Offroad GPS navigation, concepts and software


GPS systems have become a part of our life. There is GPS in your car, in your phone, and maybe even in your toilet seat. However, most systems in use depend on maps, and how good are the maps. You enter an address or a landmark, and then you follow the instructions to that point.

However, its a big planet, and a large part of this planet does not have roads, or has roads which are not yet mapped. So how do you navigate the big bad wild, and live to tell the tale?

This article will first address the concepts and then give you a run down on some common software on various platforms.


GPS stands for Global Positioning system
Click on the above link and it will tell you all you need to know about GPS, and even more.
To give a gist, a GPS is nothing but a timer.
A GPS satellite broadcasts the following information
1. The time
2. Precise orbital position of ephemeris
3. Rough orbits of satellites and health of system.

Using this the receiver computes the distance to each satellite, and then via "triangulation" to put it crudely, simply tells where you are.
Two locate your position on a plane, you need to have 3 satellite "lock".
however, we live in a 3D world, and its not just the position, but altitude also which is important, esp when you are flying. So 4 satellites give you fix with altitude.

That said, you have heard "the more the merrier". More satellites locking means better accuracy. For example, the 4 satellites visible to you may be bunched together, that means you get a fix, but your "error" increases. Technically, DOP or Dilution of Precision is used to measure error. Many software simply use this DOP value and give you a more meaningful value in terms of "meters".

So with 7-8 satellites in view, you may have an error of 3-4 meters. Can't go below that. If you see 4-5 satellites, your error can be as high as 20 meters, or even more. In the USA, many "WAAS" or ground stations augment the GPS system, resulting in much greater accuracy of even 1 meter. They are mostly used by Aircraft, however many mid range receivers incorporate WAAS chip also, so when WAAS is enabled, your accuracy increases.

That said you have GPS systems which are 12 channel (can lock upto 12 satellites), 24 channel, and even 36 channel. But do not be fooled, even if you have a receiver which can lock 100 satellites simultaneously, you won't get to see more than 7-10 in the sky. So 12/24/36 does not make a difference. What matters is the power of the equipment and sky visiblity. Often around buildings(highrises) or under thick forest cover, you will find your GPS losing signal. This means you have a low power GPS chip inside. Mostly phones and the cheaper units have this problem. Trekking handhelds usually have powerful receivers.

On many car navigation units there is a small MMCX or MCX port at the back, where you can connect an external antenna. I use one, and they are available for around 10$ from eBay or dealextreme.

All your GPS receiver will do is get the time, and then output something called a NMEA sentence, which is latitude/longitude/current time/Altitude and a host of other information.

But let us concern with Latitude/Longitude/altitude and time, because that's what matters.

Now there are various ways of representing lat/lon. For example there is the decimal notation this is 23.43543 78.5435353 with positive numbers indication East and North, and negative numbers meaning West and South. Longitude 0 is GMT, west of which will be negative. North of equator will be positive, and south will be negative for latitudes.

Similar to decimal notations there are other ways also, like Degrees/Minutes/seconds. But do not fret with that. Various sites are available on the net which do on the fly conversion. Now is this enough? If I tell you that you are at 23.4545645N 78.545353E at 2388m at 14:00:45 11/09/2011 is that enough. Can you navigate with that?

Well, unless you have a built in mapping function in your brain, that information is totally useless. So that brings us to the next topic. "MAPS"


When most people talk about GPS systems, they are actually talking about the maps. Every GPS system in the world, from the 700$ garmin, to the 10,000INR Mapmyindia to a 50$ dealextreme unit will tell you Lat/Lon/Alt/Time. What makes the difference is the map database. Maps are nothing but a way to give "reality" to the GPS coordinates.

For example. If I told you: 28.612864, 77.229306 is a nice place to visit. You would scratch your heads. But if I told you "India Gate" is a nice place, it would instantly make you understand.

This is what MAPS do. They tell you what is where. When GPS receiver calculates that you are at 28.612864, 77.229306, on the map you will be shown standing at India Gate.

Different sources like Garmin/Mapmyindia/Satguide have their own maps, and their own fans. There are community driven open formats like Openstreetmap, and the big daddy of all, the Google map. However, we will not concern ourselves much with that, we are moving into the domain of "No Map Land" or "where the streets have no name". Before that, a lowdown on the GPS hardware.

GPS Hardware:

All GPS receivers have a "GPS Chip" which does the above job, and supporting hardware which allows running operating systems, mapping programs etc., etc.,
GPS Hardware can be of 4 types:

1. Dedicated GPS systems:
These are the handhelds from Garmin, Lowrance etc., Some Car GPS systems also fall into these category. Most Car GPS systems appear to be in this category. They have a proprietary OS, and limited capability. All you can do on these is do GPS stuff. Many good quality units from Garmin/Lowrance/Magellen are waterproof, allow waypoint and track nagivation, as well as advanced stuff like perimeter scouting etc., They are built for the wild. However they their problems. You are limited by the software installed on your device. Multi tasking is not possible, and if the mfr does not have maps for your country, you will be staring at an empty white screen.
For most of these units, except Garmin, making India maps is a big task

2. PND - Personal Navigation Devices:
These are the ones you use in the car. Usually with 3.5-7" screens, they appear to run proprietary software, but actually they run Windows CE under the hood. If you search online, you can find many sources with information on how to unlock your device, i.e. expose the Windows CE Shell of your device, and then install any Windows CE application you want. Till the advent of mobile phone GPS, these used to be a rage, esp in the west, but now they are on a back foot thanks to the cell phone.

In India MMI/Satguide make these, and you can also source Garmin Nuvi etc., Most of these are difficult to unlock, and this makes many of these useless for offroad navigation, as softwares like Destinator(Satguide), Mireo(MMI) are useless for offroad navigation. Some Garmin PNDs have track and waypoint support with offroad mode, but they are expensive. If you are in the market for a GPS and do not care about routing and all, but mostly about making your own route, or using google JPEG maps and then calculating route yourself. I would suggest you buy one from ebay or dealextreme.

A 4.3" screen will set you back some 60$, and for 100$ you can get a 7". If you want somewhat better quality, get a Mio C320 or Mio C520 from some friends in US (Prices range from 90-200$ and keep fluctuating faster than onions). For you beginners, I suggest spend 50$ and get a cheap ebay unit with Windows CE. That way you can experiment, and later decide what you really want.

That said, many of these units can run Windows Mobile apps too, since underlying OS is very similar.

3. Mobile Phones:
The name itself is self explanatory. I have clubbed mobile phones under one category, but to be honest there are 5-8 smartphone OS out there. Every one has their own app support. iPhone and Android have the most number of apps, followed by Windows Mobile and Symbian. But do note that the screen will be small(unless you use a tablet) and if you get a lot of phone calls, you will be disturbed frequently and your navigation app will pause momentarily.

4. Dongles and loggers:
These are small things which can fit into a childs hand. All they have is an on-off switch, an internal battery, and a charging+USB port. The start logging from the time you switch them on. There are some units with bluetooth support. They are used for two purposes:

As loggers - Many of them have memory to support 1 million track points, and even on a curvy mountain road where track point frequency will be high you can get 10,000kms of logs. Some dump a trackpoint every second, and on such units you can have 1000-5000km log depending upon your speed.

As external GPS - What if you want to navigate on your laptop. You can install navigation software but how will you get GPS signal. These "loggers" also called bluetooth GPS dongles come to the rescue here. with bluetooth or NMEA cable interface, they will send trackpoint details to your PC, and the software there will give your position in real time.
For example. if you look at Google Earth menu, you will see an option for "connecting GPS".

Now we move on to the next topic, Offroad Navigation.

Offroad Navigation : Concepts
Offroad Navigation can be of three types:

1. Discovery type
In this you do not know where exactly you want to go. All you know is that if you keep on heading northwards, you will find a path in the mountains and then you can cross it. This obviously involves lot of hit and trial. Here your offroad navigator will keep on plotting your track. So if you get lost, you can retrace your path, or you can keep watching your track progress so that you do not keep hitting the same points again. That said, doing this is pretty rate. Tools like Google Earth give you excellent satellite coverage, so you can get a pretty fair idea of "Where I should be". So we will come to the second part

2. Waypoint Navigation
This involves a certain lat/Lon combination, or a set of lat/lon combination. So you have an offroad terrain where you are standing at. You know you want to be at XX.XXX/YY.YYY
Your navigator will tell you direction and distance as the crow flies. Its upto you then to form the easiest path.

3. Trackpoint Navigation
This is the easiest and the most dangerous. It means your friend has done a track, and given you the tracklog. You load that track in your offroad navigator, and just follow the path. You do not have to use your brain much. That brings the danger. I may have crossed a minor stream few months back, and now its a slush trap after the rains. Following my track can lead you in serious trouble.

I will not cover discovery navigation in detail, as covering Track and Waypoint navigation will teach you a lot of things about doing discovery navigation. In the next post we will look at Waypoint navigation in detail.

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