The Potential of Active Contour Models in Extracting Road Edges from Mobile Laser Scanning Data

Active contour models present a robust segmentation approach, which makes efficient use of specific information about objects in the input data rather than processing all of the data. They have been widely-used in many applications, including image segmentation, object boundary localisation, motion tracking, shape modelling, stereo matching and object reconstruction. In this paper, we investigate the potential of active contour models in extracting road edges from Mobile Laser Scanning (MLS) data. The categorisation of active contours based on their mathematical representation and implementation is discussed in detail. We discuss an integrated version in which active contour models are combined to overcome their limitations. We review various active contour-based methodologies, which have been developed to extract road features from LiDAR and digital imaging datasets. We present a case study in which an integrated version of active contour models is applied to extract road edges from MLS dataset. An accurate extraction of left and right edges from the tested road section validates the use of active contour models. The present study provides valuable insight into the potential of active contours for extracting roads from 3D LiDAR point cloud data

Accuracy Checks in the Production of Orthophotos

Orthophotos have been used extensively in many applications today. In an attempt to map the earth’s surface in a shortest possible time and provide information for monitoring and planning, Orthophotos have proved reliable as far as these are concerned. Orthophotos are one of the most important base layers of data for GIS systems. The use of Orthophotos in a GIS often implies seamless image data. The major advantage of Orthophotos is their ability to be produced in a short time to provide up-to-date information for urgent planning. They are also produced at a less expensive production price than line or vector maps. The need therefore for quick and reliable data for many rising applications has led to the development in this technology and hence finding ways to make it better in terms of its appearance (radiometric enhancements) and geometric accuracy.This paper looks at the creation of an Orthophoto and enumerates the factors that ensure the geometric accuracy of the Orthophoto. Users of Orthophotos must understand that to make measurements on an Orthophoto, oneneeds to know the quality of the underlying surface description since this affects the geometric accuracy of the Orthophoto. In this paperthe geometric accuracy  with which an orthophoto is produced is analysed.Accuracies during theorientation of the input image and scanning resolution of the scanned image and accuracy at DTMsstage are considered in this paper. Keywords: Orthophoto, geometric accuracy, orientation and DTM

Between the tides: modelling the elevation of Australia’s exposed intertidal zone at continental scale

The intertidal zone represents a critical transition between marine and terrestrial ecosystems, supporting a complex mosaic of highly productive and biologically diverse habitats. However, our understanding of these important coastal environments is limited by a lack of spatially consistent topographic data, which can be extremely challenging and costly to obtain at continental-scale. Satellite remote sensing represents an important resource for monitoring extensive coastal zones. Previous approaches to modelling the elevation of the intertidal zone using earth observation (EO) data have been restricted to small study regions or have relied on manual image interpretation, thus limiting their ability to be applied consistently over large geographic extents. In this study, we present an automated open-source approach to generate satellite-derived elevation data for over 15,387 km2 of intertidal terrain across the entire Australian coastline. Our approach combines global tidal modelling with a 30-year time series archive of spatially and spectrally calibrated Landsat satellite data managed within the Digital Earth Australia (DEA) platform. The resulting National Intertidal Digital Elevation Model (NIDEM) dataset provides an unprecedented three-dimensional representation of Australia's vast exposed intertidal zone at 25 m spatial resolution. We validate our model against LiDAR, RTK GPS and multibeam bathymetry datasets, finding that modelled elevations are highly accurate across sandy beach (±0.41 m RMSE) and tidal flat environments (±0.39 m RMSE). Model performance was least accurate (±2.98 m RMSE) within rocky shores and reefs and other complex coastal environments with extreme and variable tidal regimes. We discuss key challenges associated with modelling intertidal elevation including tidal model performance and biased observations from sun-synchronous satellites, and suggest future directions to improve the accuracy and utility of continental-scale intertidal elevation modelling. Our model can be applied to tidally-influenced coastal environments globally, addressing a key gap between the availability of sub-tidal bathymetry and terrestrial elevation data

Assessing the influence of DEM source on derived streamline and catchment boundary accuracy

Accurate DEM-derived streamlines and catchment boundaries are essential for hydrological modelling. Due to the popularity of hydrological parameters derived mainly from free DEMs, it is essential to investigate the accuracy of these parameters. This study compared the spatial accuracy of streamlines and catchment boundaries derived from available digital elevation models in South Africa. Two versions of Stellenbosch University DEMs (SUDEM5 and DEMSA2), the second version of the 30 m advanced spaceborne thermal emission and reflection radiometer global digital elevation model (ASTER GDEM2), the 30 and 90 m shuttle radar topography mission (SRTM30 and SRTM90 DEM), and the 90 m Water Research Commission DEM (WRC DEM) were considered. As a reference, a 1 m GEOEYE DEM was generated from GeoEye stereo images. Catchment boundaries and streamlines were extracted from the DEMs using the Arc Hydro module. A reference catchment boundary was generated from the GEOEYE DEM and verified during field visits. Reference streamlines were digitised at a scale of 1:10 000 from the 1 m orthorectified GeoEye images. Visual inspection, as well as quantitative measures such as correctness index, mean absolute error, root mean squares error and figure of merit index were used to validate the results. The study affirmed that high resolution (<30 m) DEMs produce more accurate parameters and that DEM source and resampling techniques also play a role. However, if high resolution DEMs are not available, the 30 m SRTM DEM is recommended as its vertical accuracy was relatively high and the quality of the streamlines and catchment boundary was good. In addition, it was found that the novel Euclidean distancebased MAE and RMSE proposed in this study to compare reference and DEM-extracted raster datasets of different resolutions is a more reliable indicator of geometrical accuracy than the correctness and figure of merit indices.Keywords: hydrology, catchment delineation, digital elevation model, correctness index, figure of merit index, Euclidean distance inde

Simulating Environmental Impacts Based On The Example Of Roşia Montană

One of the challenges of modern terrain modelling methods is to incorporate non-existing, planned features in the output. Remote sensing based solutions can only detect structures and shapes that are already present in the environment. In order to assess the impacts of a planned development on the surrounding landscape properly it is inevitable to solve this issue. In addition to the environmental, social and economic consequences, mining activities, especially open cast mining will also leave significant scars on the landscape. These can not only have a visual effect but also impact local weather conditions by changing winds, precipitation patterns. The current paper demonstrates a collection of methods and techniques able to cope with the various challenges that arise when modelling the landscape impacts of such developments. The experiments were performed in the area of Roşia Montană, where a Canadian company plans to create the largest open cast gold mine in Europe. The results of the terrain modelling process allow for the quantification of the estimated impacts on the terrain and the land cover of the area caused by the mining project. The presented methodology and visualisation tools can also facilitate the decision support mechanisms making the communication ‘more understandable’ amongst stakeholders; information meetings and public hearings involving organizing groups at any level. Obtaining the results required the development of several unconventional techniques especially in terrain modelling and visual landscape simulation, involving the combination of sometimes very different base methods

Trends and concerns in digital cartography

CISRG discussion paper ;

Directory of research and development based on Ordnance Survey small scales digital data

Special issue (CISRG - Cartographic Information Systems Research Group) ;

Enhanced mapping of artificially modified ground in urban areas : using borehole, map and remotely sensed data

The report described here is focused on how using boreholes and attributes from boreholes increased and enhanced the mapping of Artificially Modified Ground, and helped measure landscape evolution change in the urban environment. These attributes from boreholes include the presence of AMG in a borehole, the thickness of AMG recorded, the start height of a borehole and the location of boreholes (and other boreholes in close proximity) with modern topological features and geological maps