Ghana Flying Labs' survey of Sawla and Lawra served as a critical part of an initiative to support water supply planning under Ghana's National Water Policy.
December 13th, 2024
A topographical survey of the towns of Sawla and Lawra in Ghana, commissioned by MAPLE Consult and supervised by ECOPSIS, marks a significant step toward improving water access in small towns and rural areas. This survey is a key element of a broader feasibility study exploring public-private partnership (PPP) opportunities in water supply. Aligned with Ghana's revised National Water Policy (2023), the project aims to assess the investments needed to meet the water demands of these communities.
Using advanced drone-based and ground-level data collection techniques, the survey produced high-precision (2cm) georeferenced orthophotos, digital elevation models (DEMs), and shapefiles. Key deliverables included detailed spatial data on infrastructure such as roads, public institutions, water bodies, and water supply facilities like boreholes, reservoirs, and treatment plants. By providing accurate topographical data, the project supports infrastructure planning and development, enabling more effective water resource management and engineering design.
The mapping project aimed to achieve the following deliverables:
Pre-Survey Preparations
Before the commencement of the survey, the SKT Live and Ghana Flying Labs team prepared a flight plan for the aerial survey, subdividing the area into manageable sections. Flight altitudes were adjusted to between 200–250 metres based on terrain and survey objectives. A field reconnaissance was conducted to identify take-off and landing zones, as well as emergency landing spots. Control pillars were also selected to serve as base stations for Post-Processing Kinematic (PPK) data collection.
Aerial Survey Execution
The survey utilised the WingtraOne drone, a PPK-enabled aerial mapping solution, for high-accuracy data acquisition. Separate base stations were established in Sawla and Lawra, ensuring precise georeferencing of the survey data. The collected images and corresponding GPS data from the base stations were downloaded for post-processing.
Data Post-Processing Workflow
1. Image and GPS Data Processing:
Data from the WingtraOne drone and the base stations were processed using WingtraHub software. The base station coordinates were converted to the WGS84 coordinate system to meet software requirements.
2. Photogrammetry:
The processed data, including raw images and base station coordinates, were imported into Agisoft Metashape, enabling the creation of georeferenced orthomosaics and point clouds. The outputs were subsequently exported in the Universal Transverse Mercator (UTM) coordinate system (WGS84 UTM Zone 30N).
3. Feature Digitisation:
Using QGIS and AutoCAD, key features such as buildings, large drainage systems, bridges, and rivers were digitised from the orthomosaics to create detailed topographical maps.
4. Contours and Spot Heights:
The point cloud data was utilised to generate contour maps and spot height datasets. These outputs were particularly critical for road corridor design and other infrastructure projects.
Features digitized from the survey included:
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By leveraging these outputs, the survey provides a robust foundation for infrastructure design, water supply development, and sustainable resource management. This initiative underscores the value of integrating advanced geospatial technologies in addressing critical development challenges.
