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Crumbtrail » Hydromagic » Hydrographic » GPS Receivers

GPS Receiver Devices

Eye4Software Hydromagic for Windows is a hydrographic survey software product. Using a GPS Receiver and an Echo Sounder it maps nautical areas into a map database and allows to you view and edit the maps, display positions and more.

GPS receiver communications are defined by the National Marine Electronics Association (NMEA) specifications. It defines how information should be sent and received by the devices. Computer software that deals wth real time maritime position expect the data to be in NMEA format. This data format includes the so called PVT - Postition, Velocity and Time. This PVT data is collected and calculated by the GPS receiver.

So, what's the idea behind NMEA? Well, it defines a standard line of data (called 'sentence') that is completely independent from other data or sentences. The other senteces may hold other standard information, or proprietary information. All standard GPS sentences are prefixed by two characters. For GPS receivers it is: 'GP'. All proprietary sentences start with a 'P' and are followed by three characters, indicating the manufacturer ID, e.g. Garmin starts with 'PGRM'.

After the prefix there's the '$' followed by the data. It ends with a carriage return/line and has a maximum length of 80 characters of text. The data contains data-items each separated by a comma. The data-item itself is ascii text. The precision of the data may vary. For example a time-stamp may hold full seconds or parts of seconds, and location may be show 2 or 3 decimals.

Eye4Software Hydromagic works with a wide variety of NMEA 0183 compatible GPS Receivers, including: