PROCESSING LIDAR INFORMATION PUBLISHEDA. ŞMULEAC*, C. POPESCU*, Laura ŞMULEAC*, Carmen Aurelia PEPTAN**
Abstract: The purpose of this paper is to create a 3D land model based on LIDAR (Light Detection and Ranging) satellite images. LIDAR is an active remote-sensing method based on distance scanning and measurement that produces a DTM (Digital Terrain Model). It “sees through trees” and provides an exact model of the land surface in areas that have been inaccessible so far. LIDAR technology operates in a similar manner as RADAR, which uses radio waves, while LIDAR uses light waves generated by a pulse laser (laser-generated electromagnetic energy is spread by air gas molecules and particulate matter). In general, the wavelengths used by a LIDAR system depend on the type of measurement and vary between 355-1064 nm in the UV – VIS – IR range. Due to the laser beam, LIDAR is small enough to penetrate tree branches and reach the land surface, generating data with an accuracy of up to 1.5 m. While overflying the designated area, a laser beam scans the land and the ground objects. After soil contact, the laser beam returns to the plane and produces both point data and infrared images. Following data collection, the data are processed into a point-derived image. Each 3D point can be visualised in any direction, providing a 3D model of an area. In this way, a segment can be viewed vertically or laterally or it can spin in different directions. All data obtained in this way can be processed in several weeks, unlike manual photogrammetry methods that require months to be finalised. Data processing with the help of LIDAR satellite images facilitates creating 3D models, detecting and removing points outside the area of interest, modelling the soil surface and filtering data, generating elevation profiles, creating DSM and DTM in raster format, TIN, level curves or slope patterns, classifying soil surface and buildings, vectorisation of buildings, classifying the vegetation (high, medium and low) and detecting and classifying towers and high voltage cables. To create our 3D model, we performed field measurements with the GPS Leica 1200 equipment. For the areas where the GPS measurements could not be taken, we employed the Leica TC805 Total Station. To generate a 3D model of the terrain based on LIDAR images, we used Global Mapper v 16.1. Our source was the second, improved version of the ASTER GDEM altimetry data set, which was released by NASA and METI. GDEM2 has 260,000 more stereo pair images than GDEM1. Global Mapper is a viewing instrument that can display the most common raster, elevation or vector data sets. For viewing, we used the "ASTER GDEM v2 Worldwide Elevation Data (1 arc-second resolution) data set and SRTM (3 arc-second Resolution) data.
Key words: LIDAR, 3D Model, GPS, ASTER, SRTM, DTM, Global Mapper, TransDatRO, WGS 1984