Abstract
This paper proposes a generic workflow for using Unmanned Aerial Vehicles (UAV) to produce acceptable cadastral plans in Ghana. This was done by firstly verifying in the field UAV restricted zones specified by the Ghana Civil Aviation Authority (GCAA) and subsequently analyzing ground and aerial survey data from two sites within the Tema Municipality. The data analyzed consisted of one set of boundary coordinate data of the sites obtained from a static Global Navigation Satellite System (GNSS) survey and another set from on-screen digitization of site boundaries from aerials obtained from a Mavic Air UAV weighing 430 g with a camera resolution of 12 megapixels flying at altitudes of 40 and 60 m. A comparison of the two sets of boundary coordinates data showed differences under the limit of +/-3 ft specified by the Survey and Mapping Division (SMD) of the Lands Commission of Ghana. The paper thus outlines a generic workflow as follows: (1) Determining if selected site is within a flight restricted zone (2) Undertaking field reconnaissance to determine appropriate flight parameters and ground control point locations (3) Processing UAV imagery to obtain orthomosaics (4) Performing on-screen digitizing of site boundaries from orthomosaics and (5) Obtaining accurate boundary turning point coordinates from digitized boundary. The paper concludes that this approach if accepted may be used in obtaining multiple cadastral plans within built up areas from a single UAV flight and recommends that UAV and ground control data be submitted in Geotiff and Rinex formats respectively to facilitate checks by the Examinations Unit of the SMD. Keywords: unmanned aerial vehicles, cadastral plans, ground control points, global navigation satellite system, orthomosaic DOI: 10.7176/JEES/11-2-04 Publication date: February 28 th 2021
Highlights
The Survey Act of 1962 of Ghana, Act 127 defines cadastral plans as plans purporting to show boundaries of land with accuracy and giving exact measurements by which the boundaries may be demarcated on the ground such maps or plans being made in conformity with the result of a survey carried out by an Official Surveyor or Licensed Surveyor to be certified by him and requiring whether made by an official surveyor or by a licensed surveyor to be approved by the Chief Survey Officer or any person appointed for that purpose (Fosu and Derby 2008).Currently the predominant technique used for cadastral surveys in Ghana is either by static Global Navigation Satellite Systems (GNSS) or Total Station methods or a combination of both
The paper outlines a generic workflow that can be used to surveyors in Ghana to produce cadastral plans to meet accuracy specifications stipulated by the Survey and Mapping Division (SMD) of Ghana
A major advantage of the approach suggested in this paper is that with one flight and the resulting orthomosaic which has been georeferenced using ground control points surveyed by appropriate GNSS methods and checked by SMD, several boundaries can be digitized to meet cadastral accuracy specifications especially in developed and built-up areas
Summary
The Survey Act of 1962 of Ghana , Act 127 defines cadastral plans as plans purporting to show boundaries of land with accuracy and giving exact measurements by which the boundaries may be demarcated on the ground such maps or plans being made in conformity with the result of a survey carried out by an Official Surveyor or Licensed Surveyor to be certified by him and requiring whether made by an official surveyor or by a licensed surveyor to be approved by the Chief Survey Officer or any person appointed for that purpose (Fosu and Derby 2008).Currently the predominant technique used for cadastral surveys in Ghana is either by static Global Navigation Satellite Systems (GNSS) or Total Station methods or a combination of both. Mantey and Tagoe, (2019) have demonstrated that unmanned aerial vehicle (UAV) technology and data may be suitable for performing cadastral work in Ghana. In other jurisdictions UAV technology and data has been found to be suitable for achieving desired positional accuracy for cadastral work in Manyoky et al (2011) in Switzerland, Zrinjski et al (2019) in the Republic of Croatia, Yuwono et al (2018) and Ramadhani (2016) in Indonesia, Mumbone (2015) in Namibia and Volkman and Barnes (2014) in Albania. The main aim of this paper is to propose a generic workflow that can be used for cadastral surveys using unmanned aerial vehicles while maintaining the accuracy requirements stipulated by the Survey and Mapping Division (SMD) of the Lands Commission of Ghana. Site 1 with a size of approximately 0.455 acres is bounded by latitudes 005°39'19.37"N and 005°39'21.29"N and longitudes 000°01'39.55"W and 000°01'38.57"W while site 2 approximately 0.152 acres lies between latitudes 005°38'24.24"N and 005°38'25.45"N and longitudes 000°01'21.15"W and 000°01'20.52"W
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