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.

A GIS-based approach to analyse potable water accessibility in Langeloop village in Ehlanzeni District Municipality, Mpumalanga, South Africa

Knowledge Mathaba, Peter Schmitz — Fri, 21 Mar 2025 00:00:00 +0000

Access to clean potable water is a fundamental human right for sustaining life and well-being. However, in rural areas, people struggle to find enough clean water to cook and drink; they travel or walk long distances to access potable water. Langeloop settlement is a rural area that struggles to access potable water. Therefore, this study aimed to analyse potable water accessibility in the Langeloop community to identify underserved areas using a GIS-based approach. Langeloop settlement consists of the 11 sections/extensions used in this study. The mixed methods research approach was used, and data regarding potable water sources such as standpipes were captured using a GPS device, while a questionnaire was used to conduct a survey. Service area network analysis was performed on the standpipes data. The findings of the study are that water accessibility is below average, with many households still having no access to potable water. The study further proposes an expansion of the current standpipe system to improve access to safe drinking water. This study also found that water availability is a more prominent problem than proximity to a water source. Hence, one of the observations of this research is that most residents would prefer water availability to be highly prioritised in a quest to improve water accessibility in the Langeloop settlement. Further objectives of this research are to reflect on the importance of resource allocation and targeted interventions to improve water accessibility for communities in need.

Assessing the impact of COVID-19-induced lockdown on land surface temperatures in heterogeneous cities

Fri, 21 Mar 2025 00:00:00 +0000

Urbanisation has brought about significant changes in the land use/land cover (LULC) and land surface temperatures (LSTs) of cities. The impact of the COVID-19 lockdown on LSTs in Polokwane and Johannesburg, South Africa, was analysed over the years 2020 to 2022, using Landsat 8 and 9 images. The relevant LSTs were retrieved by applying the temperature/emissivity separation algorithm. The normalized difference built-up index (NDBI) and the normalized difference vegetation index (NDVI) threshold techniques were used to evaluate the LSTs for the two cities in terms of five LULC classes: bare land, built-up area, road, vegetation, and waterbody. The LST patterns were estimated per LULC class and the Pearson’s correlation analysis was performed to examine the relationship between NDVI, NDBI, and LST. The findings revealed that throughout the lockdown period (i.e., from January 2020 to March 2021, there was a decrease in LST values across all LULC categories − by 1°C for vegetation and 2°C for the bare land, built-up, road and waterbody classes. The LST values showed an increase from 2021 (during lockdown) to 2022 (post-lockdown), thereby demonstrating in particular their association with the bareland class, where the most notable increases of 1.9°C and 0.6°C were observed in Polokwane and Johannesburg, respectively. There were strong negative correlations between the NDVI and LST (i.e., -0.62, -0.58, and -0.71 for Polokwane and -0.69, -0.69, and -0.73 for Johannesburg) in 2020, 2021, and 2022, respectively. Strong positive correlations between NDBI and LST (i.e., 0.81, 0.79, and 0.85, and 0.70, 0.59, and 0.77) were recorded in Polokwane and Johannesburg respectively for the same period. The decline in LSTs was due to the cessation of industrial activities, transportation, and other human activities, resulting in improved air quality that in turn reduced the effects of the respective urban heat islands (UHIs). The findings offer valuable information that is vital for decision-making procedures that are in line with the aims of SDG 11 which are to improve the sustainability of cities.

Geospatial data quality training for the South African Spatial Data Infrastructure – Lessons learnt from training geospatial data custodians

Antony K Cooper, Serena Coetzee, Marinet Blom, Maroale Chauke, Vutomi Ndlovu — Fri, 21 Mar 2025 00:00:00 +0000

Standards play an important role in achieving the objectives of a spatial data infrastructure. However, standards can be difficult to understand and implement for those with limited exposure to them. The South African Spatial Data Infrastructure (SASDI) aims to facilitate the capture, management, maintenance, integration, distribution and use of spatial information. To decide whether a SASDI data set is fit for a specific purpose, users need information about its quality. SANS 19157:2014, Geographic information – Data quality, specifies how the quality of geospatial data can be described and assessed. The Committee for Spatial Information (CSI), responsible for implementing SASDI, identified the need to train geospatial data custodians in implementing SANS 19157. While custodians were eager to learn, several barriers prohibited presentation of training in a ‘traditional’ classroom setting. These barriers included the costs and time to travel from remote areas of the country to a training venue and challenges with scheduling the training at a time suitable to all participants. Online training was therefore delivered − however, structured in a way to overcome general ‘online fatigue’ after the pandemic. In this paper we present our experiences in presenting training on SANS 19157 to professionals responsible for geospatial data sets. We also share the lessons learnt from the novel structure for online training.

An analysis of the relationship of land surface temperature with modified normalized difference water index and normalized difference built-up index in Hyderabad City, India

Subhanil Guha, Himanshu Govil — Fri, 21 Mar 2025 00:00:00 +0000

The study analyses the respective relationships between two independent variables, namely, modified normalized difference water index (MNDWI) and normalized difference built-up index (NDBI), and the dependent variable, land surface temperature (LST) in Hyderabad City, southern India. The study used Landsat data applicable to the dry winter season and Pearson's linear correlation coefficient for the correlation analyses. Results show that the LST values for the respective images are also positively correlated. The study also finds that LST shows a moderate negative relationship with MNDWI (average r = -0.57) and a moderate positive relationship with NDBI (average r =0.55). Because the dry winter season affects urban land surface materials in a particular way, built-up areas tend to enhance LSTs in winter, while in this same season, water surfaces tend to reduce LSTs. The study could contribute significantly to sustainable urban landscape planning.

Work Integrated Learning (WIL) Employer Survey in the Geomatics Programme at the Durban University of Technology

Avidesh Raghubar, Dhiren Allopi — Fri, 21 Mar 2025 00:00:00 +0000

The Durban University of Technology (DUT) phased out the National Diploma: Surveying and the B-Tech: Surveying qualifications and introduced a new qualification, Bachelor of the Built Environment (BBE): Geomatics in January 2018. Work integrated learning (WIL) has been recognised as an integral part of the teaching and learning pedagogy within the surveying profession at a national diploma level across many of the technikons and universities of technology (UoTs) nationally, where it has become widely acknowledged as the cornerstone of student development. WIL has now been excluded from the new BBE: Geomatics qualification, which seeks to be more academically oriented. The lack of Workplace learning (WPL) could possibly result in a graduate who exhibits deficiencies in practical knowledge and work-related proficiencies when compared to the traditional technician/technologist that industry has become accustomed to.

The aim of this study was therefore to evaluate the relevance of WIL in the Geomatics programme through interactions with Surveying and Geomatics practitioners in the KwaZulu-Natal (KZN) region, to increase our understanding of industry’s perspectives on WIL, and in so doing, to assist in terms of informed decision-making and best practices. Data were collected through interactions with industry practitioners within the Surveying and Geomatics fraternity. The study was conducted by employing a mixed-methods approach incorporating quantitative and qualitative methods. The quantitative method was, however, the predominant technique since it constituted a significant part of the study. The qualitative method involved analysis of employer comments from the open-ended questions on the questionnaire survey. The findings confirmed that there is significant consensus from industry regarding the importance and relevance of WIL in promoting an enriching career-focused education, and in facilitating the acquisition of discipline knowledge, practical proficiency, graduate attributes, employability skills, and core competencies that will culminate in an all-round holistically thinking graduate to meet the needs of industry and to sustain a knowledgeable, modern, and skilled workforce for the built environment.