An Alternative Choice in Heighting

Abstract

Comparison of orthometric heights obtained from the combination of GPS/Levelling survey method with that obtained from Lidar, Srtm, and Astergdem data is an area of research which is of great interest to Geomaticians. This area of research makes possible the discovery of other suitable methods of determining orthometric height which can be selected for use depending on the region, extent and nature of the terrain where the project is to be executed.The X, Y, Z coordinates and the geoidal heights for all the existing controls within university of Lagos were determined using the GPS/ Levelling survey method, the required orthometric height (H) was then obtained as the differences between ellipsoidal and geoidal heights. Extracting orthometric heights for the X and Y coordinates of observed control points overlaid on each of Lidar, Srtm and Astergdem required the use of spatial analysis tool in an arc map environment. From the profile plot (Figure 3.5) of all the orthometric heights, the heights relationship was easy established. From the descriptive statistics test (Table 3.4), the one way ANOVAs test at 1% and 5% level of significance (Table 3.8), the number of points in other methods whose orthometric height is closed to that of Levelling/GPS method (Table 3.7) and correlation test on the various orthometric heights obtained (Table 3.5) it is obvious that all the applied methods operates at different spatial resolutions, of all the four methods, GPS/Levelling method was the most reliable and most accurate method followed by lidar method, then by astergdem method and Srtm has the least. In a nutshell, Orthometric heights generated by method of Lidar are very close to that generated by GPS/Levelling method at several stations, thus method of Lidar was considered as the most suitable alternative to GPS/Levelling method, whenever the use of later method cannot be easily accomplished.