[Rock-dev] joint_dispatcher

[Jakob Schwendner]

On September 25, 2013 at 5:28 PM Dennis Mronga <dennis.mronga at dfki.de> wrote:
> Hi,
>
> I recently stumbled across the joint_dispatcher component, which
> "nearly" seems to be what I need. However, it seems a bit complicated to
> configure and I think it does not cover the following cases:
I can second the complicated to configure bit :) Since I got it working, it was
working fine for my case.

>
> 1. Send only a subset of all available joints to the input ports and
> dispatch them correctly to the outputs, instead of always expecting all
> available joints. Right now, the component crashes with an unhandled
> exception, if you do not send all joints to the input port.
I guess this could be easily fixed in the component. In my opinion the best way
would be to make this configurable, e.g. AllowPartialJointUpdate = true or
something similar.

>
> 2. Get input from different sources and dispatch arbitrary subsets of
> the inputs. E.g. if you have the joint state of the wheels and the joint
> state of the manipulator as inputs and you want to output the port
> "odometry" containing only the wheels, "manipulator" containing only the
> manipulator and "full_joint_state" containing all joints.
Yes, this I couldn't get working either, and would have needed. Currently I am
running two components in parallel to get this behaviour.

>
> Generally I think it would be nicest, if you just have to configure the
> input and output ports with the corresponding joint names and the
> distribution of the joint states is done by the component according to
> the joint names. However, I think that would reduce a bit the
> capabilities of the component!?
Yes, would have thought the same. It gets a little complicated because of the
duality of the names/index mechanism in the Joints class.
But, even when you don't want to use names in the Joints port, it would imo be
ok to name them for the sake of the dispatcher.

>
> Before creating a branch and adding the functionality that I need, I
> would like to know if anyone of you has used the joint_dispatcher and
> has some remarks!?
I had a discussion with Sylvain on this subject, which I guess would have been
good to put on the mailing list. The agreement was, though, that changing the
way the module is configured would be nice.

My preferred configuration would be something like:

struct DispatchOutput
{
string name; // name of dynamic port
vector<string> jointNames; // list of joint names
vector<string> internalNames; // list of internal names for the joints
}

struct DispatchInput
{
string name; // name of dynamic port
vector<string> internalNames; // list of internal names for the joints
vector<string> jointNames; // list of external joint names
}

module
{
vector<DispatchInput> inputs;
vector<DispatchOutput> outputs;
}

the linking between input and output would be done on the internal names. For
the index based Joints structs (e.g. no names), this would name the joints
internally. The reason for not just using a single names vector per input/output
is that you could have a configuration where the joint names are the same two
different input ports, or that you would want to rename the output ports. On the
other hand, maybe we should just not allow this... Thoughts?

cheers,

Jakob

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