Delphi VCL components for GPS Communication and Coordinate Conversion
(Delphi 4 and 5)

Release 1.1, ©ScaryShed Software 2001

email : support@scaryshed.com  web : http://www.scaryshed.com

Package Contents:
TGPSPosition
TNMEA
TDatumChange
TEllip2Grid

Introduction

This component suite consists of two GPS communication components and two components to perform coordinate conversion calculations:

TGrmnPosition - communicate with a GPS receiver using Garmin's proprietary communication protocol

TNMEA - communicate with a GPS receiver using the widely supported NMEA-0183 protocol to determine position, speed, bearing and satellite availability

TDat2Dat - datum conversion from one geodetic datum to another

TEllip2Grid - convert geodetic/geographic (latitude and longitude) to Transverse Mercator (Grid) coordinates

Installation

To install these components copy the files contained in the distrubution zip file to the following locations

• .BPL files (e.g. ssgps5.bpl and ssgps5rt.bpl) should be copied to your delphi\bin directory;
• all other files (.DCP, .DCU) copy to your delphi\lib directory.  Alternatively, these files can be copied to any directory of your choice, providing the path is added to your Delphi search path;
• from within Delphi, select Install Packages from the Component menu.  Click Add, then select the ssGPS.bpl package from your delphi\bin directory.

Registration

Registration of this product will remove all the nag screens that periodically occur on component creation (at both design and run-time).  Registration costs £20 sterling.  To register, please visit our web page at www.scaryshed.com

Your attention is also drawn to the disclaimer at the end of this document. 

TGrmnPosition 

Downloads the current position from a Garmin GPS via the Garmin serial protocol.  The Garmin protocol operates on a request/response principle, therefore before reading Latitude and Longitude, there must be a call to GetData.

Properties

TGrmnPosition.Port

property Port : integer;

Set this property to specify the serial port  to which the GPS unit is connected.  Default value is 1 (COM1).

TGrmnPosition.Latitude

property Latitude : double;

Current GPS latitude in decimal degrees. Datum used is determined by the GPS unit. 

TGrmnPosition.Longitude

property Longitude : double;

Current GPS longitude in decimal degrees. Datum used is determined by the GPS unit. 

Methods

TGrmnPosition.OpenPort

function OpenPort : integer 

Opens the serial port specified by the Port property.  Call this function before using the GetData function to read from the GPS receiver. Function returns 1 if port opened successfully, 0 otherwise 

TGrmnPosition.ClosePort

function ClosePort : integer 

Closes the serial port currently in use Returns 1 if port closed successfully, 0 otherwise 

TGrmnPosition.GetData

function GetData : integer 

Causes the current GPS position to be downloaded and the component's Latitude and Longitude properties to be updated Returns 1 if successful, 0 otherwise 

TNMEA

The TNMEA component provides an interface to any GPS receiver implementing the NMEA-0183 protocol.  This protocol specifies that data should be transmitted in the form of "sentences" from the GPS device (the "talker") to the "listeners".  This makes the TNMEA component particularly easy to use, as there is no requirement on the listener to request data from the GPS device.  Once the com port is opened, all that is required is to respond to the events corresponding to the receipt of the different sentences.

Properties

TNMEA.OnPosition

property OnPosition : TNotifyEvent;

Event is fired when the NMEA message GGA ("Global positioning system fix data")  is received.  On receipt of this message from the GPS device, the contents are parsed into the GPSFix property before this event is fired.

TNMEA.OnSatelliteData 

property OnSatelliteData : TNotifyEvent;

Event is fired when the NMEA message GSV ("Satellites in view") is received.  On receipt of this message from the GPS device, the contents are parsed into the GPSSatellites property before this event is fired.

TNMEA.OnTransit 

property OnTransit : TNotifyEvent;

Event is fired when the NMEA message RMC ("Recommended minimum specific GPS/transit data") is received.  On receipt of this message from the GPS device, the contents are parsed into the GPSTransit property before this event is fired

TNMEA.OnError 

property OnError : TNotifyEvent;

Event is fired when an error occurs in processing an incoming NMEA string

TNMEA.ComPort 

property ComPort : byte;

Com port number that the GPS receiver is connected to.  Set this to the required value before calling the TNMEA.Open.

TNMEA.BaudRate 

property BaudRate : TBaudRate;

Baud rate for the com port the receiver is connected to.  Must match the baud rate set on the GPS device.  Default value 4800.

TNMEA.GPSFix 

property GPSFix : TGPSFix;

Hold the result of a successful decoding of a GGA message sent by the GPS device. This property is set immediately prior to the firing of the TNMEA.OnPosition event. 

TGPSFix = record
    UTCTime        : TTime;
    Latitude       : double;
    Longitude      : double;
    Quality        : integer;
    SatelliteCount : integer;
    Altitude       : single;
end;

Parameter	Meaning
UTCTime	Time the position was obtained
Latitude	Current Latitude
Longitude	Current longitude
Quality	Quality of the position fix 0=invalid; 1=GPS Fix; 2=DGPS Fix
SatelliteCount	Number of satellites being tracked
Altitude	Current altitude in metres above mean sea level

TNMEA.GPSTransit 

property GPSTransit : TGPSTransit;

Hold the result of a successful decoding of a RMC message sent by the GPS device. This property is set immediately prior to the firing of the TNMEA.OnTransit event and gives details of the current position, speed and bearing of the receiver.

TGPSTransit = record
    UTCDateTime       : TTime;
    Warning           : boolean;
    Latitude          : double;
    Longitude         : double;
    Speed             : single;
    Course            : single;
    MagneticVariation : single;
end;

Parameter	Meaning
UTCDateTime	Date and time message of fix
Warning	Navigation receiver warning, true if the fix is invalid
Latitude	Current latitude
Longitude	Current longitude
Speed	Speed over ground (in miles per hour)
Course	Course made good
MagneticVariation	Magnetic variation

 

TNMEA.GPSSatellites 

property GPSSatellites : TGPSSatellites;

Gives the result of a decoded GSV message (satellite data).  This property is set immediately prior to the firing of the TNMEA.OnSatellite event and gives details of the number of satellites in view, and their position.

TGPSSatellites = record
    SatelliteCount : integer;
    SatelliteData : array [1..12] of TSatellite;
end;

Parameter	Meaning
SatelliteCount	Number of satellites currently in view
SatelliteData	Array of satellite data.  Relevant data is held in SatelliteData[1..SatelliteCount]

TSatellite = record
    SatelliteID : integer;
    Elevation : integer;
    Azimuth : integer;
    Signal : integer;
end;

Parameter	Meaning
SatelliteID	Satellite PRN number
Elevation	Elevation in degrees
Azimuth	Azimuthal angle in degrees
Signal	Signal strength

Methods

TNMEA.Open 

function Open : boolean;

Opens the communication port and starts processing incoming data.  Note that, unlike the Garmin protocol used in the TGRMNPosition component, the NMEA protocol requires that the GPS device continually sends out position information.  Therefore, the only action required to receive data is to open the com port and process incoming data.

TNMEA.close 

function close : integer;

Cease processing incoming data and close the com port.

TEllip2Grid 

Converts Latitude and Longitude to Transverse Mercator (Grid) coordinates, and vice versa.

Properties

TEllip2Grid.Action

property Action : TAction;

Determines whether the Evaluate procedure performs an Ellipsoid to Grid conversion or vice versa

type  TAction = (EllipsToGrid,GridToEllips);

Value	Meaning
EllipsToGrid	Calling TEllip2Grid.Evaluate will convert elliptical to grid coordinates
GridToEllips	Calling TEllip2Grid.Evaluate will convert grid to elliptical coordinates

TEllip2Grid.Grid

property Grid : TGrid;

Grid to use in conversion

TEllip2Grid.Latitude

property Latitude : double

Ellipsoidal coordinate. To convert these to grid coordinates, set the Action property to EllipsToGrid, and call the Evaluate method

TEllip2Grid.Longitude

property Longitude : double

Ellipsoidal coordinate. To convert these to grid coordinates, set the Action property to EllipsToGrid, and call the Evaluate method

TEllip2Grid.Easting

property Easting : integer

Coordinates relative to the specified Grid.  To convert these to ellipsiodal coordinates, set the Action property to GridToEllips, and call the Evaluate method.

TEllip2Grid.Northing

property Northing : integer

Coordinates relative to the specified Grid.  To convert these to ellipsiodal coordinates, set the Action property to GridToEllips, and call the Evaluate method.

Methods

TEllip2Grid.Evaluate

procedure Evaluate;

Carries out the required conversion according to the current setting of the Action property.

TDatumChange 

Component converts Latitude and Longitude from one map datum to another by means of the Molodensky transformation

properties

TDatumChange.SourceDatum

property SourceDatum : TDatum;

Defines the datum for InputLatitude and InputLongitude

TDatumChange.TargetDatum

property TargetDatum : TDatum;

Defines the datum for OutputLatitude and OutputLongitude

TDatumChange.InputLatitude

property InputLatitude : double;

Source data for the conversion

TDatumChange.InputLongitude

property InputLongitude : double;

Source data for the conversion

TDatumChange.OutputLatitude

property OutputLatitude : double;

Results of the conversion

TDatumChange.OutputLongitude

property OutputLongitude : double;

Results of the conversion

Methods

TDatumChange.evaluate

procedure evaluate : double;

Performs the conversion from SourceDatum to TargetDatum

TGrid 

Properties

TGrid.GridName

property GridName : TGridName;

type TGridName = (grGB, grIrish, grUTM29, grUTM30, grUTM31, grUser);

Five pre-defined grids are available, plus one user specified. TGrid.  Other properties of TGrid are read-only, unless Grid.GridName = grUser.

Supplied grids are those relevant to the UK although, through the use of grUser, any grid can be defined.  The parameters for the five pre-defined grids are listed here.

Value	Meaning
grGB	OS GB National Grid
grIrish	Irish National Grid
grUTM29	UTM Zone 29
grUTM30	UTM Zone 30
grUTM31	UTM Zone 31
grUser	User-specified grid

TGrid.Ellipsoid

property Ellipsoid  : TEllipsoid;

The ellipsoid used for the projection.

TGrid.OriginLat

property OriginLat  : Double; 

Latitude of the true origin of the grid

TGrid.OriginLong

property OriginLong  : Double;

Longitude of the true origin of the grid

TGrid.OriginEast

property OriginEast  : integer;

Map coordinate (Easting) of the true origin, E₀

TGrid.OriginNorth

property OriginNorth : integer;

Map coordinate (Northing) of the true origin, N₀

TGrid.ScaleFactor

property ScaleFactor : double;

Scale factor on the central meridian, F₀

TEllipsoid

Properties

TEllipsoid.Name 

type TEllipsoidName = (elAiry30,elAiryMod,elAustNat,elBess41,elBess41Namib,elClarke66,
elClarke80,elEver30,elEverMod,elFisch60,elFisch60Mod,elFisch68,
elGRS67,elGRS75,elGRS80,elHough56,elInter,elKrass40,
elSAm69,elWGS60,elWGS66,elWGS72,elWGS84);

property Name : TEllipsoidName;

Selects an ellipsoid from the list of 23 pre-defined ellipsoids.

TEllipsoid.FullName

property FullName : string;

The full name of the ellipsoid.

TEllipsoid.a

property a : double;

Ellipsoid semi-major axis, a (in metres).

TEllipsoid.b

property b : double; 

Ellipsoid semi-minor axis, b (in metres).  b can be derived from the parameters a and f by the formula  b = a * (1 - f)

TEllipsoid.f_recip

property f_recip : double;

The reciprocal of the ellipsoid flattening parameter, f.

TDatum

Properties

TDatum.Name

Short name for the datum

property Name : TDatumName;

type TDatumName = (dtAdin,dtAEA,dtAfgo,dtAnAst,dtARC50,dtARC60,
dtAscI58,dtAst52,dtAstB4,dtAstBeacE,dtAstDos714,dtAust84,
dtBelleIGN,dtBerm57,dtBogObs,dtCampInch,dtCantAst,dtCape,
dtCapeCan,dtCart,dtCH03,dtChat71,dtChuAst,dtCorrAleg,
dtCypr,dtDjakBat,dtDOS68,dtEastIsl67,dtEuro50,dtEuro79,dtFin,
dtGandBase,dtGeoDat49,dtGuam63,dtGunSer62,dtGUX1Ast,dtHjor55,
dtHK63,dtHTS,dtIndia,dtIre65,dtISTS73Ast,dtJohnIsl,
dtKergIsl,dtKert48,dtLC5Ast,dtLib64,dtLuz,dtMah71,
dtMarcAst,dtMass,dtMerch,dtMidAst61,dtMinn,dtNAD27,
dtNAD27Alas{,dtNAD27Alas},dtNAD27Bah,dtNAD27Cub,
dtNAD27Green,dtNAD83,dtNahr,dtNapBWI,dtObs66,dtOldHawa,
dtOman,dtOSGB,dtPico,dtPitc67,dtPSthAm56,dtPSthChi63,dtPuerto,
dtQatar,dtQorn,dtRome40,dtSAD69Br,dtSanDOS,dtSap43,dtSchw,
dtSEBase,dtSthAm69,dtSthAs,dtSWBase,dtThai,dtTimb48,
dtTokyo,dtTrist68,dtVitiLev16,dtWake60,dtWGS72,dtWGS84,
dtZand);

TDatum.FullName 

property FullName : string 

Full name of the datum.

TDatum.Ellipsoid 

property Ellipsoid : TEllipsoid 

Ellipsoid used for this datum.

TDatum.dx 

 property dx : single 

Datum offset x

TDatum.dy

property dy : single 

Datum offset y

TDatum.dz

property dz : single 

Datum offset z

Change History

D I S C L A I M E R

Use of the components supplied as part of this package is entirely at the user's own risk. The author disclaims all warranties, expressed or implied, including, without limitation, the warranties of merchantability and of fitness for any purpose. The author assumes no liability for damages, direct or consequential, which may result from the use of these components.