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This page was last modified 04:28, 2 May 2008.

Bluetooth GPS 受信機 - NMEA解析

From Forum Nokia Wiki

英語版:Bluetooth GPS Receiver - NMEA Parsing

訳注: S60 3rd Edtion に関しては、S60 3rd Edition でのGPS API を参照

1 概論
2 前提条件
3 NMEAParser.h
4 NMEAParser.cpp
5 messageclient.h
6 messageclient.cpp
7 関連リンク

概論

携帯端末上の多くの位置情報サービスのアプリケーションは、頻繁にGPSのデータを取得します。S60端末では、緯度、http://ja.wikipedia.org/wiki/%E7%B5%8C%E5%BA%A6 経度]、http://ja.wikipedia.org/wiki/%E9%AB%98%E5%BA%A6 高度]、速度等のGPS詳細情報を取得出来ます。GPS受信機は、一般に、NMEA文で書かれたGPSデータを読みます。このNMEA文からGPS詳細情報を取得するのは、簡単には出来ません。GPS詳細情報を得るには、NMEAA文を解析する必要があります。Bluetooth GPS受信機に繋がったSymbian C++でどのようにしてNMEA文を解析するかを、以下のコードの断片は示します。

前提条件

Bluetooth GPS受信機
Bluetooth機能を使うために、SDKパッケージにあるbtpointtopoint を使います。
S60 2nd Editioin 端末

NMEAParser.h

#ifndef __CNMEAParser_H__
#define __CNMEAParser_H__
 
#include <E32Base.h>
 
class CNMEAParser : public CBase 
{
public:
 
	// Set the NMEA Data
	void SetData( TDesC8 & aNmeaMessage );
 
	// Skip the next Token from NMEA sentence
	void SkipNextTokenL( );
 
	// Read the Next Token from NMEA sentence
	void ReadNextTokenL( TDes8 & aBuffer );
 
	// Read Next Token from NMEA sentecne as Latitude
	TReal ReadNextTokenAsLatitudeL( );
 
	// Read Next Token from NMEA sentecne as Longitude
	TReal ReadNextTokenAsLongitudeL( );
 
	// This will return Next Token from NMEA sentence as TInt
	TInt ReadNextTokenAsIntL( );
 
	// This will return Next Token from NMEA sentence as TReal
	TReal ReadNextTokenAsRealL( );
 
	// Clear the NMEA Data
	void ClearData( );
 
 
private:
 
	TDesC8 * iMessage;
 
	TInt iParsePosition;
 
};
 
#endif

NMEAParser.cpp

#include <E32Math.h>
#include "NMEAParser.h"
 
// Set the NMEA Data
void CNMEAParser::SetData( TDesC8 & aNmeaMessage ) 
{
	iMessage = &aNmeaMessage;
	iParsePosition = 0;
}
 
 
// Read the Next Token from NMEA sentence
void CNMEAParser::ReadNextTokenL( TDes8 & aBuffer ) 
{
	if ( iMessage == NULL )
		User::Leave( KErrNotReady );
 
	if ( iParsePosition >= iMessage->Length( ) )
		return;
 
	while ( iParsePosition < iMessage->Length( ) ) 
	{
		TUint8 nextChar = ( *iMessage )[ iParsePosition++ ];
		if ( nextChar == ',' )
			break;
		aBuffer.Append( nextChar );
	}
 
}
 
 
// Skip the next Token from NMEA sentence
void CNMEAParser::SkipNextTokenL( ) 
{
 
	if ( iMessage == NULL )
		User::Leave( KErrNotReady );
 
	if ( iParsePosition >= iMessage->Length( ) )
		return;
 
	while ( iParsePosition < iMessage->Length( ) ) 
	{
		TUint8 nextChar = ( *iMessage )[ iParsePosition++ ];
		if ( nextChar == ',' )
			break;
	}
}
 
 
// Read Next Token from NMEA sentecne as Latitude
TReal CNMEAParser::ReadNextTokenAsLatitudeL( ) 
{
	TReal angle;
 
	TBuf8< 15 > angleString;
	ReadNextTokenL( angleString );
 
	TBuf8< 5 > northSouth;
	ReadNextTokenL( northSouth );
 
	TLex8 latLexer( angleString );
	TInt error = latLexer.Val( angle, '.' );
 
	if ( error != KErrNone )
		return 0.0;
	
 
	TInt32 degrees;
	Math::Int( degrees, angle / 100.0 );
 
	TInt32 minutes;
	Math::Int( minutes, angle - degrees * 100 );
 
	TReal decimal;
	Math::Frac( decimal, angle );
 
	TReal latitude = degrees + ( minutes + decimal ) / 60.0;
 
	if ( northSouth[ 0 ] == 'S' )
		latitude = -latitude;
 
	return( latitude );
}
 
 
// Read Next Token from NMEA sentecne as Longitude
TReal CNMEAParser::ReadNextTokenAsLongitudeL( ) 
{
	TReal angle;
 
	TBuf8< 15 > angleString;
	ReadNextTokenL( angleString );
 
	TBuf8< 5 > northSouth;
	ReadNextTokenL( northSouth );
 
	TLex8 latLexer( angleString );
	TInt error = latLexer.Val( angle, '.' );
 
	if ( error != KErrNone )
		return 0.0;
 
 
	TInt32 degrees;
	Math::Int( degrees, angle / 100.0 );
 
	TInt32 minutes;
	Math::Int( minutes, angle - degrees * 100 );
 
	TReal decimal;
	Math::Frac( decimal, angle );
 
	TReal longitude = degrees + ( minutes + decimal ) / 60.0;
 
	if ( northSouth[ 0 ] == 'W' )
		longitude = -longitude;
 
	return( longitude );
 
}
 
 
// This will return Next Token from NMEA sentence as TInt
TInt CNMEAParser::ReadNextTokenAsIntL( ) 
{
	TInt result = 0;
 
	TBuf8< 10 > intString;
	ReadNextTokenL( intString );
 
	TLex8 lexer( intString );
 
	TInt ret = lexer.Val( result );
	if( ret == KErrNone)
		return( result );
	else
		return 0.0;
 
}
 
 
// This will return Next Token from NMEA sentence as TReal
TReal CNMEAParser::ReadNextTokenAsRealL( ) 
{
	TReal result = 0;
 
	TBuf8< 10 > realString;
	ReadNextTokenL( realString );
 
	TLex8 lexer( realString );
	TInt ret = lexer.Val( result );
	if( ret == KErrNone)
		return( result );
	else
		return 0.0;
}
 
 
// Clear the NMEA Data
void CNMEAParser::ClearData( ) 
{
	iMessage = NULL;
	iParsePosition = 0;
}

messageclient.h

messageclient.h は、SDKパッケージ内のbtpointtopoint example にあります。
messageclient.h で、NMEAParser.h をインクルードしてください。

#include "NMEAParser.h" //For NMEA sentence Parsing

次の関数リストを宣言してください:

//Following functions are declared for NMEA sentence parsing purpose
public:
	void WriteToFile(TBuf8<100> aData);
	void NMEAUpdate( const TDes8 & aNMEABuffer );
 
	void HandleMessageL( TDesC8 & aCommand );
	void HandleGPGGAMsgL( TDesC8 & aCommand );
	void HandleGPGLLMsgL( TDesC8 & aCommand );
	void HandleGPVTGMsgL( TDesC8 & aCommand );
	void HandleGPRMCMsgL( TDesC8 & aCommand );

次の変数とオブジェクトのリストを宣言してください。

TBuf8 <1024>  iDummyBuffer
	TBuf8 <1024>  iTempBuffer;
	TBuf8 <256>	 iFileData;
	TBuf8 <512> iMessageBuffer;
	TReal speedInKMH;
 
	CNMEAParser iNmeaParser;

messageclient.cpp

EConnceted ケースを次のように変更してください:

case EConnected:
	iTempBuffer.Zero();
	iTempBuffer.Copy(iDummyBuffer);
	if( iTempBuffer.Length() > 200 )
		NMEAUpdate(iTempBuffer);
	// Just dump data
	iDummyBuffer.Zero();
	// Catch disconnection event 
	// By waiting to read socket
	WaitOnConnectionL();
	break;

NMEA文を処理する関数を実装します:

//Following functions are implemeted for NMEA sentence parsing purpose 
void CMessageClient::NMEAUpdate( const TDes8 & aNMEABuffer ) 
{
 
	TBool inMessage = ( iMessageBuffer.Length( ) > 0 ) ? ETrue : EFalse;
 
	for ( TInt Index = 0; Index < aNMEABuffer.Length( ); Index++ ) 
	{
		TUint8 next = aNMEABuffer[ Index ];
		if ( inMessage == EFalse && ( next == '$' ) )
			inMessage = ETrue;
 
		if ( inMessage )
			iMessageBuffer.Append( aNMEABuffer[ Index ] );
 
		if ( inMessage && ( next == 13 ) ) 
		{
			inMessage = EFalse;
			HandleMessageL( iMessageBuffer );
			iMessageBuffer.SetLength( 0 );
		}
	}
}

void CMessageClient::HandleMessageL( TDesC8 & aCommand ) 
{
	TBuf8< 32 > temp;
 
	_LIT( KGlobalPositioning, "$GPGGA" );
	temp.Copy( KGlobalPositioning );
 
	TInt foundGPGGA = aCommand.Find( temp );
	if ( foundGPGGA == 0 )
		HandleGPGGAMsgL( aCommand );
 
	_LIT( KGeographicPosition, "$GPGLL" );
	temp.Copy( KGeographicPosition );
 
	TInt foundGPGLL = aCommand.Find( temp );
	if ( foundGPGLL == 0 )
		HandleGPGLLMsgL( aCommand );
 
	_LIT( KCourseData, "$GPVTG" );
	temp.Copy( KCourseData );
 
	TInt foundGPVTG = aCommand.Find( temp );
	if ( foundGPVTG == 0 )
		HandleGPVTGMsgL( aCommand );
}

void CMessageClient::HandleGPGGAMsgL( TDesC8 & aCommand ) 
{
 
	iNmeaParser.SetData( aCommand );
	iNmeaParser.SkipNextTokenL( );	// skip message id
 
 
	TReal utcTime = iNmeaParser.ReadNextTokenAsRealL( );
	TReal Latitude = iNmeaParser.ReadNextTokenAsLatitudeL( );
	TReal Longitude = iNmeaParser.ReadNextTokenAsLongitudeL( );
	TInt fixValid = iNmeaParser.ReadNextTokenAsIntL( );
	TInt satellites = iNmeaParser.ReadNextTokenAsIntL( );
	TReal hdop = iNmeaParser.ReadNextTokenAsRealL( );
	TReal altitude = iNmeaParser.ReadNextTokenAsRealL( );
 
//Added for storing values in File 
	TBuf8<100> iData;
	iData.Format(_L8("Lat=%f\nLon=%f\nAlt=%f\n"),Latitude,Longitude,altitude);
	WriteToFile(iData);
//Code ends 
 
	iNmeaParser.ClearData( );
}

void CMessageClient::HandleGPGLLMsgL( TDesC8 & aCommand ) 
{
	iNmeaParser.SetData( aCommand );
	iNmeaParser.SkipNextTokenL( );	// skip message id
 
	TReal Latitude = iNmeaParser.ReadNextTokenAsLatitudeL( );
	TReal Longitude = iNmeaParser.ReadNextTokenAsLongitudeL( );
 
//Added for storing values in File 
	TBuf8<100> iData;
	iData.Format(_L8("Lat=%f Lon=%f\n"),Latitude,Longitude);
	WriteToFile(iData);
//Code ends
 
	iNmeaParser.ClearData( );
}

void CMessageClient::HandleGPVTGMsgL( TDesC8 & aCommand ) 
{
	iNmeaParser.SetData( aCommand );
	iNmeaParser.SkipNextTokenL( );	// skip message id
 
	TReal heading = iNmeaParser.ReadNextTokenAsRealL( );
	iNmeaParser.SkipNextTokenL( );	// skip heading unit
	iNmeaParser.SkipNextTokenL( );	// skip magnetic heading
	iNmeaParser.SkipNextTokenL( );	// skip magnetic heading unit
 
	TReal speedInKnots = iNmeaParser.ReadNextTokenAsRealL( );
 
//Convertion from speed in Knots into speed in KiloMeters/Hour
	speedInKMH = speedInKnots * 1.85 ;
//Conversion ends
 
	iNmeaParser.SkipNextTokenL( );	// skip speed unit
	iNmeaParser.SkipNextTokenL( );	// skip speed in km/h
	iNmeaParser.SkipNextTokenL( );	// skip speed unit
 
	iNmeaParser.ClearData( );
 
	//Added for storing values in File 
	TBuf8<100> iData;
	iData.Format(_L8("VTG Speed=%f\n"),speedInKMH);
	WriteToFile(iData);
//Code ends
}

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