Get Parameter
Get values from ROS parameter server
- Library:
ROS Toolbox / ROS
Description
The Get Parameter block outputs the value of the specified ROS parameter. The block uses the ROS node of the Simulink® model to connect to the ROS network. This node is created when you run the model and is deleted when the model terminates. If the model does not have a node, the block creates one.
On each sample hit, the block checks the ROS parameter server for the specified ROS parameter and outputs its value.
Ports
Output
Value — Parameter value
scalar | logical | uint8 array
Parameter value from the ROS network. The value depends on the Data type parameter.
ErrorCode — Status of ROS parameter
0 | 1 | 2 | 3
Status of ROS parameter, specified as one of the following:
0 — ROS parameter retrieved successfully. The retrieved value is output in the Value port.
1 — No ROS parameter with specified name found. If there is no known value, Value is set to the last received value or to Initial value.
2 — ROS parameter retrieved, but its type is different than the specified Data type. If there is no known value, Value is set to the last received value or to Initial value.
3 — For string parameters, the incoming string has been truncated based on the specified length.
Length — Length of string parameter
integer
Length of the string parameter, returned as an integer. This
length is the number of elements of the uint8 array
or the number of characters in the string that you cast to uint8.
Note
When getting string parameters from the ROS network, an ASCII value of 13 returns an error due to its incompatible character type.
Dependencies
To enable this port, set the Data type to uint8[]
(string).
Parameters
Source — Source for specifying the parameter name
Select from ROS network | Specify your own
Source for specifying the parameter name as one of the following:
Select from ROS network— Use Select to select a parameter name. The Data type parameter is set automatically. You must be connected to a ROS network.Specify your own— Enter a parameter name in Name and specify its data type in Data type. You must match a parameter name exactly.
Name — Parameter name
string
Parameter name to get from the ROS network, specified as a string.
When Source is set to Select from
ROS network, use Select to select
an existing parameter. You must be connected to a ROS network to get
a list of parameters. Otherwise, specify the parameter and data type.
Parameter name strings must follow the rules of ROS graph names. Valid names have these characteristics:
The first character is an alpha character ([a-z|A-Z]), tilde (~), or forward slash (/).
Subsequent characters are alphanumeric ([0-9|a-z|A-Z]), underscores(_), or forward slashes (/).
Data type — Data type of your parameter
double | int32 | boolean | uint8[] (string)
Data type of your parameter, specified as a string. The uint8[]
(string) enables the Maximum length parameter.
Note
The uint8[] (string) data type is an array of ASCII
values corresponding to the characters in a string. When getting string
parameters, you can create a MATLAB Function block
to compare the string to a desired parameter value. For more
information, see ROS Parameters in Simulink.
Data Types: double | int32 | Boolean | uint8
Maximum length — Maximum length of the uint8 array
scalar
Maximum length of the uint8 array, specified
as a scalar. If the parameter string has a length greater than Maximum
length, the ErrorCode output is set
to 3.
Dependencies
To enable this port, set the Data type to uint8[]
(string).
Initial value — Default parameter value output
double | int32 | boolean | uint8
Default parameter value output from when an error occurs and no valid value has been received from the parameter server. The data type must match the specified Data type.
Sample time — Interval between outputs
inf (default) | scalar
Interval between outputs, specified as a scalar. This default
value indicates that the block output never changes. Using this value
speeds simulation and code generation by eliminating the need to recompute
the block output. Otherwise, the block outputs a new blank message
at each interval of Sample time.
For more information, see Specify Sample Time (Simulink).
Show ErrorCode output port — Display error code output
on | off
To enable error code output, select this parameter. When you clear this parameter, the ErrorCode output port is removed from the block. The status options are:
0 — ROS parameter retrieved successfully. The retrieved value is output in the Value port.
1 — No ROS parameter with specified name found. If there is no known value, Value is set to the last received value or to Initial value.
2 — ROS parameter retrieved, but its type is different than the specified Data type. If there is no known value, Value is set to the last received value or to Initial value.
3 — For string parameters, the incoming string has been truncated based on the specified length.