Global Positioning System (GPS) receivers provide users with information about their geographic position. Although there is a plethora of choices when it comes to selecting GPS hardware, for a moderate-sized field course where several to a dozen or more units need to be purchased, consumer grade GPS receivers should prove more than adequate in positional accuracy in the typical outdoor settings of field camps. All modern GPS receivers will be capable of monitoring 12 satellites simultaneously, yielding ~10 m accuracy in location. If higher accuracy is desired, many new GPS receivers incorporate the Wide Area Augmentation System (WAAS), which is real-time differential correction system developed in part by the Federal Aviation Administration (FAA). The WAAS system offers real-time accuracy of 1-3 meters in horizontal position, but it is available only in North America at this time.
Choosing a GPS Form Factor
GPS receivers have become almost ubiquitous in the past few years, and can now be found in phones, cameras, computers, and watches. This explosion in the use of GPS has lowered hardware prices significantly, but has also led to a sometimes overwhelming number of choices when it comes to choosing GPS hardware. Generally, there are three categories of GPS hardware from which to choose. These are wireless, integrated, and handheld receivers. Each is discussed in some detail below, with a list of pros and cons of each variety.
Wireless GPS Receivers
Wireless GPS receivers transmit GPS position information from the GPS receiver to a handheld, tablet, or laptop PC without the use of wires. The most common wireless connection for GPS receivers is Bluetooth radio. Bluetooth connectivity is already integrated into most laptop computers, and is available as an integrated option on many tablet and handheld PCs (as well as cell phones), or can be added to an existing computer with an internal or external expansion card. Bluetooth radio works over fairly short distances; up to 30 meters under ideal conditions, with 10 meters a more reasonable expectation. There are a variety of advantages to using a Bluetooth wireless GPS receiver. The radio connection means that the GPS receiver can be optimally located, on a hat, in the top of a backpack, or on a dashboard, to get the best GPS reception. Since the receiver broadcasts the GPS position information, several students in a mapping group can share a single GPS receiver. The lack of cables and wires hanging off of a field computer make tripping over it or dropping it less likely, and leaves the computer more sealed to environmental contamination. Disadvantages are that Bluetooth GPS receivers are somewhat more expensive than other options, and few Bluetooth receivers have displays, so they are non-functional without an additional piece of computer hardware. Many also have internal rechargeable batteries, such that a power point is required to recharge them, often more than once through the course of a work day.
Integrated GPS Receivers
Integrated GPS receivers attach to a handheld, tablet, or laptop computer, rendering a single, integrated computer/GPS unit. Integrated receivers can be proprietary, and thus specific to a particular make and model of computer, or generic, and thus compatible with many types of computers. One advantage of almost all integrated GPS receivers is that they use the host computer's power source, so there is no need for additional batteries or charging capability.
Proprietary Integrated GPS Receivers
Proprietary integrated GPS receivers are designed to work with a specific brand or model of laptop, handheld, or tablet computer. In some cases, particularly with handheld PCs, the proprietary integrated GPS unit is installed inside the computer during fabrication. In other cases, such as many rugged Tablet PCs, the GPS unit is an external add-on or option. The advantages of a proprietary GPS unit are that setup and installation are likely to be straightforward with no hardware compatibility issues. The units designed to accompany rugged PCs preserve the environmental seal of the PCs and are often designed with break plates such that if you drop the unit, a cheap plastic plate snaps and saves both the GPS and the PC. Disadvantages of the proprietary units are the cost, which can be substantially more than other GPS options, and the fact that the GPS units are compatible, and therefore functional, with only a specific type of hardware.
Generic Integrated GPS Receivers
Generic integrated GPS receivers connect to a host computer using one of the common types of expansion slots. The most common of these are CompactFlash (CF) or SecureDigital (SD), both of which are standard on handheld computers, and which can be added to most laptop or tablet PCs through the use of an adapter card in the PCMCIA slot of the laptop or tablet. There are a few PCMCIA GPS receivers available on the market, as well as USB GPS receivers. The advantages of these add-on GPS receivers is that they can be used with virtually any type of computer hardware, and that they are relatively inexpensive. Disadvantages are that they can create an awkward appendage, particularly on laptop or tablet PCs, that is easily bumped, bent or broken, and that the GPS card itself is useless without a host computer.
Handheld GPS Receivers
Handheld GPS receivers have been around for years and are the most common type of GPS receiver to many people. Most handheld GPS receivers have a PC interface that allows them to connect to a computer and provide real-time GPS position information. Such a connection requires a cable from the handheld GPS receiver to the computer. The GPS receiver often has a proprietary connection, while the computer end is frequently a standard 9-pin serial connection. The advantages of handheld GPS receivers for use with GeoPads is that it may be possible to make use of an existing pool of GPS hardware with the purchase of a connection cable. The GPS receivers can be used with or without a computer attached, so they are functional for a wide variety of uses. Disadvantages are the cabled connection can be difficult to work around, and special cables and adapters are required to connect most GPS receivers to handheld computers. Handheld GPS receivers also require there own source of power, usually AA batteries.
Making a Choice
There is no one right GPS solution for use with a GeoPad. Existing hardware, price point, and ease of use must all be considered when selecting GPS hardware to complement a field computer.
Integrating with ArcGIS
ArcGIS does have built in tools for integrating with the handheld GPS. However, it only works with serial cable connections. Since most laptops, tablets, and GPS units no longer have serial connections, several companies have built software work arounds. Follow the link the Geopad Software
page and read about GPS Utilities.