Abstract
Abstract. The ability to build three-dimensional models through technologies based on satellite navigation systems GNSS and the continuous development of new sensors, as Airborne Laser Scanning Hydrography (ALH), data acquisition methods and 3D multi-resolution representations, have contributed significantly to the digital 3D documentation, mapping, preservation and representation of landscapes and heritage as well as to the growth of research in this fields. However, GNSS systems led to the use of the ellipsoidal height; to transform this height in orthometric is necessary to know a geoid undulation model. The latest and most accurate global geoid undulation model, available worldwide, is EGM2008 which has been publicly released by the U.S. National Geospatial-Intelligence Agency (NGA) EGM Development Team. Therefore, given the availability and accuracy of this geoid model, we can use it in geomatics applications that require the conversion of heights. Using this model, to correct the elevation of a point does not coincide with any node must interpolate elevation information of adjacent nodes. The purpose of this paper is produce a Matlab® geodetic software for processing airborne LIDAR bathymetry data. In particular we want to focus on the point clouds in ASPRS LAS format and convert the ellipsoidal height in orthometric. The algorithm, valid on the whole globe and operative for all UTM zones, allows the conversion of ellipsoidal heights using the EGM2008 model. Of this model we analyse the slopes which occur, in some critical areas, between the nodes of the undulations grid; we will focus our attention on the marine areas verifying the impact that the slopes have in the calculation of the orthometric height and, consequently, in the accuracy of the in the 3-D point clouds. This experiment will be carried out by analysing a LAS APRS file containing topographic and bathymetric data collected with LIDAR systems along the coasts of Oregon and Washington (USA).
Highlights
A direct georeferencing (DG) system provides the ability to directly relate the data collected by a remote sensing system to the Earth, by accurately measuring the geographic position and orientation of the sensor without the use of traditional groundbased measurements (Mostafa et al, 2001; Pepe et al, 2015)
If the coordinate of point clouds are in geographic coordinates, in the software there is an algorithm that allows to transform the by geographic coordinates to plane coordinates, through the well-transform known in the literature Having available a more accurate geoid model, it can be used provided it is in the format East, North, geoid undulation
The software developed in Matlab® allowed to transform the point clouds from ellipsoidal to orthometric height
Summary
A direct georeferencing (DG) system provides the ability to directly relate the data collected by a remote sensing system to the Earth, by accurately measuring the geographic position and orientation of the sensor without the use of traditional groundbased measurements (Mostafa et al, 2001; Pepe et al, 2015). With recent advances in LIDAR (Light Detection And Ranging) technology, coastal managers have the capacity to acquire high resolution digital elevation data covering the littoral or inter-tidal zone This development of hardware has been followed by a development of a new data file format standard known as the American society for Photogrammetry and Remote Sensing (ASPRS) Lidar Exchange Format (LAS) (Samberg, 2007). The second problem is to maintain all the specific information of the LIDAR data; this is useful in applications of airborne laser scanning as in them, working on large areas, the geoid undulation can take considerably variable values in the survey area; transform the point clouds with a height orthometric preserves information about the nature and quality of the point. In the literature there are software solutions (Hug et al, 2004) but who do not are not in the public domain and not allow you to check for errors or implementations as may occur with this algorithm in Matlab®
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