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Accessories/GPS and Electronic Mapping:

Here is the GPS info I promised the group, this info was also found on the net. First of all, in order to use a GPS with mapping software, your GPS must have a PC/Interface cable and be able to connect to a serial port behind your Laptop/Notebook and also be NMEA compliant (which is usually a standard for the industry).

What Does "GPS" Stand For?

GPS stands for Global Positioning System. The Global Positioning System consists of a "constellation" (i.e., an organized group or system) of orbiting satellites which, in conjunction with ground equipment, enables users to determine their exact position anywhere on the surface of the earth at any time. There are currently two dozen satellites in orbit. At any time, with an unobstructed view of the horizon, there should be at least four to six satellites "visible". There is no charge for use of the satellite system, although each user must supply their own equipment, generally in the form of a handheld receiver.

How Does the System Work?

Basically, GPS uses relatively straightforward principles of geometry and trigonometry. Each satellite continuously transmits orbital data for the entire constellation of satellites in addition to timing data and other information. Thus, each GPS receiver has continuous access to precise orbital data from which the locations of all satellites can be calculated by the microprocessors contained in all GPS receivers. Since all radio waves, including those transmitted by the GPS satellites, travel at a constant speed (i.e., the speed of light), the GPS receiver can calculate the relative distances from it to the several satellites that it can hear by comparing the timing data transmitted by the satellites. Since the GPS receiver "knows" where each satellite is, it can calculate where it must be to be experiencing the relative propagation delays for the satellites that it is hearing.

On What Frequencies Does GPS Operate?

GPS operates at approximately 1.5 GigaHertz (GHz), which is 1,500 Megahertz (MHz). Transmissions are spread spectrum; thus, satellites do not interfere with each other. Will GPS Give Me The Elevation or Altitude? Yes. When it can hear a minimum of three satellites, a GPS receiver will give its surface (e.g., latitude/longitude) position. When it can hear a minimum of four satellites, GPS will also provide elevation/altitude. The altitude that pilots utilize, mean sea level (MSL), is actually a measure of the air pressure. The distance above sea level is calculated using a very complex mathematical formula and geophysical model. Depending on air temperature and many other factors, there can be a very considerable discrepancy between even a "correct" aircraft altimeter reading and the distance that one could physically measure. The elevation displayed by GPS is the system's attempt to calculate a "measured" (rather than a "relative") distance. For this reason (and the considerations noted under "Accuracy" below), people will experience some frustration trying to compare GPS-based elevation/altitude readings with those derived from aviation-based sources.

How Accurate is GPS?

The theoretical inherent accuracy of GPS is within about ten meters (a little less than 30 feet). However, for perceived national security reasons, the United States Department of Defense, which owns the GPS Satellite System, usually limits the accuracy obtainable by civilian (i.e., non-military) users. The actual specification is that the performance will be within 100 meters (about 300 feet). The real world reality is that the latitude/longitude position information displayed by GPS receivers will generally be within 120 to 180 feet.

S/A Dithering.
The accuracy is limited by a process formally known as Selective Availability (S/A) and commonly called "dithering". This is accomplished by manipulating the time data transmitted by the satellites slightly so that the resulting calculated position moves around slightly. This is a pseudo-random process so simple averaging will not remove all of the induced error. Military units contain a computer algorithm (i.e., program) that counteracts or corrects for the dithering. This is known as the P-Code.

The accuracy of the elevation/altitude information provided by GPS is significantly less than its surface location (e.g., latitude/longitude) information. Even a properly functioning GPS receiver may sometimes display elevation/altitude information with errors of 500 to 700 feet. In large part, this is because of the geometry to the satellites. Since the satellites are almost always more or less overhead, the angles are very steep. Another way of saying this is to compare it with the process of estimating the location of an object by triangulation. If one moves only a small distance (relative to their distance from the target) between each bearing, the lines cross obliquely and the resulting estimate of the target's location is imprecise. If the bearings are taken much farther apart, however, the lines cross at angles much closer to 90 degrees and the estimate of the target's location becomes much more precise and accurate.

At speeds under approximately two miles per hour, the effect of the dithering has a significant effect on the speed measurements provided by GPS. At faster speeds, however, the effect of the dithering is negligible since the dithering is generally gradual rather than abrupt. In my opinion, road speed measurements are extremely accurate when the vehicle is traveling in a straight line.

I Want The "P-Code"; Where Can I Get It?

P-code refers to the algorithm (computer program) contained within the firmware (i.e., computer chips) of military-version GPS receivers. The P-code is essentially a program which allows the receiver to decode and utilize an additional data stream transmitted by the satellites, the effect of which is to cancel out the error introduced by the dithering process. P-code is classified and available only to military users.

What is "DGPS" and Which Receivers Can Use It?

The acronym DGPS refers to Differential GPS. The DGPS process utilizes an additional receiver which receives and decodes a data stream from a land-based beacon station. At the beacon station, a GPS receiver calculates its apparent position by listening to the available satellite data. This position is then compared with the precisely known actual location of the beacon station. A correction factor is derived from this comparison and transmitted over the beacon. When operating in the differential mode, other GPS receivers apply the same correction factor to the position they are calculating from the satellite data. The result, which is displayed for the user, is free from much of the error that was introduced by the dithering process. The accuracy of the displayed DGPS location depends upon a number of factors including the quality of the DGPS data and the proximity of the remote GPS unit to the beacon to which its diversity receiver is listening. There are two basic types of DGPS beacon stations. Along the coastal areas of the continental United States, the United States Department of Transportation, Coast Guard, is installing numerous high frequency (i.e., HF or shortwave) beacon stations. The data transmitted by these stations is available without charge to the public. The purchase of an optional HF diversity receiver ("DBR") {JUMP TO MAGELLAN DBRs} is necessary to utilize this service. Additionally, there are several commercial services available which operate DPGS beacons. One of the largest of these, DCI (Differential Corrections Incorporated), has dozens of beacon stations across the United States. The data from these stations is transmitted on a subcarrier ("SCA") by commercial FM radio stations in selected markets. This service is marketed with three levels of accuracy available at increasing cost for higher accuracy options. The SCA beacon receiver must also be purchased by the user. The availability of this service depends upon the service of the FM station and it by no means covers the entire United States.

What Is the Difference Between an RST232 Dataport and a NMEA Dataport?

Not much. The serial datastream is exactly the same. It consists of a continuous stream of serial ACSII data representing GPS information such as position, elevation, heading, speed, and other information. The only difference is the voltage level of the electronic signals. NMEA is a TTL (i.e., "transitor-to-transitor logic" level which is approximately five volts); whereas, RST232 is a 12-volt level. In most applications utilizing a handheld GPS receiver and a notebook/laptop computer, there is no common ground reference between the two units. Thus, the ground is said to "float". This means that the notebook/laptop will see a five-volt shift in the NMEA datastream much as it would see in a somewhat weak RST232 signal. While I do not guarantee it, it has been our experience that most, indeed virtually all , notebooks/laptops will accept the NMEA level through their RST232 port. Moreover, it is extremely easy to construct (or fairly inexpensive to purchase) a circuit that will convert serial data at the NMEA level to true RST232 levels. "NMEA" stands for National Marine Electronic Association. It is the data interchange standard utilized by marine accessories, such as autopilots, depth sounders, and other marine navigation related equipment.

Which Type of Dataports Do the Units Have?

Generally speaking, marine-oriented units have NMEA dataports, land-based units have RS232 dataports, and aircraft units traditionally have a dataport that is user selectable for either RS232, R1/R0- K1/K0-X0/X1, or NMEA. The Trimble ScoutMaster and ScoutMaster Field Kit are RS232. The Magellan GPS3000, Meridian, Meridian XL, and NAV DLX-10 are NMEA, and the Skyblazer allow the user to select either NMEA or RS232 at any time through the keyboard.

Should I Buy an External Antenna for My GPS Receiver?

Maybe, but, frankly, you may want to see how well the unit operates with just its own antenna in your applications first. A couple of years ago (ancient history in the GPS world), external antennas were a very costly accessory. This was probably because external GPS antennas are proprietary (in that if you have a Magellan GPS you need a Magellan antenna, if you have Trimble GPS you need a Trimble antenna and so on). Today, external antennas, particularly for Magellan products, tend to be quite affordable. It has been our experience that many users will obtain adequate performance using the detachable antenna and short extension cords associated with many current models. An external antenna will, however, greatly enhance the performance of any GPS in a vehicle or aircraft. For users of the Magellan receivers with detachable antennas (Meridian, Meridian XL, Trailblazer, Trailblazer XL, and Skyblazer) we recommend the antenna clip suction cup mount and the low-loss antenna.

"Moving Maps."

The term "moving map" (or mapping program) on the other hand is generally used to refer to software, often including a CD-ROM disk, that contains computer readable and displayable maps of the relevant area. Most of the better moving map programs, such asthe VISTA family, also include plotting features. In the case of VISTA, most of the plotting capability lies within the "overlay" function. Moving map programs take input from a GPS locator, typically through the computer's serial port, in order to ascertain where the user islocated. This location is then displayed on the screen, typically with a mark or cursor that is customizable to the user's needs and which may, optionally, include either a "bread crumb" trail of the user's previous locations and/or a projection of the user's future locations based upon current position and direction and speed of travel. High end moving map programs also include various methods of easily creating waypoints and routes as well as providing course deviation indicators (CDIs or steer left/steer right indicators) to facilitate navigation. Many moving map programs offer various search methods including search by city name and search by street name.

I have found a really great computer map program but I am told that I need a "GPS enabler" or "GPS link". What are those things and do I really need them?

Unfortunately, many sellers of moving map programs charge significant amounts of money for their product. In order to make their product appear price competitive, they price the program, the maps, and the GPS modules separately. If you want a "moving map" rather than a manual or static map, you will need the software which will accept input from your GPS unit. These modules are sometimes called "GPS enablers" or "GPS modules". They are not physical devices, but merely software. Typically, they operate by taking serial ASCII data (typically at 4800 baud) in through the computer's comport. This data, typically in NMEA 183 B or C format, includes information concerning current position, heading, speed, time (and sometimes other information). The VISTA family of programs includes the GPS enabler in the basic price. A word of warning about a similar technique. Many moving map programs include only the program and a limited number of maps. If you want maps of all the cities or of the entire United States or of Alaska and Hawaii, etc., you have to buy additional maps. Although these often seem reasonably priced, anywhere from $39.95 to $19.95 each, the cost of acquiring say eight or ten cities can be staggering. In the case of VISTA USA, the CD-ROM disk supplied includes the entire United States with all of the streets, highways, roads, streams, railroads and whatnot for the entire United States together with Alaska and Hawaii. Shop carefully. There are 3 reasonable companies that make GPS mapping software at a reasonable price and depending on what you need. I will describe general features....

Its like a Thomas Bros. It's a reasonable guide for the street driver and what I'm currently using until I get VISTA. Its pretty straightforward..

Streets Plus-Deluxe Edition
Designed for both business and personal use, provides more than 6 million miles of NEW city maps, for all 50 states. It allows you to pinpoint virtually any address in the United States, including streets, small towns, and landmarks, and anything else that is on the map. You can easily put addresses on the map, add your own data to the map, and even add information from the American Yellow Pages+ CD-ROM, which is included in the Deluxe Edition. Streets Plus lets you further customize your maps with information from its database of nearly 300,000 hotels and restaurants, and from Automap Online with up-to-date information and further links for 425 cities and places. Streets Plus offers one-click integration with Automap Trip Planner and is GPS ready. The Deluxe Edition is a great value, a savings of more than $20 compared to purchasing Streets Plus and the American Yellow Pages separately.

VISTA (1-800-346-0045) -VISTA The Unlimited Moving Map and VISTA FULL VERSION
Is a low-cost moving map program which includes roads, streets, highways, freeways, rail lines, and perennial water courses throughout the entire USA, including Alaska and Hawaii. VISTA-USA, in conjunction with the user's computer (ideally a notebook) and GPS, will spot the user's position on road maps. The user will always have all of the necessary maps available for every city, town, and community in the United States since VISTA-USA includes vector maps of every location in the United States. In metropolitan areas, the names of virtually all named streets appear and in rural areas a surprisingly detailed array of roads (including dirt roads) appear, many with names or number designations. All major interstate, federal, and state highways appear with appropriate designations. It is important to note that, unlike virtually every other program in its price class,VISTA-USA ships with the complete map set. There are no gaps in coverage and there are no additional maps to buy. VISTA-USA includes all the software needed to navigate the cities and countryside of the United States. With the user's GPS receiver connected to the computer, VISTA-USA shows current position on detailed street maps. The user can zoom in to see detailed street information or zoom back out to see the big picture of a wide area. While the exact "zoom range" is determined by the amount of RAM available in the computer, a typical (8-megabyte) installation will allow zooming from approximately one-quarter mile across the screen to over 700 miles across the screen. Depending upon the user's preferences, VISTA-USA will "call up" the next map as the user moves from one location to another. The user may search for a specified city or town by entering a few letters of its name plus the two letter state abbreviation. The program will then call up and display that city. The user can then zoom in to whatever level of detail is desired. Additionally, the user can, while displaying a city map, enter the name of a street and the program will highlight (in the user's choice of color) that street.

Drag-n-Drop Waypoint Creator
The topographical database which is supplied with the program gives elevation for any point within the United States to the nearest 100 feet. The user's present location can be displayed in several ways including with or without a projected route and with or without a "bread crumb" trail showing the past route. Additionally, a data file can be created containing periodic "fixes" of the user's location. The course that has been"recorded" in this manner can then be "played" and will appear superimposed upon the appropriate map. The user can add additional detail to the maps in either of at least two ways. The user can create "permanent" waypoints which will appear along with the name entered by the user whenever a map including that location is displayed. Another way is to create an overlay file, which can then be used when needed. Naturally, distance (i.e. "range") and bearing from the user's current location to any other point on the map can be easily displayed. Similarly, bearing and range between any two waypoints is easily displayed.

With VISTA, the user can maintain continuous and accurate position information while zooming in to see greater detail or zooming out to see the big picture. The user can click on points of interest to discover precise location and navigation information. The user can switch between aviation, marine, and road maps. The user can make instant measurements between on-screen locations including graphic terrain crosssections. Navigation is facilitated by using VISTA's precise CDI (course deviation indicator). Its authors boast that "one minute the user has an ordinary paper map, the next minute, the map springs to life in a high-tech navigation instrument which can be used for worldwide travel." High claims, but accurate. In fact, VISTA is so unique and powerful that the United States Air Force adapted it for use by the Air Mobility Command after a year-long test program to verify accuracy, functionality, and ease-of-use. VISTA is compatible with thousands of aviation, marine, and land maps plus any scanned image. The following detailed full color maps are currently available on CD-ROM.

Aeronautical Sectional Charts for the 48 states.
Pilots worldwide use sectional charts to safely navigate general and commercial aircraft.

World Aeronautical Charts (WACs) for the 48 states.
The VISTA WAC CD-ROM also contains JNCs (jet navigation charts) of Western Europe, Canada, and Alaska.

-U.S. Road Map as described above under VISTA-USA (above).
This CD contains the entire United States including Alaska and Hawaii with street-level detail.

NOAA Marine Charts.
These high quality, accurate scans of the latest NOAA charts are scheduled for imminent release.

DMA (defense mapping agency) maps are available for military use.
This is a special military version of VISTA which is specifically designed for enhanced compatibility with the PLGR GPS unit manufactured by Rockwell. VISTA PLGR includes the capability to make selected combat calculations.


VISTA HQVISTA HQ is an enhanced version of VISTA designed to track multiple vehicles. In a typical application, each vehicle to be tracked will be supplied with a GPS receiver and a radio transmitter. The vehicle's position information is then transmitted by radio to an operations center. At the operations center, VISTA HQ, in conjunction with appropriate radio receiving equipment, receives and displays the location of the vehicles anywhere in the world and tracks their movements in real time. (Obviously, a full vehicle tracking package includes GPS receivers and radio equipment for each vehicle as well as radio equipment for the operations center; these items are not part of the VISTA HQ software package.) The basic VISTA HQ software package is capable of tracking up to 25 vehicles. Other versions are available for up to 1,000 vehicles. When utilizing VISTA HQ, the user is free to designate each vehicle with an appropriate name tag. To minimize screen clutter, name tags should be as short as possible. Since VISTA HQ includes all of the features of VISTA, the user can scan and use any maps appropriate for the intended application. Thus, VISTA HQ is an extremely flexible and full featured application. Note: Ham radio operators will note that packet/APRS would be ideal to provide the RF links necessary between each vehicle and the operations center. Thus, for search & rescue operations supported by amateur radio or public service events (such as marathons and parades) supported by amateur radio, VISTA HQ would make a striking, state-of-the-art mechanism to track participants and resources.

DELORME GPS MapKit + CD-$495
The GPS MapKit CD provides a low-cost solution for you to link a GPS satellite system to maps. Using a standard PC notebook computer linked to a CD-ROM drive and a GPS receiver, you can display your location on DeLorme's incredibly detailed maps anywhere in the country. The software interprets the data stream from a GPS satellite receiver to place a blinking dot on a moving map display. You can track your progress in a plane, a boat, a car or on foot. The map database is contained on a single CD-ROM. GPS MapKit software features: Constant visual indication of location, Active readout of latitude and longitude, Ability to monitor vehicle speed, direction and altitude, Incredibly detailed DeLorme maps, "Bread Crumb" function to trace your route, Ability to calculate approximate point-to-point and cumulative mileage, Ability to customize maps with routing details or other information, Integration with DeLorme mapping software, and much more!

AAA Map'n'Go 2.0 $39
1 million miles of routable roads, for the most accurate directions of any travel planner. Complete AAA listings and ratings for over: 22,000 hotels, 10,000 restaurants, 10,000 campgrounds, 15,000 attractions and points of interest, Listings for 1,000 AAA and CAA offices in the US and Canada, Detailed, street-level maps for 241 cities, Link to the Global Positioning System through an interface with DeLorme-approved GPS receivers, Link to Internet ( for up-to-date weather conditions and construction sites, and information about thousands of events in North America. Improved routing capabilities, including new scenic trip routing, Ability to customize maps with text and symbols, Link to Phone Search+ USA, DeLorme's CD-ROM phone directory for the US, Four printing options: Driving directions Overview map, Reports of points of interest that you select for your trip, Detailed strip maps, Ability to designate all hotels, restaurants, campgrounds and attractions, as well as places, as starting points, stopovers or destinations on your route, Narrated slide show for selected points of interest, Ability to E-mail travel plans to other AAA Map'n'Go users, Easy-to-use toolbar, intuitive design, Latitude and longitude display, Numbered highway exit ramp markers, Search by place, ZIP code or area code/exchange, Show or hide map detail , Set speed and travel preferences, Free 30" x 42" highway map of America, And there you have it..WHEEW!! Please give credit to the companies listed above..All I did was cut and past this info in an orderly fashion for you guys to read and enlighten your knowledge.


I am using DeLorme's MapExpert Version 2.0 for Windows, this version shows every little bend in the roads and rivers un-like a lot of map programs. It is CD based, but I have is on the HD of my notebook. It is the best that I have come across. This version also show many little side roads and even small roads inside some of the refinery plants I go to. It even has better maps of the plants then they have themselves. It will even show the roads to the oil wells here is Texas & New Mexico, and I know they are not on most mapping software.

And it will work with any GPS unit that has RS-232 DATA output in the marine format "NMEA", most if not all use this format as a default. I have tested about 10 different units and every one of them had the NMEA format. In the marine world they use the GPS in the NMEA format as part of the auto pilot system in many boats today.

I never leave home with out it.

...Allan Madar

I forgot to mention that if you are using a Laptop W/OUT a cd-rom and want to use the mapping software on your mobile..MICROSOFT Street Plus AND DELORME Map N Go 2.0 will not work w/out the cdrom..Meaning you cannot save the maps to your HD to call up on your Laptop. The programs mentioned above needs the cdrom.

But here are the products that do let you copy maps to your HD w/out having to use the cdrom..

Delorme Street Atlas 4.0 (newest version) ~$45
Delorme MapKit ~$495


For just everybody's general info, here are my opinions on the Garmin units we would be interested in. These are all 12 channel units and I am listing them in order of cost.

II+ - this is the bottom line for 12 channel units. It derived from the original "flippable" unit (II). The screen resolution and size is the bare minimum (100x160 ppi, 2.2"x1.5"). The antanna is little stalk that can be extended by coax.

12 - the reduced cost version of the 12XL. It can only use the internal patch antenna, i.e. no external possible. Same display as the II+ but with different screens. Not flippable.

12XL - the deluxe version of the 12 (actually came out before the 12). It has an internal patch antenna but can use the external antennas with the MCX connectors. Wide power input (10-40V) and a few other details.

III - Basically the same external design of the II+. Uses different navigation screens and has the interal road database. Same display. Flippable. Detachable antenna and using coax.

GPSMAP 175 - The largest handheld by far. It was the first along with the 12XL to use the 12 channel receiver. It uses differnet nav screens but the III is similar. It has built in global maps (very basic) but can accept the G-Chart cartriges for inland and offshore mapping (more detailed than the III maps). Internal patch antenna, can use external MCX antenna. Largest display and cleanest (3.4x2.2 and 160x240 dpi) display.

The 175 was the first 12 channel, then the 12XL, II+, 12, and now the III.

Opinions :

If you want to use these units in vehicle, you need an external antenna. With my softtop I can get away without one but it really helps. Mandatory for hardtops. The 175 and 12's can use the ultra low profile external antenna that has incredible gain. It is around 1.5x2.5x0.5 (lxwxh). The cable is very, very thin, maybe like 14 gauge wire. Much thinner than coax. With the other units, you can remove and extend the stock antenna with coax. There is also a separate external antenna available but as compact as the other one.

Screen size is important to see while driving :). Often overlooked is resolution also. This is kind of obvious.

Mapping-wise there is nothing as good as fugawi or delorme for moving map stuff but they require a laptop. The internal map stuff is great for highways so you might be happy with just the III. Off-road you are stuck with UTM/Lat-Long and a tmap. I just pick waypoints at home and download them into the gps and setup a route. Breadcumbing is also extremely useful and all of these units provide it.

You will be hard pressed to find more cost effective units. The 12 channel units are very nice and accurate. Fast to aquire and hold a signal very well. I strongly recommend that you be sure the unit is suitable for in vehicle use. Be sure to determine how portable you want to be. It is a secondary concern for me - I only want to move it from vehicle to vehicle. I have a separate GPS to carry around while hiking, etc.

Of course there are other models available. YMMV, etc.


>  I have been reading many of the notes regarding the Garmin III.  Any
>  thoughts on Alpine's CVA-1000.  Santa put an IOU for a GPS in my stocking,
>  needless to say I am looking before he (She) changes her mind! 

Both are great for the job the were intended to fill. The Garmin III is a $350 (store price) hand held unit that is tops in that field.

The Alpine must be mounted in some sort of vehicle and does not really reach great performance for a few days, super performance in about two weeks, and then continues to get to be slightly better for about two months when it is the tops. It is a GPS with a regional database, and two gyros. It is connected to some pulse generator at the cruse control, or the speedometer, which has NO calibration. It calibrates itself against the GPS. The GPS does most of the navigation, but the gyros and speed pulses contribute, and do dead reckoning when satellite signals are not receivable, say in a tunnel or underground parking structure.

Cost? About $1100 for the unit and one regional disk. About $500 for a display (I think it is about 6.1 inches), or hook it to the top of the line Alpine car stereo and it will use that display, which is about 5-1/2 inches as I remember. Both displays are fantastic. If you use it with the stereo, it can turn the music off or down, then announce turns.

The display can be modified to take a video input. This would work well for rear mounted cameras (a thread many months ago).

Look for the new Phillips Carin. It looks to be good too, though I hear it is $2500. Ordered with a new BMW, it is integrated with the stereo too. I don't know if it interfaces as an after market add on.

I love my Sony stuff. My lap top computer is a Sony, and the list goes on. As soon as I knew Sony made a unit similar to the Alpine, I grabbed my check book. The Sony is an orphan. It is being discontinued because of disappointing sales (I did not know it has been out for a year. No wonder sales have been disappointing.) It has a total US database, an optional databases for California plus Las Vegas, Florida, and Georgia. If you want one and you live in one of those three states, go for it, but since Sony bought the map company, it looks like new maps won't be available.


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