[Rock-dev] accessing ports in syskit compositions via services

[Felix Rehrmann]

Hi,

I want the abstraction. My observation basically was, that when you do 
*_child in a composition, one
gets the concrete orocos object and to get a port from that, one have to 
use the orocos port name.

Given an component that has an output port named "pose_samples" giving 
RigidBodyState data.
Given it is used for an orientation data service that provides 
RigidBodyState data under the name "orientation_samples".
Then I can access that data with

     *_child.pose_samples_port

or

     *_child.as(Base::OrientationSrv).orientation_samples_port

For me that is somehow counter intuitive. I assumed that with *_child I 
access the abstraction and not the concrete object.
I would have expected that something like this would work:

*_child.orientation_samples_port

And now, I just wanted to know if there is a way, that is more straight 
forward to use the abstraction then
the second examples. Or if it is not, whether or not it would be good 
idea to make it work like that.

All the best!
Felix



On 06/25/2013 02:25 PM, Matthias Goldhoorn wrote:
> Hi,
> The whole intention about the data services is this abstraction.
> What else do you have in mind, you need to define the "generic 
> portname" anywhere...
> How else should be an abstract "portname" defined an dataservice?
>
> I mean creating an data-service is an 3-liner...
>
> Matthias
>
> On 25.06.2013 14:15, Felix Rehrmann wrote:
>> Hi,
>>
>> I have a composition (see below) that has an OrientationSrv, for which I
>> found two ways of accessing the underlying port.
>> One is via the service, the other is via the orocos task. Latter has the
>> problem that it depends on the port name of the orocos
>> task, which might not be named like the service port and in this case
>> actually is not. The access via the service is a bit uncomfortable
>> as it requires the conversion into the data service first. - Is there
>> another solution which allows to access the port via the service? Say
>> a bit more straight forward?
>>
>> Felix
>>
>> class RotateTo<  Syskit::Composition
>>
>>       add Base::Motion2DControlledSystemSrv, :as =>  'system'
>>       add Base::OrientationSrv, :as =>  'orientation'
>>
>>       argument :target_angle, :default =>  0.0
>>       argument :rate, :default =>  0.1
>>
>>       on :start do |ev|
>>           @cmd_writer = system_child.orocos_task.motion_command.writer
>>           # The orientation service knows the port under the name
>> orientation_samples.
>>           @ori_reader =
>> orientation_child.as(Base::OrientationSrv).orientation_samples_port.reader 
>>
>>           # The orocos task's port is actually called pose_samples.
>>           #@ori_reader = orientation_child.pose_samples_port.reader
>>       end
>>
>> ....
>>
>
>

-- 

  Felix Rehrmann
  Researcher
  
  DFKI Bremen
  Robotics Innovation Center
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