|Akajiaku, C. C. and Onyeagoro, E., 2018.
|Improving Traverse Redundancy and Precision by Running on Double lines
|Good redundancy is required in measured quantities to isolate gross errors and improve the qualities of derived parameters. Improving the weak redundancies of traditional traverses by traversing on double lines is now possible with total stations which provide for less cumbersome measurements than previously possible and more so now that control traverses are computed by least squares adjustment using readily available computer software. Traversing on double lines requires some care in choosing traverse stations with inter-visibility to two immediately preceding and two directly succeeding stations from the instrument station. Traverses were run on double lines resulting in redundancy increase of seven per station. Local accuracy precision parameters improved also by as much as 25% and 52% with implementation at 30% and 100% of the traverse stations respectively. A chart that may be used to determine percentage number of traverse stations where traversing on double lines would be implemented to achieve set local accuracy improvements is presented. Key words: traverse, redundancy, precision, total station, control surveys, traversing on double lines, gross errors
|South African Journal of Geomatics,
|Vol. 7. No. 3, November 2018, pp. 372 – 383 DOI: http://dx.doi.org/10.4314/sajg.v7i3.13
|Akajiaku, C. C. 2018.
|A Method for Connecting Traverses to GNSS Controls Eliminating Troublesome Short GNSS Orientation Lines
|Global Navigation Satellite System (GNSS) surveys are used to establish long baseline control networks. Further breaking down of the controls are accomplished using total station traversing connected to the GNSS networks. Auxiliary stations are established at relatively short distances to each GNSS main station for traverse azimuth orientation. If the GNSS azimuth reference lines are short, the allowable uncertainties in the GNSS determined coordinates heavily encumber the accuracies of the azimuths derived from them. This is the problem with connecting traverses to GNSS controls via azimuth reference lines that are short. Reorientation traversing can solve the short GNSS azimuth reference line problem by running control traverses linked to GNSS controls without referencing the short GNSS azimuth lines. Four reorientation traverses of total traverse lengths of 1.4Km to 5.1Km were run between GNSS network stations to demonstrate the validity of the new method. A corresponding traditional traverse was run to compare with each of the reorientation traverse cases. Some t-distribution tests established that there were no statistical differences between the coordinates determined by the reorientation traverses and the corresponding traditional traverses coordinates at the 99% confidence level. P-value tests revealed that there were no significant probabilities of an extreme occurrence in which the coordinates from the two methods of traversing may be statistically different at the P < 0.01 confidence level. The research results thus show that reorientation traversing is a valid procedure that may be used to avoid the use of short GNSS reference lines.
|South African Journal of Geomatics
|vol. 7 No. 3 DOI: 10.4314/sajg.v7i3.7 November, 2018.
|Akajiaku, C. C. 2018.
|Outlier based selection and accuracy updating of digital elevation models for urban area projects
|Outlier based selection and accuracy updating of digital elevation models for urban area projects Akajiaku C. Chukwuocha Department of Surveying and Geoinformatics, Federal University of Technology, Owerri, Imo State, Nigeria. Received 4 June, 2018; Accepted 18 July, 2018 Continuing degradation of urban environments of developing economies results from failure to make decisions based on scientific methods that employ accurate digital elevation models (DEM) in modelling environmental phenomena such as flooding and erosion. Data dumping and wastage occur if fresh DEM are required for every new project ignoring existing data. Every DEM to be used for modelling may be accepted as is, updated or rejected for a new one based on outlier fitness tests. High cost DEM aged only a few months should also be tested since elevation changes could occur in very short periods. Older DEMs might still be useful if changes are only in limited areas which could be mapped to update the DEM, so saving cost. A DEM of Owerri, South East Nigeria created from a 1977 1/2500 topographic map series was evaluated using elevations of random Global Navigation Satellite Systems (GNSS) points resulting in a ±1.290 m root mean square error (RMSE). Outliers of the 99% certainty were traced to a heavily cut construction site and a topographical survey of the site was used to update the DEM improving RMSE to below the meter mark. Key words: Digital elevation model (DEM), geographic information systems (GIS), outlier, DEM updating, root mean square error (RMSE). INTRODUCTION The intelligent way to manage the urban environment in the 21st century requires making decisions based on results of modelling of environmental phenomena. Factors that ravage our environment such as flooding and erosion and the components that cause them can be determined long before they occur using the geographic information systems (GIS). Natural runoff routes of landscapes can be delineated on GIS platforms and constructions that would compromise them stopped in advance. Many of the surface flow induced environmental hazards require analyses that use the digital elevation *Corresponding author. Email: firstname.lastname@example.org. model (DEM) on GIS. Devastating floods and erosion of the urban environments of developing nations in West Africa continue to be reported, for instance in Karley (2009), Odufuwa et al. (2012), Aderogba (2012), Chukwuocha and AC-Chukwuocha (2014), and Reliefweb (2017). Much of these results from constructions carried out on unmarked runoff routes or ill-advised drainages. Availability of appropriate DEM fit for purpose is key in the analysis required to secure urban environments especially of the developing world.
|African Journal of Environmental Science and Technology
|Vol. 12, No. 8, pp. 258 – 267 DOI: 10.5897/AJEST2018.2519
|Akajiaku, C. C. 2018.
|Using Reorientation Traversing on a Single-Unknown Station or Multiple-Unknown Stations to Solve the Two-Point Resection (Free Station) Problem
|Traditionally, the two-point resection problem, which is coordinating an unknown station from which lines to two control stations and the included angle are measured without setting up on the control stations (free stationing), is accomplished by solving the triangle formed. There must be only a single-unknown station intervisible with the controls, otherwise the method fails. These limitations are overcome by the new reorientation traversing method by solving the system in a twofold traverse computation. The advantage is successfully coordinating desired single stations or when there is no intervisibility with either or both controls to set up on a few additional stations without setting up on the controls. Field observations were made on a single-new station with intervisibility to the two controls. In another case where the station desired to be coordinated was not intervisible with the two controls, two additional stations were also set up on without setting up on the control stations. A t-distribution test at 99 percent confidence level with a P-value test on the results proved the credibility of the reorientation traversing in solving both cases of the two point resection survey. The reorientation traversing is the only method known for resection survey of multiple-unknown stations in a lone network.
|Surveying and Land Information Science
|Vol. 77 No. 1 pp. 45 - 54
|Akajiaku, C. C. 2018.
|Taking Advantage of Propagation of Error Fractions in Survey Systems
|All information derived from survey measurements undergo processing through a set of specific computations. The errors in the measurements are transferred to the derived quantities through the process of propagation. Surveyors have always been trained to be cautious of propagation of errors. One to one propagation systems, are computational systems that are wholly additional in nature for example that in computing reduced levels from staff readings in spirit levelling exercises. Trigonometrical derivations are largely fractional in nature and may lead to better refined quantities than the observations if handled carefully. An example of deriving refined quantities from propagation of fractional errors is presented in a traverse exercise. It shows that the local accuracies and linear accuracies of such systems can be improved by a factor of about 2.
|Nigeria Journal of Geodesy
|Vol. 2 No. 1
|Osuagwu, J. C., Owakah, A., Chukwuocha, A. C. and Ibeje, A. O., 2017.
|Settlement Monitoring of Embankment Dams: Case Study of Tuatara Dam, North Central Nigeria
|Abstract: Embankment Settlement in earth dam is common at post construction. Settlement also occurs during construction where compaction of fill materials is below optimum level specified in the design. This study analysed post Settlement of Gurara Multipurpose Dam built on the Gurara River near Abuja, the capital of Nigeria. Seven monitoring devices such as Electrical Vibrating Wire Piezometers (EVW), Standpipe Piezometers, Relief Wells, Finger Drains, Differential Settlement Monitoring (DSM), V-notch and Concrete Block Tape Extensometer were used in Gurara Multipurpose dam. Data obtained from DSM devices was used in the settlement analysis. Ten year (2004-2014) data were obtained at seven control stations of the crest settlement data of the embankment. There are seven sections and each section comprises of three DSM devices, except section 22 which has only two. The dimensionless parameter known as settlement index (S i) and the percentage of the dam elevation P (%) that settled at each section were calculated for each of the seven sections. The measured difference in relative height P(field) and the calculated percentage of the dam elevation P(%) that settled at each section were plotted to ascertain the deviation limit of the dam crest. The study showed that the maximum value of the settlement index (S i) for each set of measurements at all sections was significantly lower than the threshold value of 0.02. Also the P (%) was less than 1% in all the sections indicating absence of creep or secondary consolidation of the embankment material.
|International Journal of Science and Engineering Investigations. Http://www.ijsei.com/papers/ijsei-67117-10.pdf
|Vol. 6 No. 71 pp. 66 – 72
|Akajiaku, C. C. 2017.
|Case studies of the reorientation traverse accuracy
|Abstract: The possibility of computing a traverse having no base angles at the takeoff and closing control stations has been previously published in Chukwuocha et al. (2017). In this computational method, the azimuth of the first traverse leg is indirectly determined between a pair of orphaned control stations without a field-observed reference azimuth line. The base angles at the control stations or the azimuth of the first traverse leg is computed from the geometry of the traverse. Thereafter, the traverse is computed as a normal traverse. This traverse method is termed reorientation traversing. This article will statistically compare the variation in the computed coordinates when using the reorientation traversing method versus the traditional traverse method, which has either known azimuths at each end of the traverse or two previously established control stations at the termini. To make this comparison, a series of four different traverses with varying numbers of new stations were run using both the reorientation and traditional traverse methods. From these case studies, a correctly weighted least squares adjustment was performed, and a statistical test at a 0.01 level of significance was performed on the resultant coordinates. This comparison demonstrates that the two methods produce a set of coordinates that can be considered statistically the same. The results demonstrate that reorientation traversing is a valid procedure when sufficient directional control is not available in the field.
|· Surveying and Land Information Science
|· Vol. 76 Number 2: pp. 107-117
|Chukwuocha, AC-N., Ngah., S. and Akajiaku, C. C. 2017.
|Vulnerability Studies of Sensitive Watershed Areas of Owerri South East Nigeria Using Digital Elevation Models
|Abstract: The impact of human activities on sensitive watershed terrains is a critical consideration in the management of urban ecosystems. Degradation of sensitive ecosystem features such as watershed land areas is often irreversible due to the extent and intensity. The vulnerability of 150m watershed management zone of Otamiri river Owerri Imo State, Nigeria was studied by topographic analysis using 1977 digital elevation model (DEM), 1977 aerial photos, Shuttle Radar Topographic Mission DEM of 2 000, 2012 satellite imagery and the 2016 Master Plan of the study area. The impact of human activities in elevation change was observed in the parts of substantial human activities while top graphical stability was recorded for areas of very low human activities.
|Journal of Geoscience and Environment Protectio, China.
|Vol. 5 pp. 1 – 10 · · DOI: 10.4236/gep.2017.510001
|Akajiaku, C. C., Elochukwu, C. M., Uzodimma, V. and Ono, M. N. 2017.
|Solving control reference azimuth problems of traversing using reorientation traversing
|Abstract: Planned traverse surveys encounter setbacks when control stations are orphaned without any intervisible neighbour. This matter is made more difficult if use of Global Navigation Satellite Systems or astronomic observations is not feasible especially in built-up areas or under canopies. A control azimuth problem exists in any such cases where there are only single control stations at one or both ends of a traverse scheme. The technique of "reorientation traversing" is a simple, time-And cost-saving technique that may be used to control the orientation of traverses between reliable control stations. The reorientation traverse begins and ends with setups on the point next after and last before the initial and closing control stations, respectively, sighting to the control stations but without setting up on the control stations. The rest of the traverse is run normally. A traverse run between two non-intervisible control stations, connecting five new stations over about 1.8 km was computed using the reorientation traverse technique and also with the traditional traverse technique. The linear accuracy results were 1/176,000 and 1/101,400, respectively, showing the feasibility of the new method. Some field exercises have shown that under certain conditions the reorientation traversing would give superior results compared to the traditional traversing.
|Surveying and Land Information Science
|Vol. 76 Number 1 pp. 23-37