System RTK (Real-Time Kinematic)

is an acronym that is commonly used for the Determination of real-time position in a differential phase data, To realize its real-time guidance, reference station must transmit data phase and pseudorange it to users in real time using a certain data communication systems,
Reference station dam users must be equipped with the device transmitting and receiving data. Need dicata here that the type and specification of data to be delivered by a system for RTK reference station is given by the RTCM SC-104 format message type numbers 18,19,20,21, da 22 [RTCM SC-104, 1998].

In RTK system, the reference stations sending data menggunakansistem kepengguna with data communications operating in the frequency band VHF / UHF. For that generally required the direct visibility (line of sight) between the reference station and user, where the maximum distance (d).

Differential Positioning Method

Positioning accuracy in absolute terms described above, can be improved by using a differential positioning, the position of a point is determined (relative). In differential positioning, the position of a point is determined relative to other points of known coordinates (monitor station).
In the differential method, which is sometimes called a relative positioning method, by subtracting the data observed by the two GPS receivers at the same time, then some kind of error and bias of data can be eliminated or reduced. Elimination and reduction will improve accuracy and precision of data, and further increases the accuracy and precision of the position obtained.
In principle, using GPS location data the same observer with the data used to derive the results. Only in this case from the station reverensi a distance about 140 km is also used to apply relative positioning. that by simply applying the process of data reduction, position accuracy can not be increased dramatically, from 73.8 m (99%) to 7.2 m (99%).
In differential positioning, the types of errors and biases that can and can not be eliminated or reduced by the process of data reduction
The effectiveness of this reduction process depends on the distance between the monitor station de4ngan point to be determined position. In this case, the shorter the distance is the more effective the impact of data reduction, and vice versa. that the closer distance of the reference station (26 km rather than 140 km, the level of accuracy that diperolehpun position is getting better. Besides, it also appears that with more and more satellites are used (the better the satellite geometry) mak tingakat position accuracy obtained will also be getting better .
Finally it should be emphasized here that the differential is penenetuan position positioning methods should be used to obtain a relatively high position accuracy. Position accuracy can be given by a differential method Determination positions ranging from mm-level to the level of several meters.
Determination of the differential position can be applied as well as kinematic ststik using dat pseudorange and / or phase. The main application of differential positioning include mapping surveys, geodetic surveys, as well as middle and high berketelitian navigation. These methods are applied to survey with GPS today, seoerti starik method, static short, pseudo-kinemati, and stop and go, also based on the positioning method is difernsial.
In differential position determination, there are some applications that require real-time positioning information in an instant (real time). To serve these applications currently available are two systems commonly known as DGPS (Differential GPS) and RTK (Real Time Kinematic).
DGPS system is a system that is commonly used acronym for the system real-time positioning in differensialyang using pseudorange data. This system is generally used for positioning a moving object. To realize real-timenya guidance, the monitor station must submit a correction differnsial kepengguna in resl time using sistam certain data communications. This differential correction can be either pseudorange correction (such as RTCM SC-104) or correction of coordinates. In this case, a commonly used are the coordinates pseudorange.Koreksi correction is rarely used, because this correction requires that the sender reference station correction and the observers observe the same set of satellites, where it is generally not always dapt realized in the operational field.
Typical accuracy DGPS position diberikanoleh sisrem this is the range of 1 to 5 m. With that level of accuracy, DGPS system is commonly used in marine surveys.

Absolute Positioning Methods

Determination of the absolute position (absolute positioning) is a method of positioning the most basic of GPS was originally planned by the U.S. military to provide navigation services, especially for military personnel and their vehicles. This positioning method, the static and kinematic mode,
With regard to absolute positioning, there are few records to note are:

• This method is sometimes also called point positioning method, because positioning can be performed per    point without relying on other points
• The position is determined in WGS-84 system to the mass of the earth pust
• To determine the position of the GPS receiver requires only sister, and types of receivers commonly used for this purpose is the type of navigation or sometimes called a type of handheld (hand held).
• Points can be defined its position at rest (static mode) or in motion (kinematic mode),
• Accuracy of position obtained is very dependent on the level of data accuracy and geometry of the satellite.
• Main application of this method is for navigation purposes or other applications that require positioning information that is not too rigorous but available in an instant (real time), such as for purposes of reconnaissance and ground truthing.

Determination Method of the absolute position using pseudorange data on the basic principle is a method designed for determination by the management of GPS satellites (DoD, United States). In this case there are two levels of accuracy provided by GPS, which is called SPS (Standard Positioning Service) and PPS (Precise Positioning Service).
SPS is the standard of service provided by GPS in general to anyone at no charge, assuming the use of code-C / A. Given level of accuracy is the precision arrives been deliberately reduced by applying the wisdom of Selective Availability (SA). Typical position accuracy level given in this case is about 100 m (horizontal) with 95% confidence level. While PPS is dikhusukan service to the United States military as well as parties are permitted, through the use of P-code contained on 2 frekuens, L1 and L2. Besides, this PPS also has characteristics of anti-jamming (stronger signal), anti-spoofing, and free from the influence of SA. Given level of accuracy in this case is approximately 21 m (horizontal) with 95% accuracy level.
The level of accuracy can be dramatically improved by using differential positioning method (differential positioning) and also the phase of observation data.
In determining the absolute position on a epok using pseudorange, there are four parameters that must be determined / estimated as follows: • The parameter coordinates (X, Y, Z) • GPS receiver clock error parameter.
Therefore, to determine the absolute position on a epok using pseudorange data required minimum distance of four observation satellites fruit.
                         Accuracy parameter = DOP x Accuracy pseudorange
In the relationship above, DOP (dilution of precision) is a number that is used to reflect the power of a strong satellite geometry (both), and a great price DOP indicates poor satellite geometry (bad). Based on the estimated parameters, known for several types of DOP, namely:

 GDOP = Geometrical DOP (position and wakktu-3D),
 PDOP = Positional DOP (position-3D),
 HDOP = Horizontal DOP (horizontal position),
 VDOP = Vertical DOP (height), and
 TDOP = Time DOP (time).

Method Of Determining Position

Based on the mechanism of its application, the GPS positioning methods can be grouped over several methods, namely: absolute, differential, and real time Kinematic.

GPS Position Accuracy

Position accuracy obtained with GPS observations in general will depend on several factors namely:

• Quality GPS Receiver
• Number of satellites
• Old observations
• positioning methods used (absolute and differential positioning, Kinematic, etc.)
• Data Processing Strategy (Rial time & post processing, etc.)

Broad spectrum position accuracy provided by GPS is one of the beauty of the GPS, because GPS users have the flexibility in carrying out position determination in accordance with the required level of accuracy in an optimal and efficient (both time and cost). Therefore there is no doubt that GPS can serve quite a lot of applications, with diverse demands accuracy.

HOW GPS WORK?

Each satellite transmits two signals, namely L1 (1575.42 MHz) and L2 (1227.60 MHz). L1 signal is modulated with two pseudo-random signal that is the code P (Protected) code and C / A (coarse / Acquisition). L2 signal only bring the code P. Each satellite transmits a unique code so that the receiver (GPS devices) to identify the signal from each satellite. At the time of the "Anti-Spoofing" is activated, the code P will be encrypted and subsequently known as the code P (Y) or Y-code

GPS devices that are specific for only civilian to receive the code C / A on L1 signal (although in a sophisticated GPS devices can take advantage of the L2 signal to obtain a more precise measurement.

GPS devices receive signals transmitted by GPS satellites. In determining the position, we need at least 3 satellites for the determination of 2-dimensional position (latitude and longitude) and 4 satellites for the determination of 3-dimensional position (latitude, longitude, and altitude). More and more satellites are obtained, the accuracy of our position will be higher. To get these signals, the GPS device must be open space. If your GPS device we are in a room or a dense canopy and the area we are surrounded by tall buildings, the signal obtained will be further reduced so that it would be difficult to determine precisely the position or even not able to determine position.

Clasification GPS Segment

GPS (Global Positioning System) be devided in three segments 

1. Control Segment
Is the core of the GPS system that is satellite control stations are always doing the monitor to know the exact position, altitude, and speed of the satellite. The information was information was sent back to the satellite, and satellite will transmit information to receivers on earth. This control station operated by the United States Department of Defense.

2. Space Segment
The composition of the GPS satellites that transmit signals to earth, now there are 24 satellites NAVSTAR (Navigation Satellite for Time and Ranging) that orbited the earth and used for GPS.

3. User Segment
GPS signals from satellites used by the user on Earth to perform calculations in order to position a variety of purposes.

GPS Usage

GPS function when developed first is to determine the position and navigation but in line with the development of Geographic Information Systems (GIS), the GPS function increases with appearance information (data cupture), to present a picture and calculate the area of a form of specific features, and is a system information that can diakseske various GIS software.

The development of GPS is of course demands a certain uniformity for positioning and spacing system used in the geographic reference is used, in this case is WGS 84 (World Geodetic Survey 84) that is used now.

History

GPS is now used for a variety of purposes-some never even imagined by the makers of GPS. GPS can be used in almost all locations in the world except in places where GPS satellite signals can not be accepted, for example, inside buildings, inside caves, underground, and underwater.
GPS is actually a project the United States Department of Defense (USA) who gave the official name of the NAVSTAR (Navigation Satellite Timing And Ranging). The main part of the system is 24 GPS satellites orbiting the Earth at an altitude of 20,200 kilometers. Satellite orbit is designed so that every point on Earth can see at least four satellites at any time.
Each satellite orbit the earth approximately once in 12 hours with a speed of about 11,000 kilometers per hour. GPS satellites have panels solar power collectors to generate electricity it needs. There was also a battery that stores electric power and used it as a satellite does not get sunlight.
The first GPS satellite was launched in 1978 and the constellation of 24 satellites successfully completed in 1994. After that new satellites routinely launched to upgrade or replace old satellites Satellite damaged / not working anymore. Each satellite transmits navigation data in a signal of CDMA (Code Division Multiple Access)-same as the type of signal for CDMA cellular phone. CDMA signal using a code on the transmission so that the GPS receiver can still recognize the GPS navigation signals, although there is interference at the same frequency. The frequency used is the L1 (1575.42 MHz) and L2 (1227.6 MHz).
Information is transmitted from the satellite to a GPS receiver consists of two types. The first is called "almanac", ie the position of all GPS satellites. The second type of information called "efemeris", ie the almanac correction data. "If the 'almanac' is updated approximately once a week, the data 'eferemis' usually is updated every half hour. Instrument GPS receiver is switched on again after a day off can still use the almanac data before.

Introduction

Humans have long been trying to find a way to know with certainty the existence of (position) on the surface of the earth itself, where she was and where he would go. Humans have developed ways to determine its position on the surface of the earth from a simple way by using the signs of nature on earth, with a view to the position of the stars using a compass and some fairly sophisticated electronic perlalatan.

But these methods have yet to include many activities on the surface of the earth, and the accuracy of the resulting highly variable. The last system was developed human being is a GPS (Global Positioning System) which utilizes the position and the signals emitted by satellites orbiting in space and captured the receiver in the earth's surface.