LIDAR (Light Detection and Ranging) is one of the most recent technologies in surveying and mapping. LIDAR is based on the combination of three different data collection tools: a laser scanner mounted on an aircraft, a Global Positioning System (GPS) used in phase differential kinematic modality to provide the sensor position and an Inertial Navigation System (INS) to provide the orientation. The laser sends towards the ground an infrared signal, which is reflected back to the sensor. The time employed by the signal, given the aircraft position and attitude, allows computation of the earth point elevation. In standard conditions, taking into account the flight (speed 200 -250 km / hour, altitude 500 -2,000 m) and sensor characteristics (scan angle ± 10-20 degrees, emission rate 2,000-50,000 pulses per second), earth elevations are collected within a density of one point every 0.5-3 m. The technology allows us therefore to obtain very accurate (5-20 cm) and high resolution Digital Surface Models (DSM). For many applications, the Digital Terrain Model (DTM) is needed: we have to automatically detect and discard from the previous DSM all the features (buildings, trees, etc.) present on the terrain. This paper describes a procedure that has been implemented within GRASS to construct DTMs from LIDAR source data.(DSM), which describes the Earth's surface, including all the objects on the ground and the digital terrain model (DTM) reproducing the "natural" ground surface, i.e. the bare Earth surface. Both surfaces are being widely used in many fields such as topographic mapping, urban planning, ecological and environmental studies, flood prevention and drainage mapping, forestry, landscape design and infrastructure construction, maintenance and management. Moreover, with the development of 3-D GIS, the DEMs assume even more importance, because of the central role played by topographic data within GIS.The conventional techniques used to collect altimetric data include land surveying and aerial photogrammetry. In the past few years, a new method to measure the topography of the Earth's surface has attracted interest because of its high accuracy, low time requirements, and competitive or lower costs than earlier methodologies (Shrestha et al. 2000). This method, known as LIDAR (Light Detection and Ranging) or ALSM (Airborne Laser Swath Mapping) has a very simple measurement principle (Baltsavias 1999, Wehr and Lohr 1999, NOAA-USGS 2002. It is given by the combination of three different types of equipment: a laser scanner, the global navigation system (GPS) and an inertial navigation system (INS). The laser scanner is installed on the aircraft as the phogrammetric camera usually is. Laser pulses are emitted towards ground with high repetition rates per second (2,000 up to 50,000) and are reflected back to the instrument. A mirror inside the laser transmitter rotates in a sweep motion perpendicular to the direction of flight in order to blanket the surface of the Earth in a strip buffering this direction (swath width of up t...
Over the past decade, open source software has become widely accepted across governments, industries and academia. The geospatial domain is no exception and this trend is also reflected in geospatial research and practice. Nowadays, governments and stakeholders from the business sector both participate and promote open geospatial science including open geospatial data and open source geospatial software. As a result, open source geospatial science and software (i.e., open source GIS) is a growing area of research with numerous applications and great potential. The consistent prevalence of open source GIS studies motivated this thematic collection. The contributions are divided into two main categories. In the first, novel open source geospatial software and standards are presented, each of which has been implemented for and applied to a certain use case, and at the same time may be applied to other use cases due to the reproducibility of open source software. The second category presents and discusses the applicability and usability of open source GIS solutions for various interdisciplinary domains, mostly related to urban studies.
Volunteers are the key component in the collection of Volunteered Geographic Information (VGI), so what motivates their participation, what strategies work in recruitment and how sustainability of participation can be achieved are key questions that need to be answered to inform VGI system design and implementation. This chapter reviews studies that have examined these questions and presents the main motivational factors that drive volunteer participation, as determined from empirical research. Some best practices from broader citizen science applications are also presented that may have relevance for VGI initiatives. Finally, a set of case studies from our experiences are used to illustrate how volunteers have been motivated to collect VGI through mapping parties, gamification and working with schools.
Web mapping and the use of geospatial information online have evolved rapidly over the past few decades. Almost everyone in the world uses mapping information, whether or not one realizes it. Almost every mobile phone now has location services and every event and object on the earth has a location. The use of this geospatial location data has expanded rapidly, thanks to the development of the Internet. Huge volumes of geospatial data are available and daily being captured online, and are used in web applications and maps for viewing, analysis, modeling and simulation. This paper reviews the developments of web mapping from the first static online map images to the current highly interactive, multi-sourced web mapping services that have been increasingly moved to cloud computing platforms. The whole environment of web mapping captures the integration and interaction between three components found online, namely, geospatial information, people and functionality. In this paper, the trends and interactions among these components are identified and reviewed in relation to the technology developments. The review then concludes by exploring some of the opportunities and directions. Keywords: web mapping; Web GIS; Internet; online; web services; digital earth; GeoWeb; semantic web; collaborative; development era
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