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tutorials:beginner:motion_designators [2019/03/07 11:44] – [Designators: an overview] gkazhoyatutorials:beginner:motion_designators [2022/02/25 23:14] (current) – [Creating motion designators for the TurtleSim] schimpf
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 **Description:** In this tutorial you will learn what designators are, and in particular, work with motion designators: you will learn how to define one and how to use it. **Description:** In this tutorial you will learn what designators are, and in particular, work with motion designators: you will learn how to define one and how to use it.
  
-**Previous Tutorial:** [[tutorials:beginner:simple_plans|Implementing simple plans to move a turtle]]\\+**Previous Tutorial:** [[tutorials:beginner:cram_prolog|Using Prolog for reasoning]]\\
 **Next Tutorial:** [[tutorials:beginner:process_modules_2|Creating process modules]] **Next Tutorial:** [[tutorials:beginner:process_modules_2|Creating process modules]]
 +
 +To run the code in the tutuorial the roscore and the turtlesim need to be started in the terminal. Each in their own tab. 
 +<code bash>
 +$ roscore
 +</code>
 +<code bash>
 +$ rosrun turtlesim turtlesim_node
 +</code>
  
 ===== Designators: an overview ===== ===== Designators: an overview =====
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 <code lisp> <code lisp>
-(defparameter spy-location (desig:a location (to see) (object ?prime-minister)))+(defparameter *spy-location(desig:a location (to see) (object ?prime-minister)))
 </code> </code>
  
 (Do not add this code to your tutorial files, it is meant simply for illustration here.) (Do not add this code to your tutorial files, it is meant simply for illustration here.)
  
-This line of code creates a location designator (''spy-location'') which "knows" of the given object (''?prime-minister'', which we assume is an already defined object designator), and knows that its purpose is to see the object. We do not actually specify a location in terms of coordinates at this moment. When we do want to find a suitable set of coordinates for this location, we would call+This line of code creates a location designator (''*spy-location*'') which "knows" of the given object (''?prime-minister'', which we assume is an already defined object designator), and knows that its purpose is to see the object. We do not actually specify a location in terms of coordinates at this moment. When we do want to find a suitable set of coordinates for this location, we would call
  
 <code lisp> <code lisp>
-(reference spy-location)+(reference *spy-location*)
 </code> </code>
  
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 </code> </code>
  
-In your ''cram-beginner-tutorial.asd'' file, on the '':depends-on'' line, add dependencies to ''cram-designators'' and ''cram-prolog''. Let's also create a new source file for the code in this tutorial (under ''src'' directory), call it ''motion-designators.lisp''. We will need to add the file to the '':components'' of the ''src'' module in your ''cram-beginner-tutorial.asd'', which should now look something like this:+In your ''cram-my-beginner-tutorial.asd'' file, on the '':depends-on'' line, add dependencies to ''cram-designators'' and ''cram-prolog''. Let's also create a new source file for the code in this tutorial (under ''src'' directory), call it ''motion-designators.lisp''. It can be empty for now. We will need to add the file to the '':components'' of the ''src'' module in your ''cram-my-beginner-tutorial.asd'', which should now look something like this:
  
 <code lisp> <code lisp>
-(defsystem cram-beginner-tutorial +(defsystem cram-my-beginner-tutorial 
-  :depends-on (cram-language roslisp turtlesim-msg geometry_msgs-msg cl-transforms+  :depends-on (cram-language roslisp turtlesim-msg turtlesim-srv 
 +                             geometry_msgs-msg cl-transforms
                              cram-designators cram-prolog)                              cram-designators cram-prolog)
   :components   :components
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 <code lisp> <code lisp>
-(defpackage :cram-beginner-tutorial+(defpackage :cram-my-beginner-tutorial
   (:nicknames :tut)   (:nicknames :tut)
   (:use :cpl :roslisp :cl-transforms :cram-designators)   (:use :cpl :roslisp :cl-transforms :cram-designators)
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 </code> </code>
  
-Now, reload the tutorial in ''roslisp_repl'' (which also loads the newly added dependencies).+Now, reload the tutorial in ''roslisp_repl'' (which also loads the newly added dependencies)
 + 
 +<code lisp> 
 +PROLOG> (ros-load:load-system "cram_my_beginner_tutorial" :cram-my-beginner-tutorial) 
 +PROLOG> (in-package :tut) 
 +</code>
  
 ==== Creating a motion designator ==== ==== Creating a motion designator ====
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 <code lisp> <code lisp>
-TUT> (defparameter my-desig (desig:a motion (type driving) (speed 1.5))) +TUT> (defparameter *my-desig(desig:a motion (type driving) (speed 1.5))) 
-MY-DESIG +*MY-DESIG* 
-TUT> (desig-prop-value my-desig :speed)+TUT> (desig-prop-value *my-desig:speed)
 1.5 1.5
 </code> </code>
 +
 +We call the variable ''*my-desig*'' with asterisks as this is the common convention in Common Lisp for naming global variables.
  
 We use the ''a'' macro to create designators. Internally it uses the ''make-designator'' function to create a designator of the specified type. The macro allows us to write cleaner code for designator creation. We use the ''a'' macro to create designators. Internally it uses the ''make-designator'' function to create a designator of the specified type. The macro allows us to write cleaner code for designator creation.
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 <code lisp> <code lisp>
-TUT> (reference my-desig)+TUT> (reference *my-desig*)
 Cannot resolve motion designator #<MOTION-DESIGNATOR ((TYPE Cannot resolve motion designator #<MOTION-DESIGNATOR ((TYPE
                                                        DRIVING)                                                        DRIVING)
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 ==== Defining inference rules for designators ==== ==== Defining inference rules for designators ====
 +
 +The function ''reference'' uses the CRAM Prolog engine to ground a motion designator into specific motion parameters.
 +CRAM Prolog engine is a Prolog interpreter / compiler implemented as a domain-specific language within Lisp.
 +To learn more about CRAM Prolog look at the [[cram_prolog|Using Prolog for reasoning]] tutorial.
 +To ''reference'' a motion designator, ''motion-grounding'' Prolog rule is being called on the given designator and the rule binds a tuple of command and specific motion parameters to its second argument.
  
 Append the following to your ''motion-designators.lisp'' file: Append the following to your ''motion-designators.lisp'' file:
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 Let's see what this code does. The defstruct declares a structure type to hold values resulting from the inference. It's an instantiation of our motion in a space of (possibly) continuous parameters, which we deduce from a symbolic description of the designator via rules given in the def-fact-group. Let's see what this code does. The defstruct declares a structure type to hold values resulting from the inference. It's an instantiation of our motion in a space of (possibly) continuous parameters, which we deduce from a symbolic description of the designator via rules given in the def-fact-group.
  
-As for the inference rules themselves, these are Prolog code embedded in Lisp, for it is Prolog that powers the inference behind designator resolution. To learn more about CRAM Prolog look at the [[cram_prolog|Using Prolog for reasoning]] tutorial. The ''def-fact-group'' is a collection of several rules, each of similar structure, so it helps to look at one of them in more detail:+As for the inference rules themselves, these are Prolog code embedded in Lisp, for it is Prolog that powers the inference behind designator resolution. The ''def-fact-group'' is a collection of several rules, each of similar structure, so it helps to look at one of them in more detail:
  
 <code lisp> <code lisp>
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 <code lisp> <code lisp>
-TUT> (defparameter my-desig2 (desig:a motion (type driving) (speed 1.5) (angle 2))) +TUT> (defparameter *my-desig2(desig:a motion (type driving) (speed 1.5) (angle 2))) 
-MY-DESIG2 +*MY-DESIG2 
-TUT> (reference my-desig2)+TUT> (reference *my-desig2*)
 (DRIVE #S(TURTLE-MOTION :SPEED 1.5 :ANGLE 2)) (DRIVE #S(TURTLE-MOTION :SPEED 1.5 :ANGLE 2))
 </code> </code>
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 <code lisp> <code lisp>
 TUT> (desig:a motion (type moving) (goal (1 1 0))) TUT> (desig:a motion (type moving) (goal (1 1 0)))
-#<MOTION-DESIGNATOR ((:TYPE :MOVING) (:GOAL (1 1 0))) {10042C61F3}>+#<MOTION 
 +    (TYPE MOVING) 
 +    (GOAL (1 1 0))>
 </code> </code>
  
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 <code lisp> <code lisp>
-TUT> (defparameter my-desig3 (desig:a motion (type setting-pen) (r 100) (g 150) (b 0) (width 5))) +TUT> (defparameter *my-desig3(desig:a motion (type setting-pen) (r 100) (g 150) (b 0) (width 5))) 
-MY-DESIG3 +*MY-DESIG3* 
-TUT> (reference my-desig3)+TUT> (reference *my-desig3*)
 (SET-PEN #S(PEN-MOTION :R 100 :G 150 :B 0 :WIDTH 5 :OFF 0)) (SET-PEN #S(PEN-MOTION :R 100 :G 150 :B 0 :WIDTH 5 :OFF 0))
 </code> </code>