 |
| GPS system |
Now, before we talk about GPS, lets try to do this simple task. Look at this picture :
 |
Assume that i stand somewhere in the red plane. The distance from where i stand to point A is 10 meters and to point B is 10 meters too. My question is, can you locate me at that red plane ??
Can you answer that ??. of course you do. But if you don't, here is the answer.
What you should do is to draw a circle with radius 10m from point A. Then you draw second circle with same radius from point B. You can see that the two circles will intersect at two points, P1 and P2.
From the above picture, can you tell me, which is the exact position where i stand, is it at P1, or at P2???. You are correct, it is at P1 since only P1 that lies on the red plane.
The GPS stands for Global Positioning System. It is a way of locating a receiver in three dimensional space anywhere on the Earth, and even in orbit about it. To locate the receiver position on earth is done by the same logic with locating point in plane just as we discuss above.
For two dimensional plane, we need at least 2 circle to locate the point and we have to choose one point to be the exact location from two possibility points. For three dimensional space, at least we need 3 sphere to locate and choose one point to be the exact location from two possibility points. Because The GPS using satellite as the marking point, therefore we need at least we need 3 satellite to locate a point on earth.
So, we need to know what is the distance from those satellite to the point where we set the GPS on. The GPS receiver figures the distances by analyzing high-frequency, low-power radio signals from the GPS satellites. Better units have multiple receivers, so they can pick up signals from several satellites simultaneously.
Radio waves are electromagnetic energy, which means they travel at the speed of light (about 186,000 miles per second, 300,000 km per second in a vacuum). The receiver can figure out how far the signal has traveled (the distance between GPS and satellite) by timing how long it took the signal to arrive. Now, we see that the accuracy of the GPS is dependent on how good the quality of signal is.
There are some problems which influencing the signal quality:
- GPS Satellite drift;
- GPS “Multipath” Signals (false signals that are generated when a true signal bounce off the ground or nearby structures).
- GPS Signal Refraction of the radio waves as they go through the earth’s atmosphere
- Radio and other interference
Those problems have caused the accuracy of ordinary GPS. There’s a huge difference between knowing where you are within 30 feet (10 meters) and knowing where you are within ¼ inch (6mm). You can buy an inexpensive, handheld GPS receiver that will provide location information within a horizontal tolerance of ±30 feet (10 meters). However, a GPS system that can provide accuracy to within ¼ inch (6mm) requires much higher sophistication and a much larger investment.
That for the GPS theory, now lets see about GPS History
The GPS project was developed in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including a number of classified engineering design studies from the 1960s. GPS was created and realized by the U.S. Department of Defense (USDOD) and was originally run with 24 satellites. It became fully operational in 1994.
Now, we may compare, with the Crop Circle phenomenons and 'Man Made GPS'. And from comparing these two phenomenon it seem that these two things are not correlated. In other word, the GPS (Man Made GPS) had not involved in any of crop circles creation.
But, i truly believe that the creation of smart Crop Circles are being made by the aid of the tools which had the same principle as the GPS, our GPS.
No comments:
Post a Comment