Did you know that you can download free GPS maps – you will never get lost again and can visit all the hard to find Malaysian seafood places. If you have a car, you can even install a system that will read out directions for you through the car sound system. Your GPS can also be used when you visit other countries like Hong Kong, China, Japan and the U.S..
A good colour GPS Receiver from Garmin is about S$665 (US$365 from U.S., HK$3980 from HK).
Register and read the Wiki at this site for more information: http://www.malsingmaps.com
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Developed by the United States Department of Defence, GPS is officially named NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System). The satellite constellation is managed by the USAF 50th Space Wing. Although the cost of maintaining the system is approximately US$400 million per year, including the replacement of aging satellites, GPS is free for civilian use as a public good.
GPS includes a feature called Selective Availability (SA) that introduces intentional errors between 0 meters and up to a hundred meters (300 ft) into the publicly available navigation signals, making it difficult to use for guiding long range missiles to precise targets. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users.
SA typically added signal errors of up to about 10 meters (30 ft) horizontally and 30 meters (100 ft) vertically. The inaccuracy of the civilian signal was deliberately encoded so as not to change very quickly, for instance the entire eastern U.S. area might read 30 m off, but 30 m off everywhere and in the same direction. In order to improve the usefulness of GPS for civilian navigation, Differential GPS was used by many civilian GPS receivers to greatly improve accuracy.
During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in a decision to disable Selective Availability. This was ironic, as SA had been introduced specifically for these situations, allowing friendly troops to use the signal for accurate navigation, while at the same time denying it to the enemy. But since SA was also denying the same accuracy to thousands of friendly troops, turning it off or setting it to a error of 0 meters (effectively the same thing) presented a clear benefit.
In the 1990s, the FAA started pressuring the military to turn off SA permanently. This would save the FAA millions of dollars every year in maintenance of their own radio navigation systems. The military resisted for most of the 1990s, but SA was eventually “discontinued”; the amount of error added was “set to zero” in 2000 following an announcement by U.S. President Bill Clinton, allowing users access to an undegraded L1 signal. Per the directive, the induced error of SA was changed to add no error to the public signals (C/A code). Selective Availability is still a system capability of GPS, and error could be in theory reintroduced at any time. In practice, in view of the hazards and costs this would induce for US and foreign shipping, it is unlikely to be reintroduced, and various government agencies have stated that it is not intended to be reintroduced.
The US military has developed the ability to locally deny GPS (and other navigation services) to hostile forces in a specific area of crisis without affecting the rest of the world or its own military systems.
GPS allows accurate targeting of various military weapons including cruise missiles and precision guided munitions. The satellites also carry nuclear detonation detectors, which form a major portion of the United States Nuclear Detonation System. To help prevent GPS from being used in improvised weaponry, the US Government controls the export of civilian receivers. A US-based manufacturer cannot generally export a receiver unless it has limits on the velocities and altitudes at which it will report position and speed information. A general speed limitation of 515 m/sec applies and no GPS unit can function at an altitude of 18 kilometers or above.