Delphi/Lazarus - GPS Bricklet

This is the description of the Delphi/Lazarus API bindings for the GPS Bricklet. General information and technical specifications for the GPS Bricklet are summarized in its hardware description.

An installation guide for the Delphi/Lazarus API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Simple

Download (ExampleSimple.pas)

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program ExampleSimple;

{$ifdef MSWINDOWS}{$apptype CONSOLE}{$endif}
{$ifdef FPC}{$mode OBJFPC}{$H+}{$endif}

uses
  SysUtils, IPConnection, BrickletGPS;

type
  TExample = class
  private
    ipcon: TIPConnection;
    gps: TBrickletGPS;
  public
    procedure Execute;
  end;

const
  HOST = 'localhost';
  PORT = 4223;
  UID = 'XYZ'; { Change XYZ to the UID of your GPS Bricklet }

var
  e: TExample;

procedure TExample.Execute;
var latitude, longitude: longword; ns, ew: char; pdop, hdop, vdop, epe: word;
begin
  { Create IP connection }
  ipcon := TIPConnection.Create;

  { Create device object }
  gps := TBrickletGPS.Create(UID, ipcon);

  { Connect to brickd }
  ipcon.Connect(HOST, PORT);
  { Don't use device before ipcon is connected }

  { Get current coordinates }
  gps.GetCoordinates(latitude, ns, longitude, ew, pdop, hdop, vdop, epe);

  WriteLn(Format('Latitude: %f °', [latitude/1000000.0]));
  WriteLn(Format('N/S: %s', [ns]));
  WriteLn(Format('Longitude: %f °', [longitude/1000000.0]));
  WriteLn(Format('E/W: %s', [ew]));

  WriteLn('Press key to exit');
  ReadLn;
  ipcon.Destroy; { Calls ipcon.Disconnect internally }
end;

begin
  e := TExample.Create;
  e.Execute;
  e.Destroy;
end.

Callback

Download (ExampleCallback.pas)

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program ExampleCallback;

{$ifdef MSWINDOWS}{$apptype CONSOLE}{$endif}
{$ifdef FPC}{$mode OBJFPC}{$H+}{$endif}

uses
  SysUtils, IPConnection, BrickletGPS;

type
  TExample = class
  private
    ipcon: TIPConnection;
    gps: TBrickletGPS;
  public
    procedure CoordinatesCB(sender: TBrickletGPS; const latitude: longword;
                            const ns: char; const longitude: longword; const ew: char;
                            const pdop: word; const hdop: word; const vdop: word;
                            const epe: word);
    procedure Execute;
  end;

const
  HOST = 'localhost';
  PORT = 4223;
  UID = 'XYZ'; { Change XYZ to the UID of your GPS Bricklet }

var
  e: TExample;

{ Callback procedure for coordinates callback }
procedure TExample.CoordinatesCB(sender: TBrickletGPS; const latitude: longword;
                                 const ns: char; const longitude: longword;
                                 const ew: char; const pdop: word; const hdop: word;
                                 const vdop: word; const epe: word);
begin
  WriteLn(Format('Latitude: %f °', [latitude/1000000.0]));
  WriteLn(Format('N/S: %s', [ns]));
  WriteLn(Format('Longitude: %f °', [longitude/1000000.0]));
  WriteLn(Format('E/W: %s', [ew]));
  WriteLn('');
end;

procedure TExample.Execute;
begin
  { Create IP connection }
  ipcon := TIPConnection.Create;

  { Create device object }
  gps := TBrickletGPS.Create(UID, ipcon);

  { Connect to brickd }
  ipcon.Connect(HOST, PORT);
  { Don't use device before ipcon is connected }

  { Register coordinates callback to procedure CoordinatesCB }
  gps.OnCoordinates := {$ifdef FPC}@{$endif}CoordinatesCB;

  { Set period for coordinates callback to 1s (1000ms)
    Note: The coordinates callback is only called every second
          if the coordinates has changed since the last call! }
  gps.SetCoordinatesCallbackPeriod(1000);

  WriteLn('Press key to exit');
  ReadLn;
  ipcon.Destroy; { Calls ipcon.Disconnect internally }
end;

begin
  e := TExample.Create;
  e.Execute;
  e.Destroy;
end.

API

Since Delphi does not support multiple return values directly, we use the out keyword to return multiple values from a function.

All functions and procedures listed below are thread-safe.

Basic Functions

constructor TBrickletGPS.Create(const uid: string; ipcon: TIPConnection)

Creates an object with the unique device ID uid:

gps := TBrickletGPS.Create('YOUR_DEVICE_UID', ipcon);

This object can then be used after the IP Connection is connected (see examples above).

procedure TBrickletGPS.GetCoordinates(out latitude: longword; out ns: char; out longitude: longword; out ew: char; out pdop: word; out hdop: word; out vdop: word; out epe: word)

Returns the GPS coordinates. Latitude and longitude are given in the DD.dddddd° format, the value 57123468 means 57.123468°. The parameter ns and ew are the cardinal directions for latitude and longitude. Possible values for ns and ew are 'N', 'S', 'E' and 'W' (north, south, east and west).

PDOP, HDOP and VDOP are the dilution of precision (DOP) values. They specify the additional multiplicative effect of GPS satellite geometry on GPS precision. See here for more information. The values are give in hundredths.

EPE is the "Estimated Position Error". The EPE is given in cm. This is not the absolute maximum error, it is the error with a specific confidence. See here for more information.

This data is only valid if there is currently a fix as indicated by GetStatus.

procedure TBrickletGPS.GetStatus(out fix: byte; out satellitesView: byte; out satellitesUsed: byte)

Returns the current fix status, the number of satellites that are in view and the number of satellites that are currently used.

Possible fix status values can be:

Value Description
1 No Fix, GetCoordinates, GetAltitude and GetMotion return invalid data
2 2D Fix, only GetCoordinates and GetMotion return valid data
3 3D Fix, GetCoordinates, GetAltitude and GetMotion return valid data

There is also a blue LED on the Bricklet that indicates the fix status.

The following constants are available for this function:

  • BRICKLET_GPS_FIX_NO_FIX = 1
  • BRICKLET_GPS_FIX_2D_FIX = 2
  • BRICKLET_GPS_FIX_3D_FIX = 3
procedure TBrickletGPS.GetAltitude(out altitude: longint; out geoidalSeparation: longint)

Returns the current altitude and corresponding geoidal separation.

Both values are given in cm.

This data is only valid if there is currently a fix as indicated by GetStatus.

procedure TBrickletGPS.GetMotion(out course: longword; out speed: longword)

Returns the current course and speed. Course is given in hundredths degree and speed is given in hundredths km/h. A course of 0° means the Bricklet is traveling north bound and 90° means it is traveling east bound.

Please note that this only returns useful values if an actual movement is present.

This data is only valid if there is currently a fix as indicated by GetStatus.

procedure TBrickletGPS.GetDateTime(out date: longword; out time: longword)

Returns the current date and time. The date is given in the format ddmmyy and the time is given in the format hhmmss.sss. For example, 140713 means 14.05.13 as date and 195923568 means 19:59:23.568 as time.

Advanced Functions

procedure TBrickletGPS.Restart(const restartType: byte)

Restarts the GPS Bricklet, the following restart types are available:

Value Description
0 Hot start (use all available data in the NV store)
1 Warm start (don't use ephemeris at restart)
2 Cold start (don't use time, position, almanacs and ephemeris at restart)
3 Factory reset (clear all system/user configurations at restart)

The following constants are available for this function:

  • BRICKLET_GPS_RESTART_TYPE_HOT_START = 0
  • BRICKLET_GPS_RESTART_TYPE_WARM_START = 1
  • BRICKLET_GPS_RESTART_TYPE_COLD_START = 2
  • BRICKLET_GPS_RESTART_TYPE_FACTORY_RESET = 3
function TBrickletGPS.GetAPIVersion: array [0..2] of byte

Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

function TBrickletGPS.GetResponseExpected(const functionId: byte): boolean

Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by SetResponseExpected. For setter functions it is disabled by default and can be enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

See SetResponseExpected for the list of function ID constants available for this function.

procedure TBrickletGPS.SetResponseExpected(const functionId: byte; const responseExpected: boolean)

Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

The following function ID constants are available for this function:

  • BRICKLET_GPS_FUNCTION_RESTART = 6
  • BRICKLET_GPS_FUNCTION_SET_COORDINATES_CALLBACK_PERIOD = 7
  • BRICKLET_GPS_FUNCTION_SET_STATUS_CALLBACK_PERIOD = 9
  • BRICKLET_GPS_FUNCTION_SET_ALTITUDE_CALLBACK_PERIOD = 11
  • BRICKLET_GPS_FUNCTION_SET_MOTION_CALLBACK_PERIOD = 13
  • BRICKLET_GPS_FUNCTION_SET_DATE_TIME_CALLBACK_PERIOD = 15
procedure TBrickletGPS.SetResponseExpectedAll(const responseExpected: boolean)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

procedure TBrickletGPS.GetIdentity(out uid: string; out connectedUid: string; out position: char; out hardwareVersion: array [0..2] of byte; out firmwareVersion: array [0..2] of byte; out deviceIdentifier: word)

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

procedure TBrickletGPS.SetCoordinatesCallbackPeriod(const period: longword)

Sets the period in ms with which the OnCoordinates callback is triggered periodically. A value of 0 turns the callback off.

The OnCoordinates callback is only triggered if the coordinates changed since the last triggering.

The default value is 0.

function TBrickletGPS.GetCoordinatesCallbackPeriod: longword

Returns the period as set by SetCoordinatesCallbackPeriod.

procedure TBrickletGPS.SetStatusCallbackPeriod(const period: longword)

Sets the period in ms with which the OnStatus callback is triggered periodically. A value of 0 turns the callback off.

The OnStatus callback is only triggered if the status changed since the last triggering.

The default value is 0.

function TBrickletGPS.GetStatusCallbackPeriod: longword

Returns the period as set by SetStatusCallbackPeriod.

procedure TBrickletGPS.SetAltitudeCallbackPeriod(const period: longword)

Sets the period in ms with which the OnAltitude callback is triggered periodically. A value of 0 turns the callback off.

The OnAltitude callback is only triggered if the altitude changed since the last triggering.

The default value is 0.

function TBrickletGPS.GetAltitudeCallbackPeriod: longword

Returns the period as set by SetAltitudeCallbackPeriod.

procedure TBrickletGPS.SetMotionCallbackPeriod(const period: longword)

Sets the period in ms with which the OnMotion callback is triggered periodically. A value of 0 turns the callback off.

The OnMotion callback is only triggered if the motion changed since the last triggering.

The default value is 0.

function TBrickletGPS.GetMotionCallbackPeriod: longword

Returns the period as set by SetMotionCallbackPeriod.

procedure TBrickletGPS.SetDateTimeCallbackPeriod(const period: longword)

Sets the period in ms with which the OnDateTime callback is triggered periodically. A value of 0 turns the callback off.

The OnDateTime callback is only triggered if the date or time changed since the last triggering.

The default value is 0.

function TBrickletGPS.GetDateTimeCallbackPeriod: longword

Returns the period as set by SetDateTimeCallbackPeriod.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done by assigning a procedure to an callback property of the device object:

procedure TExample.MyCallback(sender: TBrickletGPS; const param: word);
begin
  WriteLn(param);
end;

gps.OnExample := {$ifdef FPC}@{$endif}example.MyCallback;

The available callback property and their type of parameters are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

property TBrickletGPS.OnCoordinates
procedure(sender: TBrickletGPS; const latitude: longword; const ns: char; const longitude: longword; const ew: char; const pdop: word; const hdop: word; const vdop: word; const epe: word) of object;

This callback is triggered periodically with the period that is set by SetCoordinatesCallbackPeriod. The parameters are the same as for GetCoordinates.

The OnCoordinates callback is only triggered if the coordinates changed since the last triggering and if there is currently a fix as indicated by GetStatus.

property TBrickletGPS.OnStatus
procedure(sender: TBrickletGPS; const fix: byte; const satellitesView: byte; const satellitesUsed: byte) of object;

This callback is triggered periodically with the period that is set by SetStatusCallbackPeriod. The parameters are the same as for GetStatus.

The OnStatus callback is only triggered if the status changed since the last triggering.

The following constants are available for this function:

  • BRICKLET_GPS_FIX_NO_FIX = 1
  • BRICKLET_GPS_FIX_2D_FIX = 2
  • BRICKLET_GPS_FIX_3D_FIX = 3
property TBrickletGPS.OnAltitude
procedure(sender: TBrickletGPS; const altitude: longint; const geoidalSeparation: longint) of object;

This callback is triggered periodically with the period that is set by SetAltitudeCallbackPeriod. The parameters are the same as for GetAltitude.

The OnAltitude callback is only triggered if the altitude changed since the last triggering and if there is currently a fix as indicated by GetStatus.

property TBrickletGPS.OnMotion
procedure(sender: TBrickletGPS; const course: longword; const speed: longword) of object;

This callback is triggered periodically with the period that is set by SetMotionCallbackPeriod. The parameters are the same as for GetMotion.

The OnMotion callback is only triggered if the motion changed since the last triggering and if there is currently a fix as indicated by GetStatus.

property TBrickletGPS.OnDateTime
procedure(sender: TBrickletGPS; const date: longword; const time: longword) of object;

This callback is triggered periodically with the period that is set by SetDateTimeCallbackPeriod. The parameters are the same as for GetDateTime.

The OnDateTime callback is only triggered if the date or time changed since the last triggering.

Constants

const BRICKLET_GPS_DEVICE_IDENTIFIER

This constant is used to identify a GPS Bricklet.

The GetIdentity function and the TIPConnection.OnEnumerate callback of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.

const BRICKLET_GPS_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a GPS Bricklet.