[store points] evaluate format

[jschleicher]

for easy storage

• humand-readable / edit(?)
• easy to import into python-(API)-script
• allows names and cartesian / joint positions

[Hardthof]

• plain text - python dict
  • message_converter can serialize a ROS message object into a dict and vice versa
  • pprint.pformat() formats the dict with line-breaks and indentation
  • eval() or ast.literal_eval() can read the dict back and message_converter makes a ROS type from it
• rosbag (ROS-native)
  • abuse topic names as position names
  • unnecessary timestamp
  • intrinsic ROS message representation
• json (different format than ROS that typically uses yaml)
• pickle converts objects into a binary format (non-human-readable)

[Hardthof]

Open Questions:

• Consistency with robot_model? E.g. loading a different gripper / tool, (major) changes in workspace
• how to handle consistency when editing files manually (joints vs. pose)

[jschleicher]

To store direct python structures like this

position_start = Pose()

position_start.position.x = 0.73
position_start.position.y = -0.2
position_start.position.z  = 0.3

would give additional advantages:

• easy calculations (but lost on overwriting) position_machine.z = position_start.z + 0.3
• direct import positions as p without additional loader module
• syntax completion would know, which variable names exist
• intrinsic semantics (type-knowledge together with values)

Should we extend rospy_message_converter to allow such output?
Quick try didn't find a straight-forward way: Print a string representation with native rospy message overloads of repr() isn't parsable using eval() afterwards...

[DamKoVosh]

We could do something along those lines:

import inspect
import genpy

def recreate_rep(msg):
   if not isinstance(msg, genpy.Message):
      return str(msg)

   arguments = {}
   for a in dir(msg):
      if not (a.startswith("_") or "serialize" in a) and not callable(getattr(msg, a)):
         arguments[a] = recreate_rep(getattr(msg, a))
   
   args_string = ', '.join('{}={}'.format(key, value) for key, value in arguments.items())
   repr_string = "%s(%s)" % (msg.__class__.__name__ , args_string)
   return repr_string

so this

from geometry_msgs.msg import Pose, Point
recreate_rep(Pose(position=Point(x=2, z=3)))

results in

'Pose(position=Point(y=0.0, x=2, z=3), orientation=Quaternion(y=0.0, x=0.0, z=0.0, w=0.0))'

and eval works again.