GPSCom v1.06 / IConnectionPointImplMT v1.02

Welcome to GPSCom, a simple shareware COM based library which can be used to add GPS support to your Windows applications. GPSCom is a standard COM EXE developed in ATL in VC 2005 SP1. This component is intended as a complete replacement for the existing GPSLib DLL developed by the author. GPSCom internally uses an advanced ATL class called IConnectionPointImplMT. This module is licensed differently than GPSCom and is freeware, that is you are free to use it under the standard licensing conditions for my freeware source code. Please note that all the other modules inside of GPSCom are not open source.

Features

• Can be used by any development environment which supports calling an out of process COM object.
• Can be used by early or late bound clients i.e. COM development environments which do not use type libraries such as ASP, VBScript and JScript are fully compatible with GPSCom.
• Allows connections to GPS devices to be shared between multiple clients i.e. multiple client processes can share the one connection to the receivers serial port !!.
• A COM collection is provided to allow clients to enumerate existing connections which they can then connect to. This allows VB clients for example to use the "For Each" collection syntax.
• Alternatively, clients can open up a new connection and specify that the connection is not to be made sharable.
• COM Connection points are provided in the library to allow client apps to be notified in real time of incoming GPS NMEA sentences.
• Client apps can also poll the connection for the NMEA information if they so desire.
• Support for Unknown NMEA sentences.
• Supports any standard GPS device which supports the NMEA 0183 standard and which presents its data on a Windows Serial Port.

History

V1.0 (21 June 2002)

• Initial public release.

V1.01 (1 January 2003)

• Minor code tidy up.
• Now uses v1.15 of my Serial port class.

V1.02 (13 January 2004)

• Fixed a minor thread protection issue related to an internal variable used to signify that the worker thread which reads from the serial port should be shut down.
• Also fixed a few typos in the documentation (this file).

V1.03 (20 July 2006)

• Updated documentation to use the same style as the web site.
• Optimized CGPSConnection constructor code
• Optimized CGGASentence constructor code
• Code now uses new C++ style casts rather than old style C casts where necessary.
• Made code more robust by handling memory allocation failures.
• Optimized CRMCSentence constructor code.
• Updated the code to compile with v1.20 of the author's CSerialPort class.
• Optimized CGPSPort constructor code
• Reworked CNmeaSentence::Double implementation
• Replaced calls to ZeroMemory with memset
• Fixed bug in CNmeaSentence::Date to do with parsing of 2 digit years
• Removed unnecessary CRMCResponse destructor
• Updated code to clean compile on VC 2005

V1.04 GPSCom / v1.0 IConnectionPointImplMP (23 January 2007)

• Code is now built and delivered using VC 2005 SP1.
• Now uses v1.21 of the author's CSerialPort class.
• Fixed a bug in CRMCResponse::Parse where the m_IsDataValid was being set incorrectly. Thanks to "Kuronca" for reporting this problem.
• Complete review of the code in light of use of ATL8.
• Invalid RMC sentences are now also passed to clients.
• Removed the GGASentence::Valid property as it was not returning any useful information.
• The IConnectionPointImplMT class which GPSCom makes use of internally is being made available as freeware.

V1.05 GPSCom / v1.01 IConnectionPointImplMP (8 February 2008)

• Updated copyright details.
• GPSCom now internally uses v1.24 of CSerialPort.
• Fixed a bug in CGPSConnection::MonitorThread in the correct use of CT2A.
• How you implement the Fire_ methods as documented for IConnectionPointImplMP has been updated to refer to the need to serialize access to the "m_Clients" member variable which is accessed via the GetInterfaceAt method. The CProxy_IGPSConnectionEvents class in the GPSCom project and the IConnectionPointImplMT::GetInterfaceAt method have been updated to address this issue. Thanks to Michael Ford for reporting this bug.
• The actual pointers which are stored on the internal IConnectionPointImplMP::m_Clients array are now "CComGITPtr<TSinkInterface>" heap pointers rather than actual stack instances. By doing this, the code now has explicit control over when and how copy constructors and operator= methods are being called as we add a element to the array. This avoids extra overhead as the interface pointer is being added to the GIT. It also addresses an issue where the cookie value which was being returned by Advise was actually incorrect due to the fact that a copy of the CComGITPtr was being added to the array. Thanks to Michael Ford for reporting this issue.

V1.06 GPSCom / v1.02 IConnectionPointImplMP (21 March 2010)

• Updated copyright details.
• GPSCom now internally uses v1.27 of CSerialPort.

• Updated the instructions on how to code the Fire_* methods to avoid a COM reference counting problem which could have resulted in memory leaks. Thanks to Peter Blanz for reporting this issue.

Installation & Redistribution

The GPSCom EXE is a standard self-registering COM EXE so registration / un-registration is handled using the "/RegServer" or "/UnRegServer" command line parameters. If you are using a MSI based installer, then the recommended way to register the component is to avoid self registration and instead extract the registration details into the MSI tables.

The zip file comes with a ready to ship Unicode Release of GPSCom in the "Unicode Release" directory which will work on Windows NT 4 or later.

When it comes time to distribute your applications you will need to ship "GPSCom.exe" and the VC 2005 SP1 runtimes. if you are using the VS 2005 Bootstrapper then you can use the standard vcredist_x86 or vcredist_x64 prerequisites.

Usage

To start developing client applications using GPSCom, all you need to do is pull in the GPSCom library using whatever support your development environment provides for using COM objects. Please note that internally the code makes use of a COM mechanism called the "Global Interface Table" which is only available on Windows NT SP 3 or later or Windows 95 (or later) with DCOM version 1.1 or later installed.

To create a connection to a GPS device you can use the GPSConnections class which provides a standard COM collection of all the existing GPSConnections currently created. Alternatively use the GPSPort::CreateConnection method to create a new connection. The properties of the GPSPort decide how the serial port is to be opened. Using the default values will open the connection to the device thro COM1 with no Init String (Some GPS devices require a custom init string to get them to start sending data), 4800 baud, 8 data bits, 1 stop bit and no parity.

Once you have a GPSConnection object you can then either poll it's two main properties GGA and RMC which correspond to the latest NMEA sentences of this name.

The GGA sentence provides the distance above the WGS84 ellipsoid in metres, type of Fix obtained (enums are provided for this property as well as all other numeric enum values) and the Number of Satellites.

The RMC sentence provides the date and time of the fix, Latitude (as an integer value of hundreds of arc seconds and always positive), Longitude (again as an integer value of hundreds of arc seconds and always positive), Speed over the ground in knots and Compass Bearing from East of North. The Northing boolean properties indicates if the latitude is North or South of the Equator, while the Easting property indicates if the longitude is East or West of the Prime Meridian.

Included with the download is a very simple VB 6 app which exercises all of the functionality of the library. You should be able to get an idea on how to use the library by examining the code in this sample.

Shareware Notice

GPCom is shareware and this trial version is a fully functional evaluation copy. This means that you are free to evaluate GPSCom for up to 30 days. After this period if you are still using GPSCom and/or wish to include it in a project of yours, then you are legally obliged to register GPSCom with the author. Registration will entitle you to comprehensive email support from the author. The cost is $20 US dollars. I do not support online registration for this product yet so you must register via normal post. Remember to include your email address in your letter so that I can quickly confirm receipt of your registration. Payment should be made by cheque and be made out to:

The registration fee is very small and its a great incentive for me to keep improving GPSCom. Once I have received the registration you are entitled to unlimited email support for GPSCom.

Planned Enhancements

• Support more sentence types. Currently it slightly exceeds the functionality of the existing GPSLib SDK developed by the author.
• Rework the object model exposed to use a more efficient model to avoid multiple calls back to the COM server. This will entail denormalizing the object model and instead provide these values as additional parameter values in each method.
• Rework the serial port reading code to use the more efficient overlapped IO programming model.
• If you have any other suggested improvements for GPSCom, please let me know so that I can incorporate them into the next release of GPSCom.

Contacting the Author

PJ Naughter
Email: pjna@naughter.com
Web: http://www.naughter.com
21 March 2010