Real Time Kinematic GPS - Essay Example

Background Information GPS technology has been given enough consideration due to its usefulness and much advancement is there to get precise real-time positioning information till the cm level. Due to these advancements, the researchers and professionals are much at ease who are in need of high level precision of positioning data. The industry as a whole is revolutionized due to the advancements in this technology. Real Time Kinematic technique or RTK is a GPS mode that is broadly employed for accurate positioning applications. It was invented in 1990’s. It has several requirements such as a reference receiver placed at a base station and a roving receiver. Both of the receivers have their coordinates; the coordinates of the first reference receiver can be determined in a geocentric frame while the second’s in relation to the first receiver. The combined data of the two receivers is used by the mobile control device algorithms to work out the uncertainty of integers in order to calculate accurate positioning information. Wubbena, et al. (1996) informs that the precision and consistency of RTK solution reduces with adding distance from the reference station. Virtual Reference Station or VRS is a concept that is interrelated to RTK. The figure about the conceptualization of VRS indicates the reference stations of GPS, which work at a distance of seventy kilometres. There is a communication network established between the reference stations through which, data is transferred from one station to other. According to Higgins (2001), the data that is received on the central computer from reference stations results in the modelling of spatial errors due to which, the working of GPS is restricted. As far as users are concerned, they think that it is because of the roving receivers that transfer a mobile call to the central computer due to which, the position of GPS is approximated and corrections are demanded. After this processing, the central computer is able to make corrections on the basis of the coordinates of roving receiver and reference receiver. Justification In order to get more precise results and to make the value of dimensions much authentic and for the lessening of the problems due to which, restrictions are there in terms of survey of RTK, much improved impression of VRS survey is created. According to Cislowski and Higgins (2006), the VRS RTK technique is able to augment the productivity to nearly thirty to fifty percent. In addition, the time needed for procedures and people required for the jobs according to a human resource perspective are reduced due to which, much economical advantages are here. The competence of the field’s team is augmented and the time is safeguarded because of establishment of transportable stations and VRS RTK survey is responsible for it. Along with the above mentioned benefits, the VRS RTK survey also eradicates the requirement to establish a confined reference station and radio connection. Along with the previous improvements, during the RTK GPS, the surveyor is also in advantage because of elimination of safety threats. The surveyor has to be near the base station or appoint someone to be there along with the tools required so that the probability of any loss to the station is minimized. The urban areas face this kind of peril largely. For having a reference station each time, there can be a greater probability of errors due to which, base station is much more supportive in minimizing the possibility of errors. In addition, these errors sometimes are unable to be found out. For VRS RTK survey, one roving receiver is enough due to which, the costs involved in surveying are also lessened. All the described features add to the advantageousness of the VRS RTK. There is a restriction in terms of at most distance between roving receiver and the base station that is ten kilometres for RTK GPS. The restriction is imposed because of different categories of systematic errors, which can be there because of greater distance than ten kilometres. Wubbena et al. (1996) explains that because of the possible systematic errors, the results will be late and inaccurate to some extent. The range of ten kilometres is quite enough for surveying but where there are larger distances involved for surveying, there can be consideration of errors. RTS is networked for larger distances due to which, the errors are reduced and the survey is much precise and fast. The base stations and roving receivers lack an actual communication in terms of RTK GPS. There are restrictions in terms of the work of surveyor as he has to work in the boundaries of radio telemetry. Because of enhancement in mobile technology, this problem has been overcome. When an RTK survey is conducted, there are many causes of errors. Many causes of errors are eradicated by VRS technology. Nevertheless, the functioning of VRS with differently produced GPS receivers is still doubted. Ong at al. (2005) informs that this problem can be a hindrance in adoption and approval of VRS. GPS differential systems The information from the GPS satellite can be employed in different modes. According to Stone, et al. (1999), the ways that are adopted basically depend on employment of reference station along with a roving receiver and afterwards, the signals that are obtained at every receiver are assessed. Other ways depend on calculating wavelength and shifts, afterwards the results are calculated by getting the mean and squares and also the errors for positions are sorted out. Differential is a concept that is not understood clearly in terms of GPS. In Differential GPS, the errors are approximated from the received data by means of a permanent station. This information is sent as RTCM to other receivers. The data is collected in raw form from two receivers and is them calculated and contrasted in order to get precise data which is linked with Real Time Kinematics or RTK. The data that is received from different receivers needs to be compared and for this purpose, more than one satellite is required. The use of satellite can be limited, as, for measuring and comparing data, some satellites are used by the receivers mutually. Real Time Kinematic (RTK) GPS RTK surveying started in 1990’s. It is employed to discover the more precise data by dealing out the data from the reference receivers. Rizos and Han (2003) inform that not only the data is discovered but is also corrected. Nowadays, GPS is used with RTK as a tool for surveying. For the assemblage of real time data, the base station and roving unit, both are employed for a RTK GPS. The data that is received from the reference station is the output of the processing of computer along with roving receiver. For the purpose of finding positioning of data, RTK employs the carrier phase. According to Magellan (2009), RTK can be advantageous in terms of recompensing any delay, errors and problems with the GPS geometry. Due to this fact, the precision of data is augmented to a limit of centimetres. Mekik and Arslanoglu (2009) inform that due to the coding phase of GPS along with the carrier phase, much precise information about positioning is calculated as compared to code calculations. In addition, RTK also facilitates with differential corrections that help in getting much accurate positioning. To find much accurate results with Real Time Kinematic or RTK, five satellites should be employed minimally. This is regarded as a disadvantageousness of the system. However, with updated technology such as GLONASS satellites and GPS, five satellites can be tracked easily in all kinds of areas whether they are populated or not. The reference stations and roving stations, both have access to frequency receivers. El-Mowafy (2000) informs that reference receiver and roving receiver both are interconnected by means of radio equipment. Reference receiver contains radio transmitter while roving receiver contains radio modem. The roving receiver uses radio modem but this is different as compared to the radio modem used by Differential GPS. This radio modem revises the correction data in a time of 0.5 to 2 seconds. The density of information makes the reference receiver to augment update rate and this fact makes the RTK GPS to increase its competence till 2400 bytes per second. At least, a capacity of 9600 bytes per second is required. Langley (1997) informs that for this type of data transmission, VHF of UHF bands are required. Manufacturers of receivers make their receivers differently and they accept different formats. However, RTK GPS technique sends correction messages to roving receivers in the format which is accepted by different receivers. Hoffman (1997) informs that for eradicating the format disturbance, a standard format is available by the Radio Technical Commission for Maritime Services, Special Committee 104 (RTCM SC-104). Initially, the receivers are started and the first phase is called initialization procedure because it initiates the procedure. Afterwards, the phase of double differencing is there that is employed for calculation of wavelengths among satellite and receivers. The whole procedure is called ambiguity resolution and is described by Roberts (2005). These ambiguities need to be eliminated. After the elimination of ambiguities, the positioning till centimetre level is generated by the roving receiver that is connected to the receiver at the base station. The wavelengths are assembled from different satellites in order to eradicate the causes of major errors such as satellite bias. After the above mentioned procedure and initialization setup, the roving receiver is in motion and acts without any restriction for the assemblage of precise real time data. In case of any hindrance or problem, the initialization stage needs to be accessed again. After initialization, the receivers along with other equipment will continue to proceed towards their tasks. Limitations of Real-Time Kinematics (RTK) The limitations of Real-Time Kinematics (RTK) are recapitulated here in order to indicate the advancement of a system that is networked with reference stations. They are: Because of ascertainment and operations of GPS receiver and radio, which work by means of reference stations, there are concerns related to production, protection and precision issues. Because of the rover’s functioning at a distance of ten kilometres from the reference station, there can be augmentation of errors that depend on the detachment, which can be considered as a limitation. Telemetry communications are also ranged that can also be regarded as a limitation. Virtual Reference Stations (VRS) Cislowski and Higgins (2006) inform that VRS is the updated form of RTK technique and the purpose of this concept is to examine GPS and elevated accurate positioning. VRS reports that Global Navigational Satellite System or GNSS are reference stations are attached to the control centre by the use of modems. According to Landau et al. (2002), the GPS information is congregated from the reference stations and then modelled for by centre computer for the spatial faults. The control centre is informed about the actual location of the GPS receiver by means of a call. After this processing, corrections are made by central computer. Higgins reports that the roving receiver makes the algorithms comprehensive and they are placed in relation to the VRS. There are comparatively tiny baselines linking the VRS and roving receiver due to which, the doing of the VRS concept is made better. However, it cannot be said that because of distant physical stations, precision of positioning is debased. The precision of the corrections from VRS are made better by means of interruptions from the physical reference stations. How the VRS System Works The functionality of VRS system is as follows: For functioning of VRS system, network server connects at a minimum of three reference stations with the help of communication links. The roving receiver has a position of its own and this positioning data is sent to the control centre that is responsible for running the GPS network. For sending information related to Global positioning fixed data or GGA, mobile phone data links are employed. An example can be taken of GSM (Global System for Mobile Communication). Landau et al. (2002) informs that the reason for the taking up GGA layout is that it is accessible by almost all the receivers. After receiving data, the control centre responds by transferring correction information to the roving receiver by means of RTCM or Radio Technical Commission for Maritime Services after acquirement of correction information, the roving receiver calculates by means of differential GPS solution and after it, revise its positioning. The position comes out to be +1 or -1 meter precisely and this value is transferred back to the control centre. The control centre calculates the new RTCM corrections and transfers them back to the roving receiver by means of mobile data link. It looks as if the RTCM corrections are coming from the neighbouring station of the roving receiver. According to Landau et al. (2002), by the above mentioned technique, the probability of more precise and accurate positioning inside the GPS network is there. Read More