This is a great point Herman. Although there is a urdf2collada tool, most of the tools developed by Willow Garage in ROS directly use URDF. We're hoping to eventually have a collada2urdf tool to resolve these issues so that a robot's data can be natively stored in collada. rosen, 2010/8/7 Herman Bruyninckx : > On Fri, 6 Aug 2010, David Lu!! wrote: > >> Hey ROS-community,I've been working with URDF extensively for awhile, and >> am >> wondering what the future is for its development. Specifically, whether >> the >> format will be extended at all to address what I perceive to be some of >> its >> limitations. >> >> I think the biggest limitation is the lack of graph support, which relates >> a >> link to two or more parent links (as opposed to the current tree >> structure). I >> believe this problem stems from KDL supporting only chains, and not >> graphs, but >> there are a number of situations where a graph structure is called for. >> The >> simplest example is a four bar linkage, which, as it stands, cannot be >> easily model led in URDF. > > COLLADA seems to be the future: it allows to model graphs, for example; it > is a real international standard; there are already ROS initiatives working > in this direction. > > KDL is also going to adopt COLLADA, in the coming year or so. > > Best regards, > > Herman Bruyninckx > >> >> One step toward fixing the problem could involve making some joints >> dependent on >> other joints. For the case of a parallelogram-shaped 4 bar, three of the >> joints >> could depend on one joint, but there is currently no support for that >> either. A >> similar situation involves gears/pulleys and other motion transferring >> mechanisms, i.e. two gears, each connected to a base with a continuous >> joint, >> and the angle of joint for the second gear is 4 times the angle for the >> first. >> >> Having now tried to get collision detection working as well, it seems odd >> to >> have three different structures to specify the hierarchy of the machine. >> Its >> specified once in the URDF, and then separate groups are defined via >> parameters >> to define groups. Some of these groups coincide with whole xacro macros >> too. >> While I see that these distinctions may often need to be customized, it >> seems >> like it would be easier to do the customization via parameter, and not use >> the >> parameters to redefine everything again. >> >> The last thing that concerns me is the PR2 specific extensions. I'm not >> exactly >> clear what they lend to the PR2, but I'm also not clear why they wouldn't >> apply >> to other robots. >> >> [As an aside, does anyone know where the xml schema are for urdf? The PR2 >> file >> links to http://playerstage.sourceforge.net/gazebo/xmlschema/, but there's >> nothing there.] >> >> What I'm wondering is whether any of these issues are currently being >> addressed, >> or whether I should work around them (either in my own code or in the ROS >> repository). Hopefully this will spark a discussion on any other hurdles >> people >> are having with URDF. >> >> Thanks, >> David!! >> >> >> > > -- >  K.U.Leuven, Mechanical Eng., Mechatronics & Robotics Research Group >     Tel: +32 16 328056 >  EURON Coordinator (European Robotics Research Network) > >  Open Realtime Control Services >  Associate Editor JOSER , IJRR > _______________________________________________ > ros-users mailing list > ros-users@code.ros.org > https://code.ros.org/mailman/listinfo/ros-users > >