Global Positioning System (GPS) Buying Guide

How does GPS work?

The Global Positioning system is made up of three major segments – Space, Control and User.

The Space segment consists of satellites that are continuously orbiting the earth at a consistent speed in a pre-fixed orbit zone. Each of these satellites circles the earth twice in 24 hours. To ensure that these satellites are detected from everywhere on the earth, they are divided into different groups and are positioned in such a manner that at any given time, any GPS receiver on earth can receive signal from at least four satellites.

The Control segment has a Master Control Station (MCS) and an Alternate Master Control Station, plus dedicated and shared ground antennas and monitor stations. It consistently monitors signal integrity, satellite health, and orbital configuration from the base.

The User segment comprises of all GPS receivers that receive and process navigation signals emitted by the GPS satellites. Due to these accurate signals, location can be fixed close to a few feet, time can be calculated close to a millionth of a second, and velocity can be measured close to a fraction of a mile/hour. All this information is relayed on the GPS receiver’ display screen.

The location of a GPS receiver on earth is marked through a process called 3D tri-lateration. As the satellites continue to orbit the earth, there are points when three satellites intersect each other to create intersection points, which in turns points out towards the GPS receiver’s location. The GPS receiver calculates the difference between the time the signal was transmitted and the time it was received. This number determines how far away the satellite is. Similar distance calculations from a few more satellites, helps the receiver determine the user’s position and depict it on the receiver’s electronic map.

Often atmospheric conditions like altitude change and humidity create glitches in location reading. Error can also occur due to multipath effects in congested areas where signals are bounced off mountains and buildings and firm ground. To counterbalance these aberrations, most GPS receivers come with an automated error correction feature.

GPS being a real-time application, the receiver’s built-in software is continuously recalculating this data as it moves from one place to another.

Application of GPS

Some of the areas in which GPS technology is used are listed below:

1. Tracking and Driving:

• Used for tracking vehicles – stolen or involved in an accident.
• In-vehicle GPS receivers plot the vehicle’s position on an electronic map to help driver determine his/her current location.
• GPS unit is preloaded with 2D and 3D maps and millions of Points of Interest (POIs), and usually features support for turn by turn voice instruction, best route calculation, re-routing, and traffic updates.
• Helps mark waypoints, add customized POIs, trip routes, trip logs etc.

1. Marine:

• Fish-finders help fishermen find populated fishing areas and track migration of fish. The Lowrance handheld GPS is a popular choice for marine applications. 
• Along with Sonar capabilities the Marine GPS unit can mark the exact fishing spots and navigation waypoints as deep as 1500 feet.

1. Sport and games:

• Help find locations marked in the clues of games like geo-caching and orienteering (specialized geocaching GPS).
• Assist avid Golfers with details about golf courses including hazards, layups and fairway targets.

1. Adventure navigation:

Assist explorers, mountaineers, wildlife researchers and others who work in uncharted regions to track their way back to mainland.

1. Multimedia Facilities:

• Multimedia capable GPS units provide entertainment on the go. Listen to music, watch videos or photographs via an external SD memory card.
• USB 2.0 connectivity allow the GPS unit to share and transfer data with a PC or laptop.

Some of the other major applications of the GPS technology include space navigation, safety and rescue operations, land surveying, farming, aviation, geological applications, time synchronization, environment and military applications.

A few points to bear in mind when purchasing a GPS

Let’s take a look at some important features that you should consider before buying a GPS unit.

1. Screen: GPS screens range from 3.5” to 4.3” for small to medium sized cars and 5.6” for larger vehicles. A large screen with a wide viewing angle helps you read menu commands, instructions, street names and map details clearly. This is particularly helpful for in-dash GPS units. However, too large a screen can be obstructive. But if your GPS unit is equipped with the text-to-speech feature then the need for glancing at the screen is greatly reduced. High-end GPS receivers now come with interactive touch screen color LCD displays. Some come with displays that can be adjusted to suit varying lighting conditions. For easy reading and clarity opt for an anti-glare screen.

1. Mounts: Most car GPS units can be mounted on the windscreen or the dashboard, from where you can easily view the screen. In-dash or in-car units are fixed, while portable units are transferable between different vehicles thanks to their easy-to-fix mounts. Some mounts fold flat in the rear allowing you to carry it easily in a purse or a pocket.

1. Text-to-speech vs. Voice prompts: Text-to-speech is one of the most sought after features in GPS devices. The navigation unit will clearly read out the street names unlike voice-prompts that will just instruct you to “turn left” or “turn right after 100 meters”. For e.g. the GPS unit will instruct you with “turn left on St. Peter’s street”. This helps you stay focused on the road ahead, instead of having to refer back to the display screen.

1. Number of channels: The new models of GPS receivers are capable of receiving signals from 12 to 16 and more channels. Channels represent the number of satellites the receiver is capable of monitoring simultaneously. For example, the Garmin eTrex GPS, one of the most popular Garmin model, is a 12 channel system. More the number of channels read, more accurate is the GPS reading.

1. WAAS / EGNOS: High-end GPS receivers support Wide Area Augmentation System (WAAS), which is a combination of orbiting satellites and ground stations that work together to enhance the receiver signal and take corrective action to increase the accuracy of location detection. GPS receivers work best in open areas, however, WAAS enabled units are capable of catching signals even under thick foliage, in deep canyons and in cloudy weather. EGNOS or European Geostationary Navigation Overlay Service is the European counterpart of WAAS.

1. Points of Interest (POIs): These are common but highly useful destinations that are preloaded onto your GPS device. POIs can include banks, ATMs, hospitals, gas stations, hotels, shopping malls and several other useful businesses. If you have run out of gas and want to reach a gas station, simply select that POI and the GPS will automatically guide you to that destination. Depending up on the model, most GPS devices feature over 3 million POIs. Some units also allow you to add your customized POIs.

1. Map detailing: Most GPS receivers are preloaded with some maps. However, a wider map database and a higher degree of map detail enhance your navigation power. GPS receivers armed with city maps and street level maps are a good choice. Select GPS devices that allow you to download map upgrades from their websites or by allowing you to read from a preloaded external source such as a micro SD card. If your GPS device has USB connectivity, then you can download the latest maps onto your PC which can then be transferred to the GPS device. Before you buy a device check whether the manufacturer allows map downloads and if it is free or chargeable.

1. Ruggedness / water resistance: You don’t want to be left stranded with an accidentally damaged GPS unit when you are far away from home. Buy a unit that is tough, all weather proof and water resistant. This is especially helpful for those carrying handheld GPS receivers out to sea or on outdoor adventures.

1. Size: Older GPS units tended to be bulkier while the new models are slimmer, lighter and portable. There are pocket-sized GPS units, units that can be worn as a watch or hooked to the waistband of trousers. Garmin handheld GPS and Magellan handheld GPS are among the prominent ones when it comes to handheld GPS.

1. Multipurpose GPS: Explorers prefer advanced GPS models with a built-in altimeter, barometric pressure thermometer and a 3-axis electronic compass. This multi-panel device gives them plenty of useful data such as elevation and direction details and updates on pressure and climatic changes. Some units are also empowered to function as a Personal Digital Assistant (PDA), a digital multimedia device, fitness and heart monitor as well as a phone. High end models also come with a built-in camera. There are plenty of Magellan GPS and Garmin GPS systems that feature multipurpose functionality.

Choosing from Different Types of GPS Devices

After analyzing your specific GPS requirements, check out various features of GPS devices between different brands and models available online.

Handheld or wrist-strapped GPS receivers: Lightweight and rugged, handheld GPS units are preloaded with maps and are great for geo-caching, golfing, camping, hiking and trekking. These are also used for walking, jogging, running and can monitor speed, distance, pace and calories burned.

Car GPS units: are ideal if you are a long distance traveler. Car navigation units can be hooked up to your car’s DVD player to provide you with a graphic representation of the terrain you are passing through.

Fish-finders and Marine GPS: Marine handheld GPS are useful for marine-based purposes and to ensure that you don’t drift off course.

Biker’s GPS: Similar to car GPS, these are fixed onto the bike’s console, stem or handle-bar. These are often rugged, vibration resistant and waterproof.

GPS for animals: Small GPS receivers are constructed into animal collars to track their movements.

Final word:

While GPS receivers are durable and glitch-free it is advisable to confirm its warranty duration and coverage and after sales service by the manufacturer. Use this guide to narrow down your choices.