Support ports with default values

[adivardi]

Is your feature request related to a problem? Please describe.
Currently, Groot cannot be used for nodes with default port values.
For such nodes, Groot will either:

• Explicitly set the default value, if available in the models xml - OK, but requires propel models xml, and is tedious for repeated or complex types
• Set the port value to "" - crashes for any non-string port

So after every save in Groot, we have to manually remove these ports.

Describe the solution you'd like
According to the tutorials, ports with default values should be omitted from the XML. I think either a solution can be either:

• Groot can properly detects a port with default value and excludes it from the xml unless a value is given
• A special string value indicating this port should be omitted (e.g. N/A)

Obviously, I think the first solution is nicer.

Describe alternatives you've considered
See above

Additional context

[facontidavide]

if you can provide something that allows me to reproduce this quickly, I will try to address it

[facontidavide]

I started looking into this problem and I would like to solve it this week.

Can you provide a simple example to reproduce this problem? It is not clear to me, yet, what is going on...

[adivardi]

Sorry, I didn't have time to answer recently.
I went back and checked it, and I noticed Groot does handle default values if they are provided in the Node Model, i.e. if a value is not provided and there is a default value, Groot will not add it to the xml.
However, default values which are empty string are ignored -> so they are added to the node in the xml.

Example:
Use this xml file

<?xml version="1.0" encoding="UTF-8"?>
<root BTCPP_format="4"
      main_tree_to_execute="MainTree">
  <BehaviorTree ID="MainTree">
    <ComputePathToPose goal="{goal}"
                       planner_id="{selected_planner}"
                       path="{path}"
                       error_code_id="{compute_path_error_code}"/>
  </BehaviorTree>

  <!-- Description of Node Models (used by Groot) -->
  <TreeNodesModel>
    <Action ID="ComputePathToPose">
      <input_port name="goal">Destination to plan to</input_port>
      <input_port name="start">Use as the planner start pose instead of the current robot pose, if use_start is not false (i.e. not provided or set to true)</input_port>
      <input_port name="use_start"
                  default="false">For using or not using (i.e. ignoring) the provided start pose</input_port>
      <input_port name="planner_id">Mapped name to the planner plugin type to use</input_port>
      <input_port name="server_name">Server name</input_port>
      <input_port name="server_timeout">Server timeout</input_port>
      <output_port name="path">Path created by ComputePathToPose node</output_port>
      <output_port name="error_code_id"
                   default="0">"Compute path to pose error code"</output_port>
      <output_port name="error_msg">"Compute path to pose error message"</output_port>
    </Action>
  </TreeNodesModel>

</root>

If you open in Groot, then save it, you will get (see note about use_start below) :

<?xml version="1.0" encoding="UTF-8"?>
<root BTCPP_format="4"
      main_tree_to_execute="MainTree">
  <BehaviorTree ID="MainTree">
    <ComputePathToPose goal="{goal}"
                       start=""
                       planner_id="{selected_planner}"
                       server_name=""
                       server_timeout=""
                       path="{path}"
                       error_code_id="{compute_path_error_code}"
                       error_msg=""/>
  </BehaviorTree>

  <!-- Description of Node Models (used by Groot) -->
... remains the same...

The use_start is correctly ignored, since it has a default value false. but all the other fields whose default value is "" are added to the xml.

---

A related issue, is that when using BT::writeTreeNodesModelXML to generate the models description, it doesn't write default values for ports whose default value is "".

To replicate this, you can try nav2's node: ros2 run nav2_behavior_tree generate_nav2_tree_nodes_xml. If you check FollowPath in the resulting file, it has no default values specified. However, 3 ports do have those in the providedPorts() function

---

Finally, a somewhat related issue I noticed, is when opening the file I attached, Groot automatically fills use_start to false as a "real" value. If I want to use the default value, I have to manually delete it in Groot, at which point the text turns from black to grey, and the field will be correctly omitted from the xml.

[tony-p]

@facontidavide What is the current status of this? I believe the issue has existed since bt.CPP 4.5.x as prior to that I believe empty strings in the attributes resulted in the attribute/port being ignored.

In 4.5/4.6 we have been patching bt.CPP to replicate that behaviour, but would really like to move towards the precompiled binaries (ros distros) and then we would have to clean up the generated BTs on each save.

[facontidavide]

it should be supported now in version 1.7.0.

If you still have problems, let me know

[facontidavide]

tentatively closing this. let me know if the problem persists

[adivardi]

@facontidavide
Sorry for the slow reply, I was away for the holidays.

I have tried it again using v1.7.1 and I get the same issue exactly:

• When saving from Groot, all the ports with "" default values are added to the nodes.
• It also deletes all the default="" from the TreeNodesModel
• When opening the node model in Groot, ports with default values "" don't show any default value.
• Groot automatically fills use_start to false as a "real" value. If I want to use the default value, I have to manually delete it in Groot, at which point the text turns from black to grey

Testing configuration is pretty much the same as before (I only added default=""):

<?xml version="1.0" encoding="UTF-8"?>
<root BTCPP_format="4"
      main_tree_to_execute="MainTree">
  <BehaviorTree ID="MainTree">
    <ComputePathToPose goal="{goal}"
                       planner_id="{selected_planner}"
                       path="{path}"
                       error_code_id="{compute_path_error_code}"/>
  </BehaviorTree>

  <!-- Description of Node Models (used by Groot) -->
  <TreeNodesModel>
    <Action ID="ComputePathToPose">
      <input_port name="goal">Destination to plan to</input_port>
      <input_port name="start" default="">Use as the planner start pose instead of the current robot pose, if use_start is not false (i.e. not provided or set to true)</input_port>
      <input_port name="use_start"
                  default="false">For using or not using (i.e. ignoring) the provided start pose</input_port>
      <input_port name="planner_id">Mapped name to the planner plugin type to use</input_port>
      <input_port name="server_name" default="">Server name</input_port>
      <input_port name="server_timeout" default="">Server timeout</input_port>
      <output_port name="path">Path created by ComputePathToPose node</output_port>
      <output_port name="error_code_id"
                   default="0">"Compute path to pose error code"</output_port>
      <output_port name="error_msg">"Compute path to pose error message"</output_port>
    </Action>
  </TreeNodesModel>

</root>

[facontidavide]

have you enabled this? Anyway, I will look further into this to improve usability and use betetr defaults

[facontidavide]

@adivardi to be more specific, what I beliebe the current output IS SUPPOSED to be IDEALLY is:

  <BehaviorTree ID="MainTree">
    <ComputePathToPose goal="{goal}"
                       planner_id="{selected_planner}"
                       path="{path}"
                       error_code_id="{compute_path_error_code}"
                       error_msg=""/>
  </BehaviorTree>

because error_msg doesn't have a default.

Also, something I am noticing is that <input_port name="server_timeout" default="">Server timeout</input_port> is a little suspicious and probably wrong, since this is probably a number (?)

I am having a hard time understanding what your intent is, when using

      default=""

For a port that should have a type other than a string

[adivardi]

have you enabled this? Anyway, I will look further into this to improve usability and use betetr defaults

Ah, my bad, I didn't realize this is an option. With this enabled, it works well! Thanks for the fix!
I think with this option enabled, there is no need to add default="" in the TreeNodesModel. It also not really correct as It is not really a default, but an empty input port.

because error_msg doesn't have a default.

You are right. When left empty, it is shown as red in Groot. But when saving, it doesn't add it. Should it?

Also, something I am noticing is that <input_port name="server_timeout" default="">Server timeout</input_port> is a little suspicious and probably wrong, since this is probably a number (?)

Yeah, in this occasion it should not be default="" but just empty/unset.