not meant for high-performance and dynamic data. Are there any other solutions or am I overestimating the overhead with the parameter server?

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    I'm trying to pass a variable of type "double" to a roscpp node as a command-line variable. E.g. $ rosrun package_name node_name parameter:=0.1 And then access the parameter within the node like so: ros::NodeHandle nh; double parameter; nh.param("parameter", parameter, 0.5); However this doesn't work, and instead I get the following error: terminate called after throwing an instance of 'ros::InvalidNameException' what(): Character [0] is not valid as the first character in Graph Resource Name [0.1]. Valid characters are a-z, A-Z, / and in some cases ~. I'm sure I've just got the wrong syntax, either within the node or when entering the parameter. I've thoroughly read the wiki pages on [NodeHandle](http://wiki.ros.org/roscpp/Overview/NodeHandles) and the [Parameter Server](http://wiki.ros.org/roscpp/Overview/Parameter%20Server), but I haven't found a solution. Everything I've tried either produces the error above, or my ignores the input and sets the parameter to it's default value (0.5). Is anyone able to correct my syntax? Thanks in advance.

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    Where on disk does the [parameter server](http://wiki.ros.org/Parameter%20Server) store data to when it's not running?

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    Hi, I was wondering what experiences people have had from using the parameter server... 1. What cases must you use the parameter server? What types of data would you not read through the parameter server? 2. What cases should you use some other methods, like a shared memory file? 3. When should you use command line arguments? 4. What other options do you have in addition to these? Thank you

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