tgherzog/00-resources.md

## 00-resources.md

      
    Raw
  

              00-resources.md
            
          
    NMEA Documentation

NMEA 0183 Specification
Fragmented evidence on depth sounder sentences:

This depth sounder display supports DBT, DPT, and PTTKD, whatever that is
This support ticket demonstrates some sample output

Scroll Views


Scroll View Tutorial with code in Github. Seems to do the trick, but code is in Objective C
Possibly this one - in Swift
This Youtube Video might do the trick
A Swift Scroll View video tutorial in 21 parts

C Interface

http://stackoverflow.com/questions/24146488/swift-pass-uninitialized-c-structure-to-imported-c-function
Customized Table Sections

http://www.ioscreator.com/tutorials/customizing-header-footer-table-view-ios8-swift
Today Widget


http://www.glimsoft.com/06/28/ios-8-today-extension-tutorial/
Shared Frameworks and Table Views
Sharing data via file system
convert class to NSData


## 01-swift-notes.md

      
    Raw
  

              01-swift-notes.md
            
          
    Using Optionals

Variable declarations
var foo:Int? // declare an optional value: use foo! to unwrap
var foo:Int! // implicitly unwrapped optional: foo! is not required

Class member access
var foo = bar?.bat // optional chaining: foo is nil if bar is nil
var foo = bar!.bat // runtime error if bar is nil

Casting
var foo as ClassName  // ordinary casting will fail for down casting
var foo as? ClassName // downcast to optional: return nil on failure
var foo as! ClassName // forced downcast: runtime error on failure

Function returns
func doSomething() -> Int { }    // ordinary return
func doSomething() -> Int? { }   // return optional
func doSomething() -> Int! { }   // return implicitly unwrapped value: not sure how this is useful

Exception Handling
var foo = try  funcThatThrows() // call a throwing function in the context of a do { }
var foo = try? funcThatThrows() // foo is nil if function throws an exception
var foo = try! funcThatThrows() // disable exception throwing when you know function will succeed


## nmea-server-emulator.php
<?php

/* Sets up a TCP or UDP broadcast process point that emulates the base unit of a sail timer wind vane

Supported arguments:

--port=port_number (default: 55554)
--input=data_file (default: sailtimer.txt)
--mode=1 - transmits data in randomly-sized blocks instead of complete nmea sentences (default: 0)
--type=tcp|udp - set socket type (default: udp)

Some resources:

http://www.ccplusplus.com/2011/09/udp-broadcast-client-server-example.html
http://www.tack.ch/multicast/broadcast.shtml
http://stackoverflow.com/questions/11135801/how-to-broadcast-message-using-udp-sockets-locally
https://www.google.com/#q=udp+broadcast+example+code

*/

$ip_address = getHostByName(getHostName());
$port = 55554;
$input_file = 'sailtimer.txt';
$mode = 0;
$ntype = 'udp';

$args = $argv;
array_shift($args);
while( substr($args[0],0,2) === '--' ) {
  list($key,$value) = explode('=', substr($args[0],2), 2);
  switch($key) {
    case 'port':
      $port = $value;
      break;
    case 'input':
      $input_file = $value;
      break;
    case 'type':
      $ntype = $value;
      break;
    case 'mode':
      $mode = $value;
      break;
  }

  array_shift($args);
}

if( $ntype == 'tcp' ) {
  print "Initiating $ntype connection at $ip_address on port $port\n";

  $socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
  if( $socket === false ) { die("socket_create failed.\n"); }

  if( socket_bind($socket, $ip_address, $port) === false ) {
    die("socket_bind() failed: " . socket_strerror(socket_last_error($socket)) . "\n");
  }

  if( socket_listen($socket, 5) === false ) {
    die("socket_listen() failed: " . socket_strerror(socket_last_error($socket)) . "\n");
  }

  if( ($socketConnection = socket_accept($socket)) === false ) {
    die("socket_accept() failed: " . socket_strerror(socket_last_error($socket)) . "\n");
  }

  socket_getpeername($socketConnection, $peerAddress);
  print "Connection accepted: $peerAddress\n";
}
elseif( $ntype == 'udp' ) {
  print "Initiating $ntype connection on port $port\n";

  $socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
  if( $socket === false ) { die("socket_create failed.\n"); }

  //Set socket options.
  socket_set_nonblock($socket);
  socket_set_option($socket, SOL_SOCKET, SO_BROADCAST, 1);
  socket_set_option($socket, SOL_SOCKET, SO_REUSEADDR, 1);
  if (defined('SO_REUSEPORT'))
      socket_set_option($socket, SOL_SOCKET, SO_REUSEPORT, 1);
}
else {
  die("Unknown connection type: $ntype\n");
}


//Bind to any address & port
/*
if(!socket_bind($socket, '127.0.0.1', 0))
    die("socket_bind failed.\n");
*/

$contents = file_get_contents($input_file);
$len = strlen($contents);
$m = 0;

// ping every 2 seconds
while( true ) {
  $msg = '';
  if( $mode == 0 ) {
    while( true ) {
      $i = substr($contents, $m, 1);
      $m++;
      $msg .= $i;
      if( $m == $len ) {
	$m = 0;
	break;
      }
      elseif( ord($i) == 0x0a ) break;
    }
  }
  else {
    $i = rand(1,32) + 8;
    $i = min($len - $m, $i);
    $msg = substr($contents, $m, $i);
    $m += $i;
    if( $len == $m ) $m = 0;
  }

  if( $ntype == 'tcp' ) {
    if( @socket_recv($socketConnection, $tmpBuffer, 1, MSG_PEEK|MSG_DONTWAIT) === false ) {
      $errorcode = socket_last_error($socketConnection);
      if( $errorcode != 35 ) {
	print "closing. error is $errorcode / " . socket_strerror($errorcode) . "\n";
	socket_close($socketConnection);
	break;
      }
    }

    socket_write($socketConnection, $msg, strlen($msg));
  }
  elseif( $ntype == 'udp' ) {
    socket_sendto($socket, $msg, strlen($msg), 0, '255.255.255.255', $port);
  }
  # print $msg;

  # sleep randomly, 0.5-2.0 seconds
  usleep((500 + rand(0,1500)) * 1000);
}

socket_close($socket);

/*
//Wait for data.
$read = array($socket); $write = NULL; $except = NULL;
while(socket_select($read, $write, $except, NULL)) {

    //Read received packets with a maximum size of 5120 bytes.
    while(is_string($data = socket_read($socket, 5120))) {
        echo $data;
    }

}
*/

## sailtimer.txt
$WIMWV,040.0,R,14.2,K,A*15
$SDDBT,53.4,f,16.3,M,8.9,F*37
$SDDPT,16.3,0.4*67
$WIMWV,049.0,R,09.7,K,A*15
$WIMWV,061.0,R,13.1,K,A*12
$WIBAT,1,7*4F
$SDDBT,55.4,f,16.9,M,9.2,F*35
$SDDPT,16.9,0.4*73
$WIMWV,061.0,R,14.1,K,A*15
$WIMWV,045.0,R,13.1,K,A*14
$SDDBT,54.2,f,16.5,M,9.0,F*42
$SDDPT,16.5,0.4*69
$WIMWV,064.0,R,12.9,K,A*1E
$WIMWV,055.0,R,12.7,K,A*12
$SDDBT,53.7,f,16.4,M,9.0,F*41
$SDDPT,16.4,0.4*68
$WIMWV,049.0,R,11.8,K,A*13
$WIMWV,049.0,R,10.5,K,A*1F
$SDDBT,53.5,f,16.3,M,8.9,F*36
$SDDPT,16.3,0.4*67
$WIMWV,032.0,R,09.0,K,A*1E
$WIMWV,029.0,R,09.3,K,A*17
$SDDBT,52.6,f,16.0,M,8.8,F*36
$SDDPT,16.0,0.4*64
$WIMWV,011.0,R,05.7,K,A*14
$SDDBT,50.0,f,15.2,M,8.3,F*42
$SDDPT,15.2,0.4*65
$WIMWV,030.0,R,06.1,K,A*12
$WIBAT,1,7*4F
$SDDBT,61.0,f,18.6,M,10.2,F*25
$SDDPT,18.6,0.4*72
$WIMWV,026.0,R,09.0,K,A*1B
$SDDBT,61.5,f,18.8,M,10.3,F*19
$SDDPT,18.8,0.4*70
$WIMWV,019.0,R,10.3,K,A*1C
$SDDBT,49.6,f,15.1,M,8.3,F*39
$SDDPT,15.1,0.4*66
$WIMWV,027.0,R,12.0,K,A*10
$SDDBT,52.9,f,16.1,M,8.8,F*42
$SDDPT,16.1,0.4*65
$WIMWV,030.0,R,13.9,K,A*1E
$SDDBT,55.1,f,16.8,M,9.2,F*39
$SDDPT,16.8,0.4*72
$WIMWV,029.0,R,12.1,K,A*1F
$SDDBT,58.2,f,17.7,M,9.7,F*34
$SDDPT,17.7,0.4*70
$WIMWV,013.0,R,16.6,K,A*15
$SDDBT,57.5,f,17.5,M,9.6,F*41
$SDDPT,17.5,0.4*68
$WIMWV,013.0,R,14.0,K,A*11
$SDDBT,54.3,f,16.6,M,9.0,F*40
$SDDPT,16.6,0.4*70
$WIMWV,040.0,R,16.6,K,A*13
$WIMWV,015.0,R,12.9,K,A*18
$WIBAT,1,7*4F
$SDDBT,51.4,f,15.7,M,8.6,F*47
$SDDPT,15.7,0.4*68
$WIMWV,042.0,R,13.3,K,A*11
$WIMWV,035.0,R,13.5,K,A*17
$WIMWV,033.0,R,08.9,K,A*17
$SDDBT,55.2,f,16.8,M,9.2,F*36
$SDDPT,16.8,0.4*72
$WIMWV,031.0,R,08.7,K,A*1B
$WIMWV,031.0,R,08.5,K,A*19
$SDDBT,61.4,f,18.7,M,10.2,F*28
$SDDPT,18.7,0.4*73
$WIMWV,039.0,R,11.3,K,A*1F
$WIMWV,015.0,R,12.4,K,A*15
$SDDBT,55.5,f,16.9,M,9.3,F*35
$SDDPT,16.9,0.4*73
$WIMWV,020.0,R,11.0,K,A*14
$WIMWV,016.0,R,09.0,K,A*18
$SDDBT,61.2,f,18.6,M,10.2,F*27
$SDDPT,18.6,0.4*72
$WIMWV,024.0,R,10.1,K,A*10
$WIBAT,1,7*4F
$WIMWV,022.0,R,09.1,K,A*1E
$SDDBT,55.0,f,16.8,M,9.2,F*38
$SDDPT,16.8,0.4*72
$WIMWV,018.0,R,13.5,K,A*18
$WIMWV,010.0,R,10.2,K,A*14
$SDDBT,53.1,f,16.2,M,8.9,F*33
$SDDPT,16.2,0.4*66
$WIMWV,027.0,R,11.5,K,A*16
$WIMWV,023.0,R,10.6,K,A*10
$SDDBT,53.3,f,16.2,M,8.9,F*35
$SDDPT,16.2,0.4*66
$WIMWV,026.0,R,13.2,K,A*12
$WIMWV,024.0,R,12.4,K,A*17
$SDDBT,56.8,f,17.3,M,9.5,F*32
$SDDPT,17.3,0.4*66
$WIMWV,024.0,R,13.9,K,A*1B
$WIMWV,016.0,R,12.6,K,A*14
$SDDBT,51.0,f,15.6,M,8.5,F*41
$SDDPT,15.6,0.4*69
$WIMWV,027.0,R,12.4,K,A*14

## truewind.php
<?php

function tws($awa,$aws,$cog,$sog) {


  $speed = $aws * $aws + $sog * $sog - 2.0 * $aws * $sog * cos( deg2rad($awa*$cog) );

  return sqrt( $speed );
}

function twa($awa, $aws, $cog, $sog) {

  $speed = tws($awa, $aws, $cog, $sog);

  if( $speed == 0 ) {
    return 0; // we're not moving
  }

  $angle = acos( ($aws * cos( deg2rad($awa)) - $sog) / $speed);

  if( $awa > 180 ) $angle *= -1;

  return rad2deg( $angle );
}

$args = $argv;
array_shift($args);

list($awa, $aws, $cog, $sog) = $args;

$angle = twa($awa, $aws, $cog, $sog);
$speed = tws($awa, $aws, $cog, $sog);

print <<<HERE
AWA: $awa
AWS: $aws
TWA: $angle
TWS: $speed
COG: $cog
SOG: $sog

HERE;

## truewind.swift
// Using these calculations: https://en.wikipedia.org/wiki/Apparent_wind
var trueWindSpeed:CLLocationSpeed? {

    if let course = self.course, aws = apparentWindSpeed, awa = apparentWindAngle, sog = self.speed {
      var speed:Double = aws*aws + sog*sog - 2.0*aws*sog * cos(deg2rad(degnormalize(awa+course)))

      return sqrt(speed)
    }

    return nil
}

var trueWindAngle:CLLocationDirection? {

    if let aws = apparentWindSpeed, awa = apparentWindAngle, sog = self.speed, tws = trueWindSpeed {

        // trap for div by 0
        if tws == 0.0 {
            return 0
        }

        var angle:Double = acos( (aws*cos(deg2rad(awa)) - sog) / tws)

        if awa > 180 {
            angle *= -1
        }

        return rad2deg(angle)
    }

    return nil
}

func deg2rad(degrees: CLLocationDirection) -> Double {
    return degrees * 3.14159 / 180.0
}

func rad2deg(rad: Double) -> CLLocationDirection {
    return round(rad * 180.0 / 3.14159)
}
	<?php

	/* Sets up a TCP or UDP broadcast process point that emulates the base unit of a sail timer wind vane

	Supported arguments:

	--port=port_number (default: 55554)
	--input=data_file (default: sailtimer.txt)
	--mode=1 - transmits data in randomly-sized blocks instead of complete nmea sentences (default: 0)
	--type=tcp\|udp - set socket type (default: udp)

	Some resources:

	http://www.ccplusplus.com/2011/09/udp-broadcast-client-server-example.html
	http://www.tack.ch/multicast/broadcast.shtml
	http://stackoverflow.com/questions/11135801/how-to-broadcast-message-using-udp-sockets-locally
	https://www.google.com/#q=udp+broadcast+example+code

	*/

	$ip_address = getHostByName(getHostName());
	$port = 55554;
	$input_file = 'sailtimer.txt';
	$mode = 0;
	$ntype = 'udp';

	$args = $argv;
	array_shift($args);
	while( substr($args[0],0,2) === '--' ) {
	list($key,$value) = explode('=', substr($args[0],2), 2);
	switch($key) {
	case 'port':
	$port = $value;
	break;
	case 'input':
	$input_file = $value;
	break;
	case 'type':
	$ntype = $value;
	break;
	case 'mode':
	$mode = $value;
	break;
	}

	array_shift($args);
	}

	if( $ntype == 'tcp' ) {
	print "Initiating $ntype connection at $ip_address on port $port\n";

	$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
	if( $socket === false ) { die("socket_create failed.\n"); }

	if( socket_bind($socket, $ip_address, $port) === false ) {
	die("socket_bind() failed: " . socket_strerror(socket_last_error($socket)) . "\n");
	}

	if( socket_listen($socket, 5) === false ) {
	die("socket_listen() failed: " . socket_strerror(socket_last_error($socket)) . "\n");
	}

	if( ($socketConnection = socket_accept($socket)) === false ) {
	die("socket_accept() failed: " . socket_strerror(socket_last_error($socket)) . "\n");
	}

	socket_getpeername($socketConnection, $peerAddress);
	print "Connection accepted: $peerAddress\n";
	}
	elseif( $ntype == 'udp' ) {
	print "Initiating $ntype connection on port $port\n";

	$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
	if( $socket === false ) { die("socket_create failed.\n"); }

	//Set socket options.
	socket_set_nonblock($socket);
	socket_set_option($socket, SOL_SOCKET, SO_BROADCAST, 1);
	socket_set_option($socket, SOL_SOCKET, SO_REUSEADDR, 1);
	if (defined('SO_REUSEPORT'))
	socket_set_option($socket, SOL_SOCKET, SO_REUSEPORT, 1);
	}
	else {
	die("Unknown connection type: $ntype\n");
	}


	//Bind to any address & port
	/*
	if(!socket_bind($socket, '127.0.0.1', 0))
	die("socket_bind failed.\n");
	*/

	$contents = file_get_contents($input_file);
	$len = strlen($contents);
	$m = 0;

	// ping every 2 seconds
	while( true ) {
	$msg = '';
	if( $mode == 0 ) {
	while( true ) {
	$i = substr($contents, $m, 1);
	$m++;
	$msg .= $i;
	if( $m == $len ) {
	$m = 0;
	break;
	}
	elseif( ord($i) == 0x0a ) break;
	}
	}
	else {
	$i = rand(1,32) + 8;
	$i = min($len - $m, $i);
	$msg = substr($contents, $m, $i);
	$m += $i;
	if( $len == $m ) $m = 0;
	}

	if( $ntype == 'tcp' ) {
	if( @socket_recv($socketConnection, $tmpBuffer, 1, MSG_PEEK\|MSG_DONTWAIT) === false ) {
	$errorcode = socket_last_error($socketConnection);
	if( $errorcode != 35 ) {
	print "closing. error is $errorcode / " . socket_strerror($errorcode) . "\n";
	socket_close($socketConnection);
	break;
	}
	}

	socket_write($socketConnection, $msg, strlen($msg));
	}
	elseif( $ntype == 'udp' ) {
	socket_sendto($socket, $msg, strlen($msg), 0, '255.255.255.255', $port);
	}
	# print $msg;

	# sleep randomly, 0.5-2.0 seconds
	usleep((500 + rand(0,1500)) * 1000);
	}

	socket_close($socket);

	/*
	//Wait for data.
	$read = array($socket); $write = NULL; $except = NULL;
	while(socket_select($read, $write, $except, NULL)) {

	//Read received packets with a maximum size of 5120 bytes.
	while(is_string($data = socket_read($socket, 5120))) {
	echo $data;
	}

	}
	*/
	$WIMWV,040.0,R,14.2,K,A*15
	$SDDBT,53.4,f,16.3,M,8.9,F*37
	$SDDPT,16.3,0.4*67
	$WIMWV,049.0,R,09.7,K,A*15
	$WIMWV,061.0,R,13.1,K,A*12
	$WIBAT,1,7*4F
	$SDDBT,55.4,f,16.9,M,9.2,F*35
	$SDDPT,16.9,0.4*73
	$WIMWV,061.0,R,14.1,K,A*15
	$WIMWV,045.0,R,13.1,K,A*14
	$SDDBT,54.2,f,16.5,M,9.0,F*42
	$SDDPT,16.5,0.4*69
	$WIMWV,064.0,R,12.9,K,A*1E
	$WIMWV,055.0,R,12.7,K,A*12
	$SDDBT,53.7,f,16.4,M,9.0,F*41
	$SDDPT,16.4,0.4*68
	$WIMWV,049.0,R,11.8,K,A*13
	$WIMWV,049.0,R,10.5,K,A*1F
	$SDDBT,53.5,f,16.3,M,8.9,F*36
	$SDDPT,16.3,0.4*67
	$WIMWV,032.0,R,09.0,K,A*1E
	$WIMWV,029.0,R,09.3,K,A*17
	$SDDBT,52.6,f,16.0,M,8.8,F*36
	$SDDPT,16.0,0.4*64
	$WIMWV,011.0,R,05.7,K,A*14
	$SDDBT,50.0,f,15.2,M,8.3,F*42
	$SDDPT,15.2,0.4*65
	$WIMWV,030.0,R,06.1,K,A*12
	$WIBAT,1,7*4F
	$SDDBT,61.0,f,18.6,M,10.2,F*25
	$SDDPT,18.6,0.4*72
	$WIMWV,026.0,R,09.0,K,A*1B
	$SDDBT,61.5,f,18.8,M,10.3,F*19
	$SDDPT,18.8,0.4*70
	$WIMWV,019.0,R,10.3,K,A*1C
	$SDDBT,49.6,f,15.1,M,8.3,F*39
	$SDDPT,15.1,0.4*66
	$WIMWV,027.0,R,12.0,K,A*10
	$SDDBT,52.9,f,16.1,M,8.8,F*42
	$SDDPT,16.1,0.4*65
	$WIMWV,030.0,R,13.9,K,A*1E
	$SDDBT,55.1,f,16.8,M,9.2,F*39
	$SDDPT,16.8,0.4*72
	$WIMWV,029.0,R,12.1,K,A*1F
	$SDDBT,58.2,f,17.7,M,9.7,F*34
	$SDDPT,17.7,0.4*70
	$WIMWV,013.0,R,16.6,K,A*15
	$SDDBT,57.5,f,17.5,M,9.6,F*41
	$SDDPT,17.5,0.4*68
	$WIMWV,013.0,R,14.0,K,A*11
	$SDDBT,54.3,f,16.6,M,9.0,F*40
	$SDDPT,16.6,0.4*70
	$WIMWV,040.0,R,16.6,K,A*13
	$WIMWV,015.0,R,12.9,K,A*18
	$WIBAT,1,7*4F
	$SDDBT,51.4,f,15.7,M,8.6,F*47
	$SDDPT,15.7,0.4*68
	$WIMWV,042.0,R,13.3,K,A*11
	$WIMWV,035.0,R,13.5,K,A*17
	$WIMWV,033.0,R,08.9,K,A*17
	$SDDBT,55.2,f,16.8,M,9.2,F*36
	$SDDPT,16.8,0.4*72
	$WIMWV,031.0,R,08.7,K,A*1B
	$WIMWV,031.0,R,08.5,K,A*19
	$SDDBT,61.4,f,18.7,M,10.2,F*28
	$SDDPT,18.7,0.4*73
	$WIMWV,039.0,R,11.3,K,A*1F
	$WIMWV,015.0,R,12.4,K,A*15
	$SDDBT,55.5,f,16.9,M,9.3,F*35
	$SDDPT,16.9,0.4*73
	$WIMWV,020.0,R,11.0,K,A*14
	$WIMWV,016.0,R,09.0,K,A*18
	$SDDBT,61.2,f,18.6,M,10.2,F*27
	$SDDPT,18.6,0.4*72
	$WIMWV,024.0,R,10.1,K,A*10
	$WIBAT,1,7*4F
	$WIMWV,022.0,R,09.1,K,A*1E
	$SDDBT,55.0,f,16.8,M,9.2,F*38
	$SDDPT,16.8,0.4*72
	$WIMWV,018.0,R,13.5,K,A*18
	$WIMWV,010.0,R,10.2,K,A*14
	$SDDBT,53.1,f,16.2,M,8.9,F*33
	$SDDPT,16.2,0.4*66
	$WIMWV,027.0,R,11.5,K,A*16
	$WIMWV,023.0,R,10.6,K,A*10
	$SDDBT,53.3,f,16.2,M,8.9,F*35
	$SDDPT,16.2,0.4*66
	$WIMWV,026.0,R,13.2,K,A*12
	$WIMWV,024.0,R,12.4,K,A*17
	$SDDBT,56.8,f,17.3,M,9.5,F*32
	$SDDPT,17.3,0.4*66
	$WIMWV,024.0,R,13.9,K,A*1B
	$WIMWV,016.0,R,12.6,K,A*14
	$SDDBT,51.0,f,15.6,M,8.5,F*41
	$SDDPT,15.6,0.4*69
	$WIMWV,027.0,R,12.4,K,A*14
	<?php

	function tws($awa,$aws,$cog,$sog) {


	$speed = $aws * $aws + $sog * $sog - 2.0 * $aws * $sog * cos( deg2rad($awa*$cog) );

	return sqrt( $speed );
	}

	function twa($awa, $aws, $cog, $sog) {

	$speed = tws($awa, $aws, $cog, $sog);

	if( $speed == 0 ) {
	return 0; // we're not moving
	}

	$angle = acos( ($aws * cos( deg2rad($awa)) - $sog) / $speed);

	if( $awa > 180 ) $angle *= -1;

	return rad2deg( $angle );
	}

	$args = $argv;
	array_shift($args);

	list($awa, $aws, $cog, $sog) = $args;

	$angle = twa($awa, $aws, $cog, $sog);
	$speed = tws($awa, $aws, $cog, $sog);

	print <<<HERE
	AWA: $awa
	AWS: $aws
	TWA: $angle
	TWS: $speed
	COG: $cog
	SOG: $sog

	HERE;
	// Using these calculations: https://en.wikipedia.org/wiki/Apparent_wind
	var trueWindSpeed:CLLocationSpeed? {

	if let course = self.course, aws = apparentWindSpeed, awa = apparentWindAngle, sog = self.speed {
	var speed:Double = awsaws + sogsog - 2.0awssog * cos(deg2rad(degnormalize(awa+course)))

	return sqrt(speed)
	}

	return nil
	}

	var trueWindAngle:CLLocationDirection? {

	if let aws = apparentWindSpeed, awa = apparentWindAngle, sog = self.speed, tws = trueWindSpeed {

	// trap for div by 0
	if tws == 0.0 {
	return 0
	}

	var angle:Double = acos( (aws*cos(deg2rad(awa)) - sog) / tws)

	if awa > 180 {
	angle *= -1
	}

	return rad2deg(angle)
	}

	return nil
	}

	func deg2rad(degrees: CLLocationDirection) -> Double {
	return degrees * 3.14159 / 180.0
	}

	func rad2deg(rad: Double) -> CLLocationDirection {
	return round(rad * 180.0 / 3.14159)
	}