FIWARE FIROS Publish cmd_vel from Non-ROS-World - ros

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.