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GPS and the Garmin-GPS-receiver
WHY BUY A GPS FOR HIKING?
I have owned a Garmin-GPS-Receiver and have been sailing offshore with it for years and using it to help me navigate. The word is help, it is an aid, and a GPS is no substitute for proper detailed maps and compass and knowing how to use them. They can give you an accurate and instant position in rough country. They can be used to help you navigate to a waypoint, such as trail or river, or planned camping spot. You can program in routes to follow and at each waypoint you can It will give you distance to go, speed over the ground, estimated arrival time at your current speed and compass bearing to your waypoint. Of course you will need a map to show you the mountain or ravine that stands between you and the camp. The Garmin-GPS-Receiver also has a handy function called a Sun and Distance Calculator and you will get sunrise and sunset if you program in two waypoints.
Having had several Garmin-GPS-Receiver units I now have the eTrex Vista® C Garmin-GPS-Receiver as it is small with easy to see color screen, automatic routing, a much increased battery life. The Magellan 315 is also good. So whether you choose a Magellan or Garmin-GPS-Receiver it can add an interesting new dimension to your hiking
WHAT IS GEOCACHING? The latest GPS use is Geocaching or Stash-hunting and is literally a high tech adventure and treasure hunting game. What happens is that people and organizations setup caches around the globe and share these locations on the internet. The GPS user then uses the waypoint coordinates to find the cache, so you hike or find the cache using your Magellan or Garmin-GPS-Receiver, enjoy the journey and then: 1. When you locate the cache you should add an item 2. You can take an item from the cache 3. You record your visit in the cache logbook 4. Replace the cache in the same position and condition you found it Magellan sponsors and supports local, national and international playing fields. This year, they are holding the 3rd geocaching contest in the United States and will introduce the contest in Germany for the first time. The Magellan BE THERE™ GPS Adventure is scheduled for 30 cities in the US and five in Germany, beginning on May 23, 2005. Anyone can register on the Magellan website to access the clues and coordinates, and then head off with their handheld GPS to search for the cache containers. Check out www.Geocaching.com and www.Navicache.com How serious is this game? There are now some 167818 active caches in 215 countries and expanding.So get your Magellan or Garmin-GPS-Receiver out, backpack and boots and have some fun
WAT IS GPS? GPS means Global Positioning System and for hiking the handheld Garmin-GPS-receiver is a favorite. The US Dept of Defense (DOD) operates what is called the NAVSTAR system. The system consists of 28 satellites inserted into six polar orbits so that at least four satellites will always be visible above the horizon at any time. GPS position fixing involves trilateration (often called triangulation) of position derived from a number of satellites; satellite ranging to measure the distance from the satellites; accurate time measurement; the location of all satellites and correction factors for ionosphere conditions. When you power up your Garmin-GPS-Receiver this is what happens: 1. When you power up the Garmin-GPS-Receiver it initializes with the closest satellite and ephemeris data is downloaded into memory. A period of at least 20 minutes is often required to stabilize a position at initial startup and verify the status of satellites, availability etc. When you switch off a GPS, the last position is retained in memory. If your position remains within 50 miles, prior to the next power up, your position will generally be available within approximately 3-5 minutes. 2. The GPS receiver monitors for data from all other satellites in view. Based on this data it locks on to a satellite signal to commence the ranging process. 3. Based on the data on positions and times the receiver calculates a position with respect to the positions of satellites. Normally this will be displayed to two decimal places. Some units give three decimal places, but such accuracy is highly suspect and should be treated with caution.
What is Wide Area Augmentation System (WAAS) The system operates by a ground base calculated ionosphere differential correction signal being uploaded to a satellite and rebroadcast back again to WAAS enabled Magellan or Garmin-GPS-Receiver. Accuracy is typically around 3m against 10m.
How Accurate is GPS GPS accuracy has been the subject of widespread debate and controversy over the years. Precise Positioning Service (PPS) This service is primarily for military use and is derived from the Precise (P) code. PPS fixes are generally accurate within 16 meters spherical error. Standard Positioning Service (SPS) This service is intended for civilian use and is derived from the Course and Acquisition (C/A) code. Accuracy levels are within 141 meters 95% of the time. Also many hikers are changing altitude all the time and this imposes errors and for real accuracy you will have to punch in the exact altitude from your map What is Selective Availability (SA) This is the process of intentionally degrading positional accuracy by altering or introducing errors in the clock data and satellite ephemeris data. SA is characterized by a wandering position, and often a course and speed over the ground of up to 2 mph while actually stationary. SA has been officially switched off and the US says they will not re-impose it, but you all believe that, right? And it is possible to be activated in times of defense emergencies. What is Horizontal Dilution of Position (HDOP) GPS accuracy quality is quantified by what is called (Geometric) Horizontal Dilution of Precision (HDOP), which indicates the dilution of precision in a horizontal direction. The cause is poor satellite geometry, which is due to poor satellite distribution. It is generally measured on a scale of one to 10. The higher the number, the poorer the position confidence level. What are Chart Datum Variations In the United States, 3 chart datums are used and these are the NAD 27 (North American Datum 1927); the NAD 83 (North American Datum 1983) and the WGS 84 (World Geodetic System 1984). WGS 84 is the default standard. What can Affect GPS Accuracy? The GPS is often considered as absolutely perfect but this wrong, and they have inherent errors that decrease accuracy. These errors are in addition to the HDOP and SA factors previously described. GPS Clock Errors Each GPS satellite has two rubidium and two cesium atomic clocks. These clocks are monitored against terrestrial atomic clocks. Based on this information, the entire GPS system is continually calibrated against UTC. Ionosphere Effects Like radio signals, both ionosphere and troposphere conditions can affect GPS accuracy. Errors occur in signal transmission times that can impose signal propagation delays. This signal refraction introduces timing errors that cause positional inaccuracies. Like radio propagation it alters given changes in atmospheric conditions etc. Errors can be as great as 20-30 meters during the day and 5 meters at night. Space Weather such as solar activity can really affect things. Multipath Effects This occurs when signals from a satellite traveling to a receiver arrive at slightly different times due to reflection or alteration. The effect is that positions may be derived off the “bad” signal, resulting in an inaccuracy. Satellite Integrity If the signal being transmitted from a satellite is corrupt due to a malfunction, it will have subsequent effects on position computations and solutions.
WHAT GPS SHOULD I BUY?
Multiple-channel units are now virtually standard. This powerful processing capability enables the monitoring and tracking of up to 12 satellites and the parallel processing of all those satellites in view simultaneously. These units increase position accuracy, reduce errors, and improve the HDOP. I have a Garmin-GPS-Receiver and have been using one while sailing for years. They are very cheap and a basic unit costs just a $100, but if you go for color display with full mapping capability the cost will rise to around $400-$500. Unless you really understand coordinates and positions choose a Map screen. Choose the largest memory you can afford although most are more than adequate. Most also have sufficient route capability and waypoint storage up to 500 points, that is more than enough. Check the screen readability, color can be hard in sunlight although new screen types are overcoming this. The Garmin-GPS-Receiver Model eTrex Vista C incorporates a barometric altimeter and an electronic compass. It also has 256-color, sunlight-viewable display. Also there is automatic route generation, off-route recalculation, turn-by-turn directions with alert tones, and icon-driven menus for finding points of interest and this is when you use Garmin’s optional MapSource® CD’s. It also has a Mini-USB port for downloading of map data from the Garmin library of optional MapSource CD’s using a PC. It is also WAAS-enabled if the area has coverage
The Garmin-GPS-Receiver Model GPSMAP 60 This a lower cost unit with a sunlight-readable, four-level grayscale display. It claims 28 hours of battery life and has serial and USB connections for downloads. It also has a base-map with automatic routing capabilities along with 24 MB of internal memory For those that want some extra functions it also incorporates geocaching and geolocation gaming modes for extra entertainment. Other features are an alarm clock, sunrise/sunset and moon phase tables, optimal hunting and fishing times, etc The Magellan eXplorist 400 This features optional secure digital (SD) cards. Load up topo or lake maps using the optional Magellan MapSend® software*. It has a high-speed USB data port for downloading information. It also has Geocache Manager software to assist in the download of cache data directly. Also 8 MB of built-in maps and 8 MB of internal memory to save 5 track log files, 20 routes and 500 points of interest, and you can save as many as you need to optional SD cards. It is just 2.2 in by 4.7 in and weighs in at 5.4 oz. Power comes from a Li-Ion Rechargeable Battery which can power for up to 17 hours. The TrueFix GPS technology uses 14 parallel channels, supported by WAAS and EGNOS Satellite-Based Augmentation Systems for fast signal acquisition, minimal signal loss and reliable accuracy to within 3 meters. The Geocache manager allows downloading of coordinates direct from Internet sites
Help! My GPS is Not Accurate Large Fix Error The GPS system may be down, or a satellite may be shut down. SA may be activated, or the HDOP may simply be excessive due to poor satellite geometry in your location. Small Fix Error Errors that are not significantly large but consistently outside normal accuracy levels are attributable to a number of sources. The signal may be subject to an excessive amount of atmospheric disturbances, such as periods of extensive solar flare activity. Make sure your aerial orientation is vertical, that means hold the receiver vertically. No Fix This is often caused by loss of a satellite view or when a satellite goes out of service. If you have severe shadowing in a gorge or gully, this will shadow signals, as will mountains and waterfalls. Get into clear space and check again. Also beware that walking in thick forest, or under a dense tree canopy will affect accuracy and signal Data Corruption The most common cause of data corruption is that caused by “fingers.” Has another person on your group unfamiliar with operating the GPS altered configuration parameters such as time settings or altitude? What About Mapping System? Some Garmin-GPS-Receivers and other manufacturers incorporate dedicated map that are generally unique to the manufacturers. This means you cant interchange a Magellan program to a Garmin-GPS-Receiver one. You need to look at what each offers for the area you are going to. Handy Garmin-GPS-Receiver Hints The GPS run on batteries, take a spare or two. In fact why not just switch the GPS on every 2 hours and check your position and save battery life. Don’t drop them as they will get damaged. Don’t leave it sitting in the hot sun, your Magellan or Garmin-GPS-Receiver electronics don’t like excess heat.
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