Abstract
ABSTRACTThe georeferencing process is crucial to the accuracy of terrestrial laser scanner (TLS) data, in particular in the context of diachronic studies relying on multi-temporal surveys. The use of Ground Control Points in the georeferencing process can however be complex when confronted with the practical constraints of coastal surveying. A simple and quick alternative method called “pseudo-direct georeferencing” is proposed in the present paper. This method involves internal inclinometers to measure roll and pitch angles and a centimetric GPS to measure the position of the TLS center and the position of one backsight target. When assessing the transformational uncertainty by using a set of independent ground validation points for both classical indirect and proposed pseudo-direct methods, we respectively obtain root mean square errors of 4.4 cm for the indirect method and 3.8 cm for the pseudo-direct method.
Highlights
Coastal landscapes are shaped by a set of forcing factors, highly variable both in time and location, making the littoral zone a very dynamic environment
Because these ground validation points (GVPs) are reflective targets which are not taken into account in the registration process, 14 GVP are available to assess indirect georeferencing, while 27 GVPs are available for pseudo-direct georeferencing
The protocol involves internal inclinometers to measure roll and pitch angles and a Real-Time Kinematic (RTK) GPS to measure the position of the terrestrial laser scanner (TLS) center and the position of one backsight target
Summary
Coastal landscapes are shaped by a set of forcing factors, highly variable both in time and location, making the littoral zone a very dynamic environment. The most basic method for coastal landscape surveying is the GPS or tacheometer pole measurement, a point-wise method associated with low spatial resolution and strong uncertainties. The position of the measured points is expressed in a local coordinate system associated with the sensor, generally referred in literature and further mentioned as Intrinsic Coordinate System (ICS). Georeferencing consists in transforming the registration of the point cloud from the ICS into an absolute or GLobal Coordinate Systems (GLCS), generally associated to a geodetic datum. This transformation is associated with the matrix operator MIGL (Figure 1), a unique combination of a translation and a rotation. A set of six transformation parameters is required for this registration
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