Boatscript

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Auto-pilots are taboo in virtual regattas. People feel the game will loose if too much automation creeps in. Still there are times we wish boats had a little intelligence of their own.

Going hours with the wrong sail? Or getting stuck against the wind during the night? Can a Captn get some decent sleep???

Enter Boat Script. BS is a script system designed to facilitate monitoring and controlling boats [b]in vrtool[/b]. It uses JavaScript, a powerful and popular script language.

ScriptPouc1.png

Only vrtool's own sandbox boats can be controlled (course/sail). Other boats can be monitored. Scripts always run in the client machine. Running untrusted scripts (like web browsers do) is tricky.

The following illustrates a simple Boat Script:

function OnNewPosition() {
   Boat.Course = Boat.BCD;         
   Boat.Sail   = Boat.BestSail;
   Boat.Commit();
}

Event OnNewPosition() is fired when a new point is added to boat track (a 10 min tick)

What this script does?

 1- Sets boat course to the best course to destination (best velocity made good)
 2- Selects the best sail for that course
 3- Uses Commit() to send the control action to the server (if course and/or sail changed)

Only 5 lines, yet pretty efficient. It will even enter zig-zag mode as needed (see image below)

ZigZag15Apr11.jpg

The full BoatScript interface is below:

Control Parameters (read/write):

Boat.Course;            int
Boat.Sail;              int - Numeric sail ID
Boat.Commit();          Sends changed control parameters to server (if course or sail changed)

Boat data properties (read only):

Boat.Boatspeed;         double     in knts
Boat.Latitude;          double
Boat.Longitude;         double
Boat.TWS;               double     Wind speed in knts
Boat.TWD;               int        Wind direction
Boat.TWA;               int        Wind angle
Boat.Classif;           int        Classification
Boat.DestDirection;     int        Direction to destination
Boat.DestDistance;      double     Distance to destination in NM
Boat.BCD;               int        Best course to destination
Boat.VMC;               double     Velocity made good to destinatio
Boat.BestSail;          int        Best sail for the course
Boat.PosTime;           datetime   Position time
Boat.Boatname;          String     Boat name
Boat.Sailname;          String     Sail name

Query other boats:

Boat.BoatDistance(Boatname);    double  Distance to another boat in NM (returns 0 if boat not found)
Boat.BoatDirection(Boatname);   int     Direction to another boat (returns -1 if boat not found)
Boat.PointDistance(lat,lon);    double  Distance to a point in NM
Boat.PointDirection(lat,lon);   int     Direction to a point       
Boat.GetBoat(Boatname);         returns interface to another Boat (null if boat not found)
  You can use other boat data in your script, but cannot commit changes 
  to control parameters in other boats (of course).

Script logging:

Boat.ShowData();                Show boat data in script log
Boat.ShowMessage(Msg);          Show message in script log
Boat.ClearMessages();           Clear script log

Events:

function OnNewPosition() {
  //fired every time a new point is received
}

// the texts after two slashes are comments (not necessary to run the script) Notes:

  • All distances and directions calculated with great circle formulas
  • South latitudes and East longitudes are negative

Script examples:

corkscrew route:

// "corkscrew route" - boat script
// - increasing course regularly ( 2 degrees/10 min tick )
// - always use best sail (screw the crew)
// - skip pointing upwind

function OnNewPosition() {
   Boat.Course = Boat.Course+2;   // increase course each tick

   if (Boat.TWA<45) {             // skip upwind (wind angle<45)
     Boat.Course = Boat.Course+90;
     Boat.ShowMessage("Tack!");
     }

   Boat.Sail   = Boat.BestSail;     //change sail if needed

   //print information
   Boat.ShowData();
   Boat.ShowMessage("Hi Captn. Doing good at "+Boat.Boatspeed+" knts");
   Boat.Commit();         // sends control params, if changed
}
<pre>

Follow a boat (either local or VR)

<pre>
//  "bs_followTitanic.js" - Follows a boat named "Titanic" with best sail

function OnNewPosition() {
  var c = Boat.BoatDirection("Titanic");    // BoatDirection() returns -1 if boat not found  
  if (c>=0) {
    Boat.Course = c;    
	Boat.Sail = Boat.BestSail; 
	Boat.Commit();
  }
}

Print VMC table:

// "print VMC table" - boat script
// - this example prints a table with course;vmc columns
// - example of how to use the script log
// - does not affect boat control ( since there is no commit() command )

function OnNewPosition() {
   var bestSpeed=0;
   var bestCourse=0;
   var vmc;

   for (i=0; i<360; i++) {
      Boat.Course = i;
      vmc = Boat.VMC;
      if (vmc>bestSpeed) {
        bestSpeed=vmc;
        bestCourse=i;
      }
      Boat.ShowMessage(i+";"+vmc);
   }
   Boat.ShowMessage("best course="+bestCourse+"/best vmc="+bestSpeed);
}

Usage

Use BoatScript panel in Remote Boat control window, as illustrated below.

Important:Remember to save the script. I use files named bs_scriptname.js. Scripts are saved as external .js files, not embedded in the desktop. So any change must be saved to the script file to remain persistent.

ScriptPouc1.png