South African Journal of Geomatics

Empirical investigations towards establishing a geoid-based vertical datum over South Africa

Matthews Siphiwe Mphuthi, Patroba Achola Odera — Tue, 04 Feb 2025 00:00:00 +0000

This study investigates prospects for establishing a geoid-based vertical datum in South Africa and aligning it with the International Height Reference System (IHRS) to modernise and unify vertical positioning. Employing the SAGEOID10 quasigeoid model alongside 138 GPS/levelling data points, this research evaluates the compatibility of spheroidal orthometric, normal, and orthometric height systems with the current quasigeoid and derived geoid models. The assessment is carried out using vertical datum offsets modelled at 100 and validated at 38 GPS/levelling points by applying a four-parameter planar model. The cross-validation results show that the normal and orthometric height systems provide a best fit, with standard deviations of ±5.1 and ±3.9 cm on quasigeoid and geoid models, respectively. The spheroidal orthometric height system referred to the land levelling datum (LLD) used over South Africa provided a better fit with the quasigeoid (±6.3 cm) than with the geoid (±7.6 cm). In addition, the study determined linear vertical datum offsets between the IHRS and variants of the local vertical datum (LLD, local quasigeoid and local geoid) on four tide gauge benchmarks (TGBMs) around South Africa. Empirical tests on a few benchmarks observed around each TGBM followed. The linear offsets at each TGBM, between each local height system and the global vertical datum (IHRS), revealed similar trends for the quasigeoid and geoid, but not for the LLD. The transformed heights (on the IHRS) were used to determine datum offsets based on benchmarks around each TGBM. Compared to the other three TGBMs (PEL, ELN and DBN), the results show the smallest mean offset around the TGBM in Cape Town. They also indicate that either normal or orthometric height systems should be adopted over South Africa and that the TGBM at CPT should be adopted when transforming a selected local height system to the IHRS.

Computational Vision in Photogrammetry for Georeferencing: Modern Resources Evaluation for UAV Image Processing

Henrique Lima de Sousa — Tue, 04 Feb 2025 00:00:00 +0000

Environmental Science aims to understand the world; this can be achieved by using geographic information systems (GISs). Also, georeferencing allows for the adjustment and alignment of raster data in combination with other GIS data. Thus, it is possible in terms of these techniques to interpret these types of data and their relationships, patterns, and trends. This study aims to investigate the use of modern engineering procedures, known as computational vision in photogrammetric image processing, as obtained from unarmed aerial vehicles (UAV). This is done via a small camera in the front of an embedded system and combined with proprietary software that uses computational vision resources. Although open-source software was the prioritized choice, the research began with a study on state-of-the-art computational vision algorithms and photogrammetry for drone inspection. The generation, processing, and verification of a set of photographic images were further procedures accompanying the study of the algorithms and photogrammetry which subsequently resulted in a georeferencing system. In fact, proprietary software employing computational vision resources was used in this study at the Universidade de Trás-os-Montes e Alto Douro in Portugal to compare it with the conventional methodology using modern computational resources to determine the benefits achieved. In conclusion, the positional quality of the generated georeferencing system was verified, and satisfactory results were reported. This underscored the potential of these modern computational resources in contemporary photogrammetry.

A web-based GIS application to optimize the customer onboarding for a utility company

Margaret N. Munywoki, Kaveer Singh — Tue, 04 Feb 2025 00:00:00 +0000

A web-based GIS application was envisioned to optimize Kenya Power and Lighting Company’s (KPLC) existing internal manual paper-based workflow process for new electricity customer connections in Mombasa County. The web-based GIS application was developed using the waterfall methodology which follows a sequential and systematic flow of processes. The web-based GIS application was named Jiconnect Web App. It could streamline the online customer registration process for power supply to their premises. Jiconnect was used to optimize workflow for onboarding new electricity customers. It was tested in various constituencies of Mombasa to ensure that it was functional and reliable. The potential integration of Jiconnect with existing internal manual paper-based workflow indicated that the web-based GIS application could benefit KPLC because it offered a cost-effective solution that saves time and resources.

Analysis of Spatial-Temporal Patterns of Wildfire Susceptibility in Queen Elizabeth National Park (QENP) - Uganda

Derrick Robert Irumba, Anthony Gidudu, Lydia Mazzi Kayondo — Thu, 06 Feb 2025 00:00:00 +0000

This study determined the variability of wildfire susceptibility in Queen Elizabeth National Park (QENP) in space and time. QENP is a protected area in Western Uganda. MODIS and VIIRS data for a six-and-a-half-year period from January 2015 - June 2021 were obtained to create an inventory of past fires. From these fires, spatial and temporal patterns were derived from exploratory spatial data analyses. The Weights of Evidence (WOE) method, a Bayesian form of statistical modelling, was used to determine the relationship between fires and wildfire conditioning factors, as well as to model wildfire susceptibility. Results of the study showed that the occurrence of wildfires within the study area vary seasonally. Sixty-one percent (61%) of the fires were observed to occur in the first dry season of the year, while thirty-one percent (31%) of the fires were observed to occur in the second dry season. Among the wildfire conditioning factors, altitude, vegetation (as measured by NDVI), and proximity to lakes indicated the highest correlation with the occurrence of fires. These conditions were attributed to physiographic influences, water stress in vegetation, and the socio-economic activities of the fishing villages around the lakes respectively. From the derived wildfire susceptibility maps, varying levels of wildfire susceptibility were determined. Proportional values of 19% and 20% of the study area were classified with very high and high susceptibility levels respectively. The remaining 61% of the study area was covered by moderate, low, and very low susceptibility levels. The study results provided vital findings about the seasonal patterns of wildfire occurrence, factors influencing the occurrence of wildfires and the locations most susceptible to wildfires. This information will enable managers to allocate fire management resources optimally to efficiently mitigate against wildfires within QENP.

Evaluation of recent Global Geopotential Models over South Africa

Matthews Siphiwe Mphuthi — Mon, 17 Feb 2025 00:00:00 +0000

This study evaluates the performance of three recent global geopotential models (GGMs) — WHU-SWPU-GOGR2022S, GOSG02S, and Tongji-GMMG2021S — over South Africa by comparing both height anomalies and free-air gravity anomalies derived from these models to data from 141 GPS/levelling points and 105,408 gravity data stations, respectively. The comparison method is crucial as it directly relates the model outputs to precise geodetic measurements, thereby providing a clear picture of model accuracy and effectiveness. Specifically, the Tongji model, developed using GOCE data, exhibited the smallest bias (3.9 cm), with a standard deviation of ±31,7 cm, thereby demonstrating the most accurate fit among the evaluated models with an RMSE of . Additionally, the free-air gravity anomalies comparison yielded biases of -1,74 mGal, -1,69 mGal, and -1,74 mGal for the WHU, Tongji, and GOSG02S models, respectively, with corresponding standard deviations around ±19 mGal. These comparisons not only validate the models against the established South African quasigeoid model, CDSM09A, but also highlight areas for potential refinement. The method employed enhances the contribution of the study to transitioning to a geoid-based vertical datum, thereby improving the accuracy of height and gravity measurements across South Africa and underlining the utility of these models in regional geophysical applications.