FIWARE FIROS Publish cmd_vel from Non-ROS-World

Question

Within firos turtlesim example (https://firos.readthedocs.io/en/latest/install/turtlesim-example.html) I'm trying to publish msg on /turtle1/cmd_vel topic from Non-ROS-World trough POST request in order to move the robot.

However I'm not sure how to do that because when I start firos/core.py the list of entities created is:

{"id":".turtle1.pose","type":"turtlesim%2FPose","angular_velocity":{"type":"number","value":0,"metadata":{"dataType":{"type":"dataType","value":"float32"}}},"linear_velocity":{"type":"number","value":0,"metadata":{"dataType":{"type":"dataType","value":"float32"}}},"theta":{"type":"number","value":0,"metadata":{"dataType":{"type":"dataType","value":"float32"}}},"x":{"type":"number","value":5.544444561,"metadata":{"dataType":{"type":"dataType","value":"float32"}}},"y":{"type":"number","value":5.544444561,"metadata":{"dataType":{"type":"dataType","value":"float32"}}}}

And the list of subscriptions is:

{"id":"XXXX","expires":"2021-06-09T22:10:17.000Z","status":"active","subject":{"entities":[{"id":".turtle1.cmd_vel","type":"geometry_msgs%2FTwist"}],"condition":{"attrs":[]}},"notification":{"attrs":["linear","angular"],"onlyChangedAttrs":false,"attrsFormat":"normalized","http":{"url":"http://XXX.XXX.X.XXX:YYYYY"}}}

None entity with .turtle1.cmd_vel id is created, so that I don't know how to update for example linear attr. Do I have to create .turtle1.cmd_vel entity manually first and update attr after? I tried it:

curl -iX POST \
  'http://localhost:1026/v2/entities' \
  -H 'Content-Type: application/json' \
  -d '
{
    "id": ".turtle1.cmd_vel",
    "type": "geometry_msgs%2FTwist",
    "linear": {
        "type": "float64",
        "value": {
            "x": "1",
            "y": "0",
            "z": "0"
        }
    },
    "angular": {
        "type": "float64",
        "value": {
             "x": "0",
             "y": "0",
             "z": "0"
        }
    }
}'

but I got errors.

Answer 1

Finally I solved the problem as follows:

POST the entity:

curl -iX POST \
  'http://localhost:1026/v2/entities' \
  -H 'Content-Type: application/json' \
  -d '
{
    "id":".turtle1.cmd_vel",
    "type":"geometry_msgs%2FTwist",
    
    "angular":{
        "type":"geometry_msgs%2FVector3",
        "value":{
            "y":{
                "type":"number",
                "value":0.0
            },
            "x":{
                "type":"number",
                "value":0.0
            },
            "z":{
                "type":"number",
                "value":0.0
            }
        },
        "metadata":{
            "dataType":{
                "type":"dataType",
                "value":{
                    "y":"float64",
                    "x":"float64",
                    "z":"float64"
                }
            }
        }
    },
    "linear":{
        "type":"geometry_msgs%2FVector3",
        "value":{
            "y":{
                "type":"number",
                "value":0.0
            },
            "x":{
                "type":"number",
                "value":0.0
            },
            "z":{
                "type":"number",
                "value":0.0
            }
        },
        "metadata":{
            "dataType":{
                "type":"dataType",
                "value":{
                    "y":"float64",
                    "x":"float64",
                    "z":"float64"
                }
            }
        }
    }
}'

To update values:

curl -iX PATCH \
  --url 'http://localhost:1026/v2/entities/.turtle1.cmd_vel/attrs' \
  --header 'Content-Type: application/json' \
  --data-raw ' {
    "angular": {
        "type":"geometry_msgs%2FVector3",
        "value":{
            "y":{
                "type":"number",
                "value": 0.0
            },
            "x":{
                "type":"number",
                "value": 0.0
            },
            "z":{
                "type":"number",
                "value": 0.0
            }
        },
        "metadata":{
            "dataType":{
                "type":"dataType",
                "value":{
                    "y":"float64",
                    "x":"float64",
                    "z":"float64"
                }
            }
        }
    },
    "linear": {
        "type":"geometry_msgs%2FVector3",
        "value":{
            "y":{
                "type":"number",
                "value": 8.0
            },
            "x":{
                "type":"number",
                "value": 8.0
            },
            "z":{
                "type":"number",
                "value": 8.0
            }
        },
        "metadata":{
            "dataType":{
                "type":"dataType",
                "value":{
                    "y":"float64",
                    "x":"float64",
                    "z":"float64"
                }
            }
        }
    }
}'

Note about updating entity:

It cannot directly update the sub-attribute "x" (from "linear" attr) on its own, it needs to resupply the whole JSON Object.

The reasoning behind this is as follows: NGSI just deals with Properties and Relationships - it is an abstraction layer for interoperability. The Property "linear" is an atomic unit hence you either change the whole "linear" or none of it. The value of "linear" is in this case a JSON object.