A number of GPS receivers are on the market. Usually a GPS receiver with more features costs more.

GPS manufacturers have done a pretty good job making user interfaces easy to use. After you know the basic concepts of GPS receivers and are familiar with a manufacturer’s user interface, a GPS Tracking Device is usually as easy to use as a cellphone and easier to use than a personal computer.

Display and output

GPS receivers have three choices for information display or data output:

   Monochrome LCD screen: Most GPS receivers have a monochrome liquid crystal display (LCD) screen.

Color screen: These are especially useful for displaying maps.

Color screens usually have shorter battery lives than monochrome ones.

   No screen: Some GPS receivers only transmit data through an expansion slot or a cable; a receiver with a cable is often called a mouse GPS receiver because it resembles a computer mouse.

   Such receivers are designed to interface with a laptop computer or PDA running special software. The picture below shows a DeLorme Earthmate GPS unit attached to a laptop. All

GPS data is sent to the laptop and processed there with mapping soft-ware. A Magellan SporTrak GPS receiver is shown on top of the laptop for comparison.

Most GPS receivers that have screens can output data to a PC or PDA.

A GPS receiver’s screen size depends on the receiver’s size. Smaller, lighter models have small screens; larger units sport bigger screens.Generally, a bigger screen is easier to read. Different models of GPS receiver also have different pixel resolutions; the higher the screen resolution, the more crisp the display will be. For night use, all screens can be backlit.

Alarms
A GPS receiver alarm can transmit a tone or display a message when you approach a location that you specify. This feature can be especially useful when you’re trying to find a place and visibility is limited by darkness or inclement weather — or you’re busy doing something else and aren’t looking at the GPS receiver screen.

Built-in maps
Every GPS receiver has an information page that shows waypoints and tracks. The page is a simple map that plots travel and locations. It doesn’t show roads, geographic features, or man-made structures.

Some GPS receivers have maps that show roads, rivers, cities, and other fea-tures on their screens. You can zoom in and out to show different levels of detail. The two types of map receivers areBasemap: These GPS tracker device have a basemap loaded into read-only memory that contains roads, highways, water bodies, cities, airports,railroads, and interstate exits.

Basemap GPS receivers aren’t expandable, and you can’t load more detailed maps to the unit to supplement the existing basemap.

Uploadable map: More detailed maps can be added to this type of unit (in either internal memory or an external memory card). You can install road maps, topographic maps, and nautical charts. Many of these maps also have built-in databases, so your GPS receiver can display restau-rants, gas stations, or attractions near a certain location.

Refer to the picture to see screens from a GPS receiver with a simple plot map and another GPS tracking device with an uploadable map.

GPS receivers that display maps use proprietary map data from the manufacturer. That means you can’t load another manufacturer’s or software company’s maps into a GPS receiver. However, clever hackers reverse-engineered Garmin’s map format. Programs on the Internet can create and upload your own maps to Garmin GPS receivers; GPS mapper is popular.A handheld GPS receiver’s screen is only several inches across. The limitations of such a small display certainly don’t make the devices replacements for traditional paper maps.

Electronic compass
All GPS receivers can tell you which direction you’re heading — that is, as long as you’re moving. The minute you stop, the receiver stops acting as a compass. To address this limitation, some GPS receivers incorporate an electronic compass that doesn’t rely on the GPS satellites.

Operation
Like with an old-fashioned compass, you can stand still and see which direction your GPS receiver is pointing toward. The only difference is that you see a digital display onscreen instead of a floating needle.

On some GPS receivers, you need to hold the unit flat and level for the compass to work correctly. Other models have a three-axis compass that allows the receiver to be tilted.

Paying attention to these factors can improve the performance and convenience of an electronic compass:

   Magnetic fields: Metal objects, cars, and other electronic devices reduce the accuracy of any electronic or magnetic compass.

   Battery life: Using an electronic compass can impact battery life. Some GPS receivers have settings that turn off the compass or only use it when the receiver can’t determine a direction from satellite data.

Calibration: Electronic compasses need to be calibrated whenever you change batteries. If your GPS unit has an electronic compass, follow your user guide’s instructions to calibrate it. Usually, this requires being outside, holding the GPS unit flat and level, and slowly turning in a circle twice.

Altimeter: The elevation or altitude calculated by a GPS receiver from satellite data isn’t very accurate. Because of this, some GPS units have altimeters, which provide the elevation, ascent/descent rates, change in elevation over distance or time, and the change of barometric pressure over time. Calibrated and used correctly, barometric altimeters can be accurate within 10 feet of the actual elevation. Knowing your altitude is useful if you have something to reference it to, such as a topographic map. Altimeters are useful for hiking or in the mountains.

Increasing accuracy
Some GPS receivers have features that allow you to increase the accuracy of your location by using radio signals not associated with the GPS satellites. If you see that a GPS receiver supports WAAS or Differential GPS, it has the potential to provide you with more accurate location data.

WAAS
WAAS is a Federal Aviation Administration (FAA) system, so GPS can be used for airplane flight approaches. The system has a series of ground-reference stations throughout the United States. These monitor GPS satellite data and then send the data to two master stations — one on the west coast and the other on the east coast. These master stations create a GPS message that corrects for position inaccuracies caused by satellite orbital drift and atmospheric conditions. The corrected messages are sent to non-NAVSTAR satellites in stationary orbit over the equator. The satellites then broadcast the data to GPS receivers that are WAAS-enabled.GPS tracker device that supports WAAS has a built-in receiver to process the WAAS signals. You don’t need more hardware. Some GPS receivers support turning WAAS on and off. If WAAS is on, battery life is shorter (although not as significantly as it is when using the backlight). In fact, on these models, you can’t use WAAS if the receiver’s battery-saver mode is activated. Whether you turn WAAS on or off depends on your needs. Unless you need a higher level of accuracy, you can leave WAAS turned off if your GPS receiver supports tog-gling it on and off. WAAS is ideally suited for aviation as well as for open land and marine use. The system may not, however, provide any benefits in areas where trees or mountains obstruct the view of the horizon.

 

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Sometimes this is displayed when the GPS receiver is turned on, or it might be shown on an information page. Consult your user’s guide or the manufacturer’s Web site for specific instructions on how to get this information for your model.

 

 

If you have a JIMI GPS receiver, you can sign up for automatic e-mail notification of firmware upgrades at the JIMI Web site. I expect other GPS Device Manufacturer to start offering this service.

 

3. Find your GPS receiver model and check its manufacturer’s website for the latest firmware version.

 

If your firmware is older than the current version on the website, follow the online instructions to download the firmware installer. Usually, the higher the version number, the more recent the firmware version. Make sure that the firmware installer you download is for your GPS receiver model. If you upload firmware designed for a different model, plan on the GPS receiver not working until you load the proper firmware.

 

 

A standalone program that runs on your computer, connects to the GPS receiver, and sends the upgraded firmware to the receiver. You need to have a PC interface cable attached to both the computer and the GPS receiver.

 

A special file that you copy to a memory card. When the GPS receiver starts, it searches the card to see whether a firmware upgrade is present. If it is, the receiver uploads the upgrade. After the upgrade is successful, you can erase the firmware upgrade file from the memory card.

 

Upgrading a GPS receiver’s firmware is pretty easy; not too much can go wrong. About the only thing that can get you in trouble is if the GPS receiver’s batteries die midway through a firmware upload. A firmware upgrade usually only takes a few minutes to complete, but make sure that your batteries aren’t running on empty before you start. Some firmware update software works only on COM ports 1 through 4. If you’re using a USB adapter, (which is usually set to COM port 5 or higher) and are having problems connecting to the GPS receiver, try reassigning the existing COM ports to numbers higher than the USB adapter’s port; then set the adapter’s port number to 1. Refer to online Windows help (choose Start➪Help) and perform a search for device manager to get more information on changing device settings.

 

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If a static GPS control survey is carefully planned, it usually progresses smoothly. The technology has virtually conquered two stumbling blocks that have defeated the plans of conventional surveyors for generations. Inclement weather does not disrupt GPS observations, and a lack of intervisibility between stations is of no concern whatsoever, at least in postprocessed GPS. Still, electronic tracking devices is far from so independent of conditions in the sky and on the ground that the process of designing a survey can now be reduced to points-per-day formulas, as some would like. Even with falling costs, the initial investment in GPS remains large by most surveyors’ standards. However, there is seldom anything more expensive in a GPS project than a surprise.

 

 

These upgrades in accuracy standards not only accommodate control by static GPS; they also have cast survey design into a new light for many surveyors. Nevertheless, it is not correct to say that every job suddenly requires the highest achievable accuracy, nor is it correct to say that every asset tracking device survey now demands an elaborate design. In some situations, a crew of two, or even one surveyor on-site may carry a GPS survey from start to finish with no more planning than minute-to-minute decisions can provide even though the basis and the content of those decisions may be quite different from those made in a conventional survey. In areas that are not heavily treed and generally free of overhead obstructions, the now-lower C group of accuracy may be possible without a prior design of any significance. But while it is certainly unlikely that a survey of photocontrol or work on a cleared construction site would present overhead obstructions problems comparable with a static GPS control survey in the Rocky Mountains, even such open work may demand preliminary attention. For example, just the location of appropriate vertical and horizontal control stations or obtaining permits for access across privately owned property or government installations can be critical to the success of the work.

 

 

An initial visit to the site of the survey is not always possible. Today, online mapping browsers are making virtual site evaluation possible as well. Topography as it affects the line of sight between stations is of no concern on a static GPS project, but its influence on transportation from station to station is a primary consideration. Perhaps some areas are only accessible by helicopter or other special vehicle. Initial inquiries can be made. Roads may be excellent in one area of the project and poor in another. The general density of vegetation, buildings, or fences may open general questions of overhead obstruction or multipath. The pattern of land ownership relative to the location of project points may raise or lower the level of concern about obtaining permission to cross property.

 

 

Maps, both digital and hard-copy, are particularly valuable resources for preparing a static GPS survey design. Local government and private sources can sometimes provide appropriate mapping, or it maybe available online. Other mapping that may be helpful is available from various government agencies: for example, the U.S. Forest Service in the Department of Agriculture; the Department of Interior’s Bureau of Land Management, Bureau of Reclamation, and National Park Service; the U.S. Fish and Wildlife Service in the Department of Commerce; and the Federal Highway Administration in the Department of Transportation are just a few of them. Even county and city maps should be considered since they can sometimes provide the most timely information available. Depending on the scope of the survey, various scales and types of maps can be useful. For example, a GPS survey plan may begin with the plotting of all potential control and project points on a map of the area. However, one vital element of the design is not available from any of these maps: the National Spatial Reference System (NSRS) stations.

 

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Direct communication between vehicles allows information exchange without requiring any fixed infrastructure or base stations. The location and velocity of vehicles is constantly changing, and the RF communication range is of fairly short distance; therefore, the set of vehicles that can directly communicate will constantly change over a short period of time. This dictates that the physical layer and the network must be capable of operating in an ad hoc, decentralized manner, although coordination and synchronization through GPS ( GPS tracking device for cars ) time signals are possible. Any two nodes must be able to communicate securely whenever they are within communication range.

 

In a V2V network we can distinguish two modes of communication, usually designated as:

 

• Single hop: Two vehicles are close enough to communicate directly with each

other (either broadcast or point to point) with low latency.

 

• Multihop: Vehicles that can not directly communicate may forward messages through intermediate nodes.

 

Multihop communication has been the subject of much research, but no standard has emerged, and in fact the technical difficulties of establishing routing and acknowledgment protocols along with potentially high latency may limit its use to very specific applications such as medium range emergency notification or other sparse broadcast communication applications.

 

Many early experiments in V2V communication were carried out with standard wireless LAN technologies, and some success was achieved at ranges of up to several hundred meters. But the technical difficulties inherent in vehicle and traffic situations, including the high relative velocities (Doppler effects), a safety critical low latency requirement, operation in an urban environment (multipath), and spectrum competition from other users in unlicensed frequency bands renders this an unrealistic solution for commercial deployment. The IEEE 802.11p/WAVE standards have recently emerged as the current consensus for the implementation of V2V and local V2I communications.

 

Positioning of the vehicle is provided by a Differential GPS (DGPS)—Inertial Navigation System ( vehicle GPS tracking systems ). This vehicle position updates the vehicle positioning computer to make corrections to bring the vehicle back to its pre-programmed track. While the vehicle generally operates in an automated mode (autoheading and preprogrammed track), its operation can be immediately over-ridden by moving the rudder joystick or the throttle at the surface console.

 

There are existing standards for digital communication using subcarriers of standard AM and FM radio broadcast stations. Applications include channel and programming information, commercial paging systems, weather, news, and traffic information, stock market quotes, and GPS differential correction services. The data rate is quite low (on the order of 1 Kbps) and the services often require paid subscriptions. Many of these applications are declining in popularity due to the availability of other, faster technologies. Satellite radio offers a similar unidirectional capability at much higher data rates, for example, Sirius Traffic, a subscription service for real-time traffic data.

 

As we have previously mentioned, cellular telephone and broadband data services have become ubiquitous. Pricing, at least for individual users, is still rather high, but vehicle OEM and other providers have negotiated pricing arrangements for particular services. Perhaps the best known is the GM On Star service, which provides driver information including directions, stolen vehicle location, crash detection and emergency services notification, and other services. BMW Assist is a similar service. To date, these services have been implemented by specific vehicle manufacturers and are not available outside their vehicle brands.

 

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The following are some of the main errors that can potentially affect data acquired from GPS sensors (points 1 to 5), and that can be classified as GPS location bias, i.e. due to a malfunctioning of the GPS sensor that generates locations with low accuracy (points 6 to 9):

 

1. Missing records. This means that no information (not even the acquisition time) has been received from the sensor, although it was planned by the acquisition schedule.

 

2. Records with missing coordinates. In this case, there is a GPS tracking device failure probably due to bad GPS coverage or canopy closure. In this case, the information on acquisition time is still valid, even if no coordinates are provided. This corresponds to ‘fix rate’ error.

 

3. Multiple records with the same acquisition time. This has no physical meaning and is a clear error. The main problem here is to decide which record (if any) is correct.

 

4. Records that contain different values when acquired using different data transfer procedures (e.g. direct download from the sensor through a cable vs. data transmission through the GSM network).

 

5. Records erroneously attributed to an animal because of inexact deployment information. This case is frequent and is usually due to an imprecise definition of the deployment time range of the sensor on the animal. A typical result is locations in the scientist’s office followed by a trajectory along the road to the point of capture.

 

6. Records located outside the study area. In this case, coordinates are incorrect (probably due to malfunctioning of the GPS sensor) and outliers appear very far from the other (valid) locations. This is a special case of impossible movements where the erroneous location is detected even with a simple visual exploration. This can be considered an extreme case of location bias, in terms of accuracy.

 

7. Records located in impossible places. This might include (depending on species) sea, lakes or otherwise inaccessible places. Again, the error can be attributed to GPS sensor bias.

 

8. Records that imply impossible movements (e.g. very long displacements, requiring movement at a speed impossible for the species). In this case, some assumptions on the movement model must be made (e.g. maximum speed).

 

9. Records that imply improbable movements. In this case, although the movement is physically possible according to the threshold defined, the likelihood of the movement is so low that it raises serious doubts about its reliability. Once the location is tagged as suspicious, analysts can decide whether it should be considered in specific analyses.

 

GPS sensors usually record other ancillary information that can vary according to vendors and models. Detection of errors in the acquisition of these attributes is not treated here. Examples are the number of satellites used to estimate the position, the dilution of precision (DOP), the temperatures as measured by the sensor associated with the tracking platform and the altitude estimated by the GPS. Temperature is measured close to the body of the animal, while altitude is not measured on the geoid but as the distance from the center of the earth: thus in both cases the measure is affected by large errors.

 

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