Abstract
National Geographic Institute of Spain (IGN-ES) has launched a new production system for automatic river network extraction for the Geospatial Reference Information (GRI) within hydrography theme. The goal is to get an accurate and updated river network, automatically extracted as possible. For this, IGN-ES has full LiDAR coverage for the whole Spanish territory with a density of 0.5 points per square meter. To implement this work, it has been validated the technical feasibility, developed a methodology to automate each production phase: hydrological terrain models generation with 2 meter grid size and river network extraction combining hydrographic criteria (topographic network) and hydrological criteria (flow accumulation river network), and finally the production was launched. The key points of this work has been managing a big data environment, more than 160,000 Lidar data files, the infrastructure to store (up to 40 Tb between results and intermediate files), and process; using local virtualization and the Amazon Web Service (AWS), which allowed to obtain this automatic production within 6 months, it also has been important the software stability (TerraScan-TerraSolid, GlobalMapper-Blue Marble , FME-Safe, ArcGIS-Esri) and finally, the human resources managing. The results of this production has been an accurate automatic river network extraction for the whole country with a significant improvement for the altimetric component of the 3D linear vector. <br><br> This article presents the technical feasibility, the production methodology, the automatic river network extraction production and its advantages over traditional vector extraction systems.
Highlights
During the last 3 years, the National Geographic Institute of Spain (IGN-ES) has been working on the improvement of the production system of the hydrographic reference geoinformation, on the subject of the automatic capture of the stream vector network, which traditionally had been produced by manual methods using photogrammetric restitution techniques
The main challenges for IGN-ES is on one hand the size of the country, with 504.000 km2, and in the other hand, the need of updated high resolution hydrographic geoinformation, keeping the current planimetric resolution, and with significant improvement in the altimetric resolution, according to the possibilities provided by the Lidar data
This improved geoinformation must be produced fully coherent with the altimetric data obtained from the LiDAR data, high resolution tridimensional stream network, hydrological and flow direction digital Elevation Models (DTMs) able to be integrated in hydrological tools for analysis, planning and management, delimitation of physical contours of drainage basins, codification of hydrographic stream network, etc
Summary
After determining the optimum area unit to divide the territory for processing, a number of corrections to the mosaics were built and corrected in several steps, mainly to remove obstacles from transport network and a hydrological calculation was done, based on accumulation, using an average basin size based on the contrast with the existing cartography ( number of river streams and channel heads) The results using this first approach showed that additional large manual editing was needed, and the Z accuracy was good and consistent, planimetric results did not improve the current existing data available in the IGN-ES (national topographic base with accuracy in XY < 5 meters 99% level of confidence). Several test were made in different steps of the works to select the best software and tools to be used in the production chain
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