Updating the Coordinates of Old Land Certificates to the National Geodetic Network of Cameroon: The Case of Foumban in The Noun Division of the West Region of Cameroon

ABSTRACT

Coordinate transformation is one of the commonest activities in geodesy and other geospatial disciplines. Transformation of coordinates facilitates the integration of geodetic coordinates of points obtained from different sources onto a common geodetic reference datum. This can be achieved both by field observations and mathematically using the different transformation models proposed by scientists. It can be achieved by carrying out field work using the GNSS instrument or total station making use of known reference points to perform surveys through triangulation or trilateration. To achieve this mathematically requires the determination of transformation parameters between the different geodetic datum. For this study Helmert’s 2-D transformation was used to mathematically transform coordinates from the local to the NGNC coordinate system after calculation of transformation of parameters by the least square method. Findings from the study reveal that for each land to be updated the transformation parameters must be calculated due to the fact that the previous coordinate system does not have defined parameters, that is for each survey, the x and y-axis were assumed

GENERAL INTRODUCTION

BACKGROUND OF THE STUDY

A fundamental activity in land surveying is the integration of multiple sets of geodetic data, gathered in various ways, into a single consistent data set, that is into a common geodetic reference frame. In the past it was sufficient to combine all such data using a locally, mostly arbitrarily, defined geodetic datum (Featherstone, 1996; Yang, 2009). In recent years, a growing trend toward the use of satellite positioning and global mapping satellite systems has been developed providing position – based products in a world reference frame (Featherstone, 1996; Yang, 2009). One of the principal purposes of such a world frame is to eliminate the use of multiple geodetic datum. But, until such a world geodetic reference frame is accepted, used and implemented worldwide, the satellite data may lead to several practical difficulties when the results need, also, to be related to a geodetic datum, as it is often the case. Such problems arise in several instances, such as navigation, revision of older maps, cadastral surveying, industrial surveying, deformation studies and geo-exploration amongst others (Featherstone, 1996; Yang, 2009). In general, the necessity of transforming data from one reference frame to another is solved by applying a coordinate transformation. Although coordinate transformations are straightforward mathematically, they may cause several problems when applied for various reasons, such as poor knowledge of the distortions and inconsistencies of the local datum, or even lack of sufficient knowledge of geodesy of people who use such transformations. To properly understand coordinate transformations in geodesy, it is essential to understand the relationship between a geodetic reference system, which is mathematically established, and its realization, via geodetic observations, the Geodetic Reference Frame (GRF). Naturally, the GRF has some degree of uncertainty, due to observational errors in the determination of the coordinates of the ground points. Often, there are two GRFs realizing two different systems (local or global), with a number of common network points (Featherstone, 1996; Yang, 2009). Since the GRFs are not perfect realisations of their systems, only a best estimate of the transformation parameters with their respective standard deviations may be computed. In practice, this means that no exact transformation exists between two geodetic coordinate systems.

Positional information about natural and man-made features is shown on maps as coordinates. Hence, coordinates have become an indispensable representative means for accurately mapping out natural resources (Featherstone, 1996). For example, the geologist needs coordinate to carry out geological mapping, while the drilling engineer require the position to be drilled as well as the azimuth the drilling should be done. In view of the foregoing discussion, it is clear that accurate positional information should be provided for proper planning, management and decision making. In view of the above, Global Navigation Satellite Systems (GNSS), particularly, Global Positioning System (GPS) have been widely adopted in geospatial sciences and its related Earth Science disciplines for geodetic purposes. Since its arrival, GPS has become an essential technology that has revolutionized data collection and surveying practices at large. However, for the GPS data to be used locally so that compatibility could be created between maps and other geospatial data produced in the national datum, there is a need to perform coordinate transformation (Featherstone, 1996; Yang, 2009). In doing this, Earth Scientist can comfortably apply the GPS measurement locally with minimal degree of errors that are usually created due to different datum size, shape and origin between the national data (non-geocentric) of countries and the global datum (geocentric) of the GPS.

STATEMENT OF THE PROBLEM