Explain clearly the meaning, characteristic and purpose of: a) GDM2000 b) myRTKnet c) standard deviation
a) GDM2000 (Geocentric Datum of Malaysia) Malaysia) Meaning:
In Peninsular Malaysia, our earth-centred coordinate datum is the regional datums of Kertau 1948 in Peninsular Malaysia and Timbalai 1948 in Sabah and Sarawak. So, GDM which stands for the Geocentric Datum of Malaysia will forms the new earth-centred coordinate datum for Malaysia .GDM2000 is basically realized using Global Positioning System (GPS) to connect the national Zero Order Network (i.e. the Malaysia Active GPS System stations) with some of the global permanent GPS network (i.e. the International GPS Service stations). GDM2000 was officially launched on 26 th of August 2003. A geocentric datum is a geodetic reference frame that uses an ellipsoid that has the earth¶s center of mass as its origin. The size and shape of this ellipsoid closely approximates the size and shape of the earth. The main advantage is that GDM2000 coordinates are immediately compatible with global coordinates obtained from GPS and with other coordinate systems adopted in many parts of the world. It will also allow an efficient exchange of data and linking of products from various information systems. Characteristic:
The main advantage of GDM2000 is, coordinates are immediately compatible with global coordinates coordinates obtained from GPS and with other coo rdinate systems adopted in many parts of the world. It will also allow an efficient exchange of data and linking of products from various information systems. Before satellite techniques were available long long ago, t he existing coordinates were obtained using conventional techniques. They are based on a model of the earth, that best best suited our our regio regio n at the time. time. But it is a bit different different with GDM2000,it GDM2000,it is based on an international mathematical model which "best fits" the shape of the whole earth, with its centre coinciding with the earth's centre of mass. Existing coordinates will change approximately 200 metres with the new GDM2000. The exact change and orientation of the change will vary slightly from area to area
One of the motivating factors in the adoption of the GDM is to develop the cadastral database to be in an internationally accepted reference frame and to an acceptable and defined accuracy. The bearing as well as distance of the land parcels and consequently the lot boundaries will not change . However, the coordinates of the boundary marks will change since they would then be referred to a different coordinate referencing system. Nevertheless, the present cadastral survey system will be maintained until the full implementation of the Coordinat ed Cadastral System (CCS), which would be making use of GDM2000 as the coordinate reference frame in Peninsular Malaysia.
Purpose:
There are many reasons for the adoption of GDM2000. Amongst them are: · · · ·
Wide spread use of satellite positioning sys tems Existing datums not compatible Unification of datums between East and West Malaysia In line with international recommendation
b) myRTKnet (Real-Time Kinematic) Meaning:
MyRTK network is an effort to use real-time survey technology for the enhancement of many services and dissemination of various geodetic products Real-Time Kinematic (RTK) is now widely used for surveying and other precise positioning applications. The classical RTK technique requires tha t GPS data be transmitted from a single base receiver to one or more roving units. Characteristic:
RTK can provide centimeter position accuracy, but the accuracy and reliability of the standard RTK solution decreases with increasing distance from the Base Station. This limitation on the distance between the roving GPS receiver and the RTK Base Station is due to the systematic effects of ephemeris, tropospheric and ionospheric errors. These systematic errors result in reduced accuracy and increasing initialization time as the distance between base and rover increases. Besides the aforementioned constraint, the limitation is also due to the range of available radio telemetry solutions. In practice, this means that a temporary RTK Base Station must be established close to the work area, often at a location that does not provide any physical security or continuous power supply. Each time such a temporary reference station is established, there is a likelihood of introducing an error in the reference station coordinates that will be transferred into the position calculated by the rover RTK receiver. Such an error can easily go undetectedwhen using a single base station. The physical communications infrastructure is provided by the IPVPN over COINS frame relay system. This system works by connecting any respective site into the Telekoms Malaysia frame relay network. The service is available throughout Malaysia except for some isolated locations. The advantage of using IPVPN verses point to point leased lines is that IPVPN will require only a single high speed connection and modem at the Central Control rather than a connection comprising of a modem and separate leased line for each station. Purpose:
i.
To establish a network of permanently running GPS base stations, at a spacing of 30 to 150 km, feeding GPS data to a processing centre via frame-relay IPVPN communication network. ii. To establish a central facility that will model the spatial errors which limit GPS accuracy through a network solution and generate correct ions for roving receivers positioned anywhere inside the network with an accuracy
better than a few centimeters (dense network) to a few decimeters (sparse network) in real time.
ii.
iii. To establish a web site that will make available near real time (1 - 3 hours) reference station data to the users for post -processing differential GPS throughout the coverage area. The primary goals in designing the system were for efficient and easy operations, facilitate user understanding of the network and for expandability. Some empirical numerical limits have been suggested for IP addressing and efficient operation of the system. The networking protocol used is the Internet Protocol (IP). Though contained in a single private network, the system was split into 2 subnets which is not representative of classical IP subnet class. As such this network is considered as µclassless¶. Each subnet consists of all reference stations and the Control Center (also referred to as central control or CC).
c) Standard deviation Meaning:
A measure of the dispersion of a set of data from its mean. The more spread apart the data, the higher the deviation. Standard deviation is calculated as the square root of variance. It is a statistical measurement that sheds light on historical volatility. For example, a volatile stock will have a high standard deviation while the deviation of a stable blue chip stock will be lower. A large dispersion tells us how much the return on the fund is deviating from the expected normal return s.
Characteristic:
The standard deviation is a statistic that tells you how tightly all the various examples are clustered around the mean in a set of data. When the examples are pretty tightly bunched together and the bell -shaped curve is steep, the standard deviation is small. When the examples are spread apart and the bell curve is relatively flat, that tells you you have a relatively large standard deviation.
Purpose:
. To understand this concept, it can help to learn about what statisticians call normal distribution of data. A normal distribution of data means that most of the examples in a set of data are close to the "average," while relatively few examples tend to one extreme or the other
