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Earthmate Software

Updated 0800 Friday 12th October 2007

Note from Robin in 2006: I've kept this page here for historical reasons. Good GPS receivers are now so inexpensive, it seems to me rather silly to mess about with non standard receivers and hardware or software to make them standard NMEA. However, I'm sure there are some of you who will have a reason for this, and not want to follow the simple advice on my GPS page :-)

The old DeLorme Tripmate GPS generates standard NMEA output, and can therefore be used with alternative GPS Software, including GPSS. The latest USB Earthmate also outputs NMEA and can be used with GPSS after editing GPSS.CFG to change COM1 to the correct port (e.g. COM3 - see "Problems?" on download page).

However, the early DeLorme Earthmate does NOT output NMEA and will therefore not work with GPSS. Earthmate generates Rockwell Protocol.

There are no plans to support Rockwell Protocol in GPSS, but there is an alternative: to use a small 'Driver Program' that reads the Rockwell Protocol data from the COM port, and converts this data to NMEA (e.g. the $GPRMC sentence) input to GPSS. - or a special hardware adapter.

Hardware Solution

You may want to checkout this Earthmate to NMEA Website which describes a neat bit of hardware that plugs between the Earthmate and PC, to convert the Rockwell binary stream into standard NMEA. It sells at about 47$US + 3$US for post and package.

Software Solution

from Robin in October 2007: mamy thanks to Joshua for emailing me the link users.tpg.com.au/adslobjm/ from which you can download eartha2nmea by Tooraj. See below.

Martin Grossman has already written software to read the data from Earthmate, and generate the $GPRMC sentence. He has kindly made it available as an OCX for others, via his web site. It just needed someone to embed this OCX into a suitable driver program (e.g. ROCKWELL.EXE) with the required code to drive the NMEA messages into GPSS.

In June 1999, Tooraj in Australia did the required work, which was made available for people to use for several years as an "eartha2nmea" software driver for free download. However, Tooraj no longer supports this free software. For the record, the old page, which no longer exists, was: www.ozemail.com.au/~tooraj/eartha2nmea.htm. see new link above.

Here is the link to Martin's site holding EM1.ZIP at 1.5MB near bottom of page :

The following information is now 'history', and put up for use by Tooraj.

Here is a brief description of the internal interface into GPSS:

The interface is crude, by works under most Windows environments including 3.1, 3.11, 95, 98, NT, OS2, with the 'Driver program' as a DOS or Windows task. The ROCKWELL.EXE program would use Martin's OCX to generate the NMEA $GPRMC strings from incoming binary data.

ROCKWELL.EXE starts first and writes (any data) into a flag file GPSS.LLF in same directory as GPSS.EXE. GPSS.EXE is started, sees GPSS.LLF present, so skips opening the COM port, and expects the NMEA data in a text file GPSS.LLD

After reading the line of NMEA data in GPSS.LLD, GPSS deletes GPSS.LLF to indicate the data has been read. It then responds to the $GPRMC message as if it had arrived from the COM port, then loops (giving time away to other tasks by calling DOEVENT) until it sees GPSS.LLF appear again.

The logic of ROCKWELL.EXE simply needs to read the COM port, write the $GPRMC line to a created file GPSS.LLD then create the flag file GPSS.LLF.

It then loops (calling DOEVENTS) until the GPSS.LLF is deleted. Alternatively, it could use a Timer instead of loop and DOEVENTS. All crude and simple stuff - just a few lines of code - but works OK.

Should be easy to test the above logic, by putting a copy of GPSS.LLD and GPSS.LLF in with GPSS.EXE, before running GPSS - it should respond as if it came from the COM port.