| dc.description.abstract | Orthometric heights are important in all engineering surveying works to know how the terrain changes before setting out any structure for example roads and buildings, to obtain orthometric heights traditionally spirit levelling has been used but it is extremely costly and time consuming to perform in hilly, rugged, mountainous regions and over long distances so this study is carried out to assess the accuracy of Gnss data and classical terrestrial zenith angle method which is considered to be time saving and applicable, whether it can be used as a substitute of spirit levelling in determination of orthometric heights.
In this study, orthometric heights where obtained by two methods that is spirit leveling and Gnss data_classical terrestrial zenith angle along a profile of six points between two control points 71Y82 at Masanafu hill in Lungujja parish and 71Y85 at Lubya hill which is about 2.27622km. Gnss data _ Classical terrestrial zenith angle method was done by picking static observations using pro mark 800 receivers for two hours’ time plus measuring the zenith angle simultaneously and reciprocally using two total stations between each two neighboring points along the profile, afterwards processing was done using Trimble business center setting the required parameters then the heights obtained were 1201.046, 1178.485, 1182.345, 1189.435, 1180.051 and 1208.363.
Spirit levelling was carried out using an automatic level and ten temporally benchmarks where introduced carrying out forward and backward levelling to each benchmark starting from 71Y82 to 71Y85, an allowable linear misclosure was obtained of 0.003 and then distributed, heights obtained are 1201.046, 1178.496, 1182.355, 1189.443, 1180.06 and 1208.371.
Then heights obtained using the two methods were compared when they differ by 8-11mm with their root mean squares 1190.007 and 1190.014 respectively when appropriate measurement and processing strategies were applied. | en_US |
