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Hello now we will learn about ros service

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ros service is another form of
communications unlike the ros topic it does not

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 sends a stream of the data in this service
do not communicate via requests and the responce

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and here you can see the nice illustration where
we have a service client it sends a message to

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the service server and then it responses back
that will be received by the service client and

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here tow nodes are communicating and it can be
multiple Node and here you can see there are

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multiple nodes they are communicating
our one service open up the terminal

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okay we will run our ros2 run turtlesim

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Turtlesim node now we will see what are the
services are available ros2 service list

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just like we have seen in ros2
topic list ros2 node list

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now we are seeing ros service list so
here are a bunch of services that we can

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utilize we have to find out the type
ros2 service type clear hit enter

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and here we have the service type of clear
service if you want to see the type of all

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the services in the list what we will do type
ros2 service list -t it will display the

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type of all these Services okay if we want
to find out all the services with the same type

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okay we can also do that ros2 service
find and then the type of the service

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yes here we can see there are two services
that have similar type just like we saw

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the interface in ros topic it can also show
the interface in ros service ros2 interface

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show and this service type which
was this is the service type

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and dot SRV indicating the service it
does not have any type of request and

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responce and spawn service has
this type I will just copy and

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paste it here dot SRV so here we can see it has
a lot of things in it the things that will see

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here are the request they are separated by
these three dashes and here we have response

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if we want to spawn our turtlesim in a window
we will have to input the X Y and the Theta of

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the robot in the turtlesim window and we
also have to mention the name of the turtle and

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in the return it will just give us the name the
next terminal and we will launch uh the teleop

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yes here we can try the robot around and
now we will see how the clear service Works

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ros service this minus t and we will see the
type of this and we have to is utilize this

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ros2 service call and we are going to call
this service which is declared clear and the

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type of the service which is STD slash
SRV slash empty we will just call

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and it has erased the path that turtlesim drawn
now I would like to utilize the spawn service which is

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here and this is the type of this service we will
again see the interface ros2 interface show

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the type of the service SRV

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and it has displayed all the constant values that

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it takes and we will have to input ros2 service call spawn and the service type

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and then again the same Convention as we published
the topic in the previous lecture and we will

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type bracket X how do we know we have to input
the X here it's mentioned uh X colon space 2.5

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comma

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y colon 3.4 comma parameter that we have to
mention Theta colon 1 comma name colon inverted

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commas and we can mention here like turtle
underscore 2. and we will just close the bracket

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fail to populate the field spawn request object
has no attribute here I think the this face is

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missing here yeah so I will just give it a
space here and also there is a space in the name

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yeah now it is called here I can move it here
if I want to move uh the other Turtle I will

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have to remap the ros topic of turtle one slash
cmd_vel as we have done in the previous lecture

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there is also a method to call this
service as we have went through the rqt

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here we have the service caller
we can see the spawn service

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and we have this Turtle here if we mention like

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there is another turtle so you can bring
as many Turtle as you want so that was

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all about the service so if you have learned
how to find out the type of a service how to

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find the services that have the same type and

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how to show the interface of a
service and how to call it