[cob_grasp_generation] Convert URDF into OpenRAVE model for cob_grasp_generation

[fmessmer]

Testing parts of what is proposed in #70

This is documenting my trials in order to use the cob_grasp_generation package with any gripper modelled as URDF (related branch is https://github.com/ipa-fxm/cob_manipulation/tree/wip/support_urdf_gripper)

Don't know whether it will work in the end 😉
@ipa-bfb @fmessmer FYI

[fmessmer]

How to create an OpenRAVE model for a gripper with available URDF macro:

1. Create a new "gripper robot" that just consists of the gripper macro like below and put it into cob_grasp_generation/files/gripper/:

   <?xml version="1.0"?>
   <robot xmlns:xacro="http://www.ros.org/wiki/xacro"
      name="sdh" >
   
   <xacro:include filename="$(find schunk_description)/urdf/sdh/sdh.urdf.xacro" />
   
   <link name="base_link"/>
   
   <xacro:schunk_sdh name="sdh" parent="base_link">
     <origin xyz="0 0 0" rpy="0 0 0" />
   </xacro:schunk_sdh>
   
   </robot>
   

2. Convert to URDF via rosrun xacro xacro.py sdh.urdf.xacro > sdh.urdf

3. Convert to Collada via rosrun collada_urdf urdf_to_collada sdh.urdf sdh.dae (http://wiki.ros.org/collada_urdf#urdf_to_collada_command-line_tool)

4. Create manifest.xml for your Collada model like so:
   `

   <dae_root>./sdh.dae</dae_root>
   `

5. Zip Collada and manifest with archive manager (use zip compression) then rename the .zip to .zae (http://openrave-users-list.185357.n3.nabble.com/COLLADA-format-editor-for-zae-td3257031.html)

6. Create a new OpenRAVE env.xml like so:

   <Environment>
   
   <!-- Roboter -->
   <Robot file="gripper/sdh.zae" name="sdh">
     <translation>-1.52295 0.50617 0.01</translation>
     <RotationAxis>0 0 1 180</RotationAxis>
   </Robot>
   
   </Environment>
   

7. Make sure you have cob_grasp_generation/files included in your OPENRAVE_DATA env variable

[fmessmer]

Hmm, while the model then can be loaded into OpenRAVE (see below), I was not able to generate/show/query any grasp (continuing branch https://github.com/ipa-fxm/cob_manipulation/tree/wip/or_env_vs_gripper_type)

Appearently, collada_urdf does not generate/convert essential things like manipulator definitions and such. I guess without intensive investigation, manually extending the dae so that it can be used together with cob_grasp_generation is not suitable...