![]() ![]() versus Vector Topology - points, centroids, lines, boundaries - in topology centroid and boundary form an area - single boundaries for adjacent areas Advantage: - less maintenance, high quality Disadvantage: - slower computations Switzerland Original Pruned each boundary is a single line, divided by two polygons (UTM32N projection) Map generalized with v.clean “prune” algorithm in topological GIS GRASS OGC Simple Features versus Vector Topology. points, lines, polygons - replicated boundaries for adjacent areas Advantage: - faster computations Disadvantage: - extra work for data maintenance - in this example the duplicated boundaries are causing troubles Switzerland slivers Map generalized with Douglas-Peucker algorithm in non-topological GIS gaps (Latitude-longitude) ![]() OGC Simple Features versus Vector Topology Simple Features. Vector data model Vector geometry types Point Centroid Line Boundary Area (boundary + centroid) face (3D area) Geometry is true 3D: x, y, z Line Faces not in all GIS! Node Node Vertex Vertex Segment Segment Segment Node Boundary Vertex Vertex Vertex Vertex Centroid Area Raster data model Raster geometry cell matrix with coordinates resolution: cell width / height (can be in kilometers, meters, degree etc.) y resolution x resolution image processing 3D Voxel data for volumetric data 2D/3D Vector data with topology Multidimensional points data Orthophoto Distances Vector TIN 3D Vector buildings Voxel Spatial Data Types Supported Spatial Data Types 2D Raster data incl. ![]() What's GRASS GIS? Raster and 2D/3D topological vector GIS Voxel support (raster 3D volumes) Vector network analysis support Image processing system Visualization system DBMS integrated (SQL) with dbf, PostgreSQL, MySQL and sqlite drivers In GRASS 6.1 translations of the user interface to 16 languages ongoing Interoperability : supports all relevant raster and vector formats From DXF GRASS GIS Brief Introduction Developed since 1984, always Open Source, since 1999 under GNU GPL Written in C programming language, portable code (multi-OS, 32/64bit) International development team, since 2001 coordinated at ITC-irst GRASS master Web site: GNU/Linux MacOSX MS-Windows iPAQ Code is documented in source code files (doxygen) Sample data Mailing lists in various languages Commercial support GRASS: Geographic Resources Analysis Support System Free Software GIS (“software libero”): GRASS master Web site is in Italy: Portable: Versions for GNU/Linux, MS-Windows, Mac OSX, SUN, etc Programming: Programmer's Manual on Web site (PDF, HTML), generated weekly. GRASS: Geographic Resources Analysis Support System Scope: Learn the use of Free Software GIS PART I: Introduction to GRASS and QGIS PART II: Practical examples Neteler neteler at ITC-irst, Povo (Trento), Italy (Document revised November 2006) The GRASS GIS software GIS Seminar Politecnico di Milano Polo Regionale di Como M. The GRASS GIS software (with QGIS) - GIS Seminar ![]()
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