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1996-09-03
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GPS information shipped with Mapper-3a/GB v4.5
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If you're a die-hard Mapper-3a fan from the old days (i.e. before a month
or three ago!!!) you may be happily using Mapper-3a as it was originally
intended, as a standalone Geographical Information System. And very good at
this it is too.
What's rather caught my imagination in the last few months has been the
possibility of hooking the Psion up to a GPS (Global Positioning System)
unit, which are now available for a few hundred pounds (though don't buy
the cheaper models) and which are smaller than the Psion.
In case you're not sure what a GPS is, it's a small unit with a built-in
aerial which receives positioning information from the american GPS
satellite system (see picture) to tell you your current latitude,
longitude, velocity, altitude etc.
By hooking the two together the possibility exists to use the Psion 3a as
a very flashy real-time moving-map display. Let me give an example:
You're about to leave Basingstoke (wise move) and have set up Mapper-3a at
x32 zoom, high detail, sticky Roads and sticky Little Chefs. Normally,
this would be it. You'd look at the screen, note the restaurant half-way
to Reading and then turn off the Psion and set off. However.....
With a GPS sitting on the dash-board, and happily chucking out latitude,
longitude, bearing etc down the wire into your 3a, you can now 'select'
this particular Little Chef, leave the Psion ON (or turn it ON when you
actually need to, of course) and it will show you, in real-time, a black
cross showing your position (hopefully on the A33!), a bearing line to
show your current direction of travel, and estimated time of arrival at
the restaurant! Cool, eh, although in Mapper-3a/GB's case you have to
allow for the fact that things are only done to 1km accuracy.
Of course, if all this seems like whimsical gadgetry to you, you're
probably right, but then I like gadgets! My Garmin GPS45 cost about †255
including VAT in October 1995 from a London dealer.
Note that ETA etc are calculated using your set average speed in your
personal preferrences. I've tried using actual speed from the GPS etc, but
so far the results are just as transient and and/or approximate as using a
set average ... watch this space ...
So what do you need if you want to try all this out?
* Psion 3a with 150k of free system memory (100k needed by the program,
and 50k margin for other programs you might start and stop during the
running of Mapper-3a)
* Installation of Mapper-3a/GB v3.6 or higher
* 3-Link cable (or at least the part with the 'podule' on)
* GPS receiver with NMEA 0183 v1.5 or higher interface (one of the
Garmin units is ideal) and data cable to the 3-Link connector or
podule.
Also worth thinking about is integrating power leads for your 3a and GPS
into the wiring if you intend to run them both for long periods! Note that
the Psion doesn't *have* to be on all the time, you can just turn on when
you need a 'fix'!
Acquiring the above
-------------------
I'll assume you already have a Psion 3a and 3-Link, or you probably
wouldn't have got this far! First item on your shopping list is to buy a
GPS. The next bit's the tricky one.
The easy way to connect all this together is to contact Peter Kitsen at
Positioning Ltd on 01403 271114, as he has the expertise and stock to
offer advice on and to put together all the elements you might want, from
cables to cradles. Or try Maritec on 0141 5542492, who do cables from most
GPS systems to the Psion podule.
The more 'Do-It-Yourself' approach is to make up, or get made, a cable to
go from the GPS to the Psion podule yourself. As most GPSes have different
connectors, you'll need the specific data cable for your unit from the
manufacturers, which is normally about 20 pounds. You'll then need a
mini-DIN connector (get this from Maplin) soldering on the end with the
bare wires. Note that you can get car-phone cradles fairly cheaply, which
are effective at holding GPSes in position in a car.
Getting the GPS link working
----------------------------
Assuming you now have all the bits you need:
1. Plug everything in
2. Start up the GPS and position in your car to get good satellite
reception. I find it works very well wedged on top of the dashboard,
but if you have a heated windscreen this may be a problem for you, as
the mesh of wires can block the signal.
3. Start up Mapper-3a and go to the map you want the moving map icon
displayed on-top of, and set your required sticky displays/options. If
you're wanting to try out the ETA/Distance left option, choose your
settings in the 'Moving Map Settings' dialog, and 'select' a
destination (place or overlay item) by 'find'ing it in the usual way.
When all is ready, select 'GPS Moving Map' from the right-hand menu.
4. If all is well, you'll see one of two icons on your map. Either a
cross-hair showing current position or a 'Poor GPS' icon. The latter
will appear whenever your GPS's output quality deteriorates to warn
you that it doesn't really know where it is anymore. Try waiting or
re-positioning your GPS ....
5. If the cross-hairs get too close to the edge of the screen, the map
will re-centre itself and stay in 'GPS Moving map' mode.
Have fun!
Extra notes
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* If you haven't got a GPS yet, there is a little simulator routine
built into the program to show you what you'd see
* If you should blow anything up or injure yourself in any way, please
note that I take no responsibilty whatsoever for use of this software
product! And if you're driving, keep your eyes on the road! I mean it!
ONLY USE THIS PROGRAM ON THE MOVE WHEN SOMEONE ELSE IS DRIVING. IF YOU
*DO* USE THIS ALONE ON THE MOVE, I WILL NOT BE HELD RESPONSIBLE WHEN
YOU CRASH HEAD-ON INTO A JUGGERNAUT!!!
* Technical one, this. Your GPS map datum should be set to WGS 84, if
it's not already! Also, the NMEA version supported by Mapper-3a is
0183 version 1.5. Mapper-3a normally gets its information from the
NMEA sentence $GPRMC, so if your GPS doesn't output this word you're
last hope is to go into the moving map settings dialog and select
'Magellan (Position only)', which tells Mapper-3a to go for the
lowest common denominator and use $GPGLL instead, although this only
gives position and not velocity or heading. Worth a try though, if
you're having problems!
See also my guide on troubleshooting GPS operations, below.
Recommendations for purchasing a GPS
------------------------------------
Don't buy the cheapest models! They may not have the right NMEA computer
interface! Shop around before deciding which model to buy or how much to
pay! Start looking at the Garmin units (30,45,55,65,75,90 etc), which have
a very good reputation.
Places to try in your quest
---------------------------
* Positioning Ltd on 01403 271114
* Pumpkin Marine on 0171 4806630
* Garmin UK on 01794 519944
* Maritek on 0141 5542492
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Troubleshooting GPS operations
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So, you've been trying out Mapper-3a on your Psion with your new GPS
gadget. And it doesn't seem to work, either at all or terribly reliably ...
Well, you're in the minority, because there are lots of people out there
using it all quite happily together, but I accept that what with all the
things that could go wrong, a few brief notes might be in order!
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Things to think about and look out for:
* Are you using the latest version of Mapper-3a? If not, why not?
* Is your GPS 100% compatible with NMEA 0183 v1.5 and above? Mapper-3a
needs the $GPRMC word output every 2 seconds or more