DIFFERENCES BETWEEN 2009 AND 2016 REVISIONS BASED ON COORDINATES IN GDM2000

The Geocentric Datum of Malaysia (GDM200) is realised with respect to International Terrestrial Reference Frame (ITRF) 2000 at epoch 2nd January 2000. In comparison with the 2000 frame, ITRF2014 has significant improvement in terms of its definition and realisation. Moreover, several great earthquakes that struck the Indonesian region for the past decades have deformed the tectonic plate, resulting in a shifted GDM2000. These earthquakes, followed by post-seismic activities, has caused GDM2000 to become obsolete. Following that, the Department of Survey and Mapping Malaysia (DSMM) has taken the initiative to revise the coordinate of Malaysia Real-Time Kinematic Global Navigation Satellite Systems (GNSS) Network (MyRTKnet) stations in GDM2000 into a new set of coordinates. Therefore, this paper presents an effort to analyse the differences between coordinates in GDM2000 based on 2009 and 2016 revisions. In order to measure the discrepancy, forty-seven (47) MyRTKnet stations in Peninsular Malaysia were chosen to estimate the differences between the two (2) revisions. The coordinates obtained from MyRTKnet stations were then projected into Rectified Skewed Orthomorphic (RSO) coordinate system to compute the differences in horizontal position and ellipsoidal height. The finding showed that the discrepancy ranges from 0.8 to 11.8 cm, with the smallest values at SETI station and the biggest value at KRAI station. Meanwhile, for the differences in ellipsoidal height, LIPI station has the biggest value of 8.1 cm, followed by the smallest value of 0.4 cm at SETI station. In conclusion, as the differences in revision gave impact on the changes of coordinates of MyRTKnet stations in Peninsular Malaysia, the frequent revision of GDM2000 should also consider the latest frame to give better positional accuracy, and a proper datum transformation (ITRF2014 to ITRF2000) need to be implemented for mapping purposes.

Comparative Analysis of Ellipsoidal Height and Shuttle Radar Topographic Mission Elevation

Ellipsoidal elevation represents a precise geospatial data type within the analysis and modelling of various hydrological and ecological phenomenon required in preserving the human environment. Likewise, Shuttle Radar Topographic Mission (SRTM) has created an unparalleled data set of global elevations that are freely available for modelling ubiquitous environmental applications. This research aims to carry out a comparative analysis of ellipsoidal heights and SRTM heights with the following objectives: downloading DEM’s (SRTM) data covering the study area, determining the spot heights within the boundary in conventional method, extract DEM’S heights within the boundary of the study area, and compared the heights in the conventional method with DEM’S heights. South GPS and Leica Total Station were used to acquire data for control extension and spot heightening respectively while the elevation of SRTM data was obtained by transforming the X and Y data from GPS observationto Longitude and Latitude before using ArcGIS 10.6 to extract the elevation of the boundary pillar and all the spot heights which were relatively compared in terms of its products- heights, contour, 3-D wireframe, 3-D surface model, and overlaid of contour on shaded relief. The results of the study showed that vertical difference using conventional method and SRTM dataset ranges between -2.345m to 11.026m. Also, the hypothesis tested using a two-tail student t-test and F-test revealed that one mean is not significantly different from the other at 95% confidence level. The research recommends that the products obtained for the two systems can be used interchangeably. Keywords: Shuttle radar topographic mission, Ellipsoidal elevation, contour, 3D wireframe, 3D surface model

Comparative Analysis of Change between Ellipsoidal Height Differences and Equivalent Orthometric Height Difference

Height is an important component in the determination of the position of a point. The study aimed at performing a comparative analysis of change between ellipsoidal height differences and the equivalent orthometric height difference of points. A hi-target Differential Global Positioning System (DGPS) was used to acquire GPS data with an occupation period of thirty (30) minutes on each point, which were processed using Hi-target Geomatics Office (HGO) software to obtain the ellipsoidal heights. An automatic level instrument was used to acquire leveling data, which were processed using the height of collimation method to obtain the orthometric heights. A total of fifty (50) points were occupied as common points for both the GPS and levelling observations at 20-meter intervals. The accuracy of the height difference was determined using standard deviation with the ellipsoidal height difference as 53.59cm and the orthometric height as 53.07cm respectively. A Root Mean Square Error value of 0.0621m was obtained as the accuracy of the change between the two height differences. Statistical analysis using the independent-sample Z test was used to analyze the data at a 5% significant level. The result shows no significant difference in the performance of the two height systems. It is worthy to note that GPS and spirit levelling height differences can be used interchangeably for any heighting in short distances for surveying and engineering applications.

Evaluation of ICESat-2 ATL08 Data Product: Performance Assessment in Inland Water

Advanced Topographic Laser System (ATLAS) instrument on-board NASA's Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) enabled the capability of detecting certain properties of the Earth's surface at a photon level. Primary applications of ICESat-2 are for cryosphere but extendable to measure and determine the changes in elevation for land terrain and canopy. ICESat-2 ATL08 data product is a level 3A product that contains the best fit height above a reference ellipsoid processed in fixed 100 m data segments, which typically uses more than 100 signal photons from level 2 product namely ATL03. In this article, ICESat-2 ATL08 has been evaluated for its accuracy. Accuracy assessment of a point ellipsoidal height can be done using known benchmarks or survey points. In the absence of known points, the performance of these points can be assessed by hydro-flatness test as well as by comparing the satellite observed surface water level with gauged water table height. Both these tests have been done on 5 large reservoirs in the Indian sub-continent. Hydro-flatness test on ICESat-2’s ATL08 data product determined the permissible variations that occur on the surface water body due to ripples, wavelets, and streaks at a centimeter-level. Water level from ICESat-2 data will be in ellipsoidal height and cannot be compared with gauged data as it gives the height of the water surface above an established altitude where the stage is zero, because of this we have compared the change of surface water level from different dates. The results indicate that the surface water levels from ICESat-2’s ATL08 data product are in line with gauged data at centimeter-level accuracy.

The Impact of Troposphere Correction for Designation of the Ellipsoidal Height of Aircraft at Approach to Landing Procedure

The paper reports on research into the effect of the troposphere correction on the accuracy of the vertical component determination of an aircraft’s flight as it approaches landing at Deblin Airport. The article presents ellipsoidal height value of the aircraft when the troposphere correction is considered in navigational calculations and when it is not taken into account. Accuracy of the aircraft positioning in the vertical plane using the SPP method is determined. The study shows that application of the troposphere correction in navigational calculations increases the accuracy of the vertical component determination by 25%–32%. The article and the study may serve as a valuable source of information for pilots, flight instructors and aircraft crews during training in operation and implementation of GNSS in aviation.

Accuracy Assessment of Aircraft Positioning by Using the DGLONASS Method in the GBAS System

The paper presents the accuracy results of aircraft positioning using the DGLONASS method in the GBAS augmentation system in air transport. In the research test, the coordinates of Cessna 172 aircraft were recovered on the basis of the DGLONASS technique. The calculations were executed in RTKLIB software in RTKPOST library in module “DGPS/DGNSS”. The raw GLONASS data from the onboard Topcon HiperPro receiver and also from the REF1 physical reference station were utilized in the research test. In the paper, the standard deviations of aircraft coordinates and integrity HPL and VPL parameters were presented and described. In the paper, the obtained aircraft coordinates from the DGLONASS method were compared and verified with the DGPS solution. For this purpose, the RMS-3D term and difference of ellipsoidal height of aircraft were estimated in the paper. The average value of RMS-3D equals to 1.71 m, however the difference of ellipsoidal height amounts to 1.46 m, respectively.

Analysis of Methods for Ellipsoidal Height Estimation – The Case of a Local Geodetic Reference Network

Ghana’s local geodetic reference network is based on the War Office 1926 ellipsoid with data in latitude, longitude and orthometric height without the existence of ellipsoidal height. This situation makes it difficult to apply the standard forward transformation equation for direct conversion of curvilinear geodetic coordinates to its associated cartesian coordinates (X, Y, Z) in the Ghana local geodetic reference network. In order to overcome such a challenge, researchers resort to various techniques to obtain the ellipsoidal height for a local geodetic network. Therefore, this paper evaluates, compares, and discusses different methods for estimating ellipsoidal height for a local geodetic network. The investigated methods are the Abridged Molodensky transformation model, Earth Gravitational Model, and the Orthometric Height approach. To evaluate these methods, their estimated local ellipsoidal height values were implemented in the seven-parameter similarity transformation model of Bursa-Wolf. The performance of each of the methods was assessed based on statistical indicators of Mean Square Error (MSE), Mean Absolute Error (MAE), Horizontal Position Error (HE) and Standard Deviation (SD). The statistical findings revealed that, the Abridged Molodensky model produced more reliable transformation results compared with the other methods. It can be concluded that for Ghana’s local geodetic network, the most practicable method for estimating ellipsoidal height is the Abridged Molodensky transformation model. Keywords: Abridged Molodensky Model, Earth Gravitational Model, Orthometric Height, Geodetic Network

A MATLAB GEODETIC SOFTWARE FOR PROCESSING AIRBORNE LIDAR BATHYMETRY DATA

The ability to build three-dimensional models through technologies based on satellite navigation systems GNSS and the continuous development of new sensors, as Airborne Laser Scanning Hydrography (ALH), data acquisition methods and 3D multi-resolution representations, have contributed significantly to the digital 3D documentation, mapping, preservation and representation of landscapes and heritage as well as to the growth of research in this fields. <br><br> However, GNSS systems led to the use of the ellipsoidal height; to transform this height in orthometric is necessary to know a geoid undulation model. The latest and most accurate global geoid undulation model, available worldwide, is EGM2008 which has been publicly released by the U.S. National Geospatial-Intelligence Agency (NGA) EGM Development Team. Therefore, given the availability and accuracy of this geoid model, we can use it in geomatics applications that require the conversion of heights. Using this model, to correct the elevation of a point does not coincide with any node must interpolate elevation information of adjacent nodes. <br><br> The purpose of this paper is produce a Matlab® geodetic software for processing airborne LIDAR bathymetry data. In particular we want to focus on the point clouds in ASPRS LAS format and convert the ellipsoidal height in orthometric. The algorithm, valid on the whole globe and operative for all UTM zones, allows the conversion of ellipsoidal heights using the EGM2008 model. Of this model we analyse the slopes which occur, in some critical areas, between the nodes of the undulations grid; we will focus our attention on the marine areas verifying the impact that the slopes have in the calculation of the orthometric height and, consequently, in the accuracy of the in the 3-D point clouds. This experiment will be carried out by analysing a LAS APRS file containing topographic and bathymetric data collected with LIDAR systems along the coasts of Oregon and Washington (USA).

Orthogonal distance from an ellipsoid

Finding the orthogonal (shortest) distance to an ellipsoid corresponds to the ellipsoidal height in Geodesy. Despite that the commonly used Earth reference systems, like WGS-84, are based on rotational ellipsoids, there have also been over the course of the years permanent scientific investigations undertaken into different aspects of the triaxial ellipsoid. Geodetic research has traditionally been motivated by the need to approximate closer and closer the physical reality. Several investigations have shown that the earth is approximated better by a triaxial ellipsoid rather than a rotational one Burša and Šima (1980). The problem of finding the shortest distance is encountered frequently in the Cartesian- Geodetic coordinate transformation, optimization problem, fitting ellipsoid, image processing, face recognition, computer games, and so on. We have chosen a triaxial ellipsoid for the reason that it possesess a general surface. Thus, the minimum distance from rotational ellipsoid and sphere is found with the same algorithm. This study deals with the computation of the shortest distance from a point to a triaxial ellipsoid.