GISLAB c/o DICAM -ICAR CNR - Italy University of PalermoExploring 3D models forgeospatial data management: an application of TEN model Andrea Scianna firstname.lastname@example.org GISLAB - http://gislab.geomatica.unipa.it/ University of Cagliari (Italy) 10-12 May 2012
Introduction - surface and volume based modelsUsually, in GIS, the model used to describeobjects is a surface model.Some recent GIS software today allows add forsome element a volume based description (suchas voxels).
Introduction: GIS features GIS is a system whose hardware and software allow for storage, retrieval, mapping, and analysis of geographic data. A GIS database should also characterized by "topology“ properties by which to define the spatial relationships between features.But, today, GIS are often based on other issuessuch as interoperability and cooperativemanagement of geographic data with dynamicmulti-dimensional and distributed GIS -Management source by Web-GIS software.
CNR-Unipa GISLab goalsAt GISLAB (CNR - University of Palermo) theresearch activities on 3D started, in 2004 year,studying conceptual models for therepresentations of 3D urban environment.It has been explored, the possibility to structureand manage 3D objects through primitivescompliant to GML3 language also adding topologyand attributes.The final result of these studies was theproposition of GIANT (Geographic InteroperableAdvanced Numerical Topological 3 Dimensional)model
GIANT modelBased on GIANT model, many tools has beenrealized at GISLAB, initially as stand aloneapplications, to build and browse 3D models,demonstrating the capability to realize andmanage full 3D GIS of urban environment.
New GISLab goalsIn order to support the use of the 3D modeland develop it better to be more powerful it isnecessary to build of instruments for: generating 3D models, of different environment users are interested to; saving 3D models on geospatial database browsing of 3D models by webservices, with internet browsers
Structure of the system WFS 3D basedWith a PRIN 2007 Italian research project «Interoperabilityand cooperative management of geographic, dynamic,multidimensional and distributed data with Free and OpenSource GIS» a system capable to deploy a 3D WebFeature Service has been developed, in order to allow theaccess to 3D cartograhy and browse it through webbrowsers.See WebSite http://gislab.geomatica.unipa.it Blender 3D model
WEB Browsing to GIANT model Query Interface for browsing 3D models (GIANT compliant) by geospatial web services and internet browsers has been realized.
Browsing 3D models (GIANT compliant) bygeospatial web services and internet browsers Browser
Exploring new modelsSuitable models forplanning could besurface element models,while a volume basedmodel could be moresuitable for terraindescription in order tocarry out terrainanalyses, but volumebased models could beused to derive surfacemodels
About 3D modelsActually, two ways could exist in order to obtain aglobal model: a first one in which the model is composed by surface and volume object; this mixed model could anyway results too complex to manage; a second one in which the model is composed only by surface objects which could be derived from the boundary of a TEN model or part of it (e.g. for terrain blocks); so the objects for which could be required a triangular discretization, to perform whatever possible calculations, might be easily converted from surface to volume model and vice versa.
State of the artThe models are generally designed to meet twomain requirements, i.e. the support of the 3Dtopology and 3D visualization in real time.
TEN model On these bases, for the last experimentation, a tetrahedral model has been chosen because of well- suited to perform processing related to the global behavior of some real world elements such as the soil.A TEN is a homogeneous simplicial complex ofdimension 3 consisting of simplexes ofdimension 3 connected by faces. air building road soil ground tunnel
The TENThe definition of TEN implies several important features:• there are no self-intersections in the TEN• there are no isolated edge or faces in the TEN (becauseit is homogeneous in size)• there aren’t isolated tetrahedra in the TEN (since thesewould not be linked through the tetrahedra faces)In addition to the requirements of this definition, TENmodel, considered in this paper, consists of positivelyoriented simplexes of dimension 3. As a result, twoneighboring tetrahedra share a triangle from a geometricalpoint of view, but due to the positive orientation of bothsimplexes of dimension 3, the boundary triangles of thetetrahedra have the same geometry but oppositeorientation.
TEN useBesides the use of TEN models is veryuseful when it is necessary to performcalculation that require a volume elementbased model, such as finite element; afterprocessing that surface result of calculationmay be converted back to surface elementmodel.
Spatial modellingSpatial data modeling is the process todescribe spatial objects in the real world sothey can be represented in a form that can beeasily understood and used.In a volume based approach, parts of realworld are considered volume partitions: a setof volumes, that do not overlap, that shapethe space of closed form (ie no gaps in thedomain).
Spatial modellingThe description of real world presented here isbased on a full 3D triangular approach, for itsbenefits in maintaining data consistency,robustness and modifiability.
Experimenting on volumetric featuresAlthough the physical world is made up ofvolumetric features, some surface features couldstill be very useful, because they mark theborder between two volumetric features. In ourmodel, in this step of experimentation, surfacefeatures may exist, but only as derived feature.This also applies to the line and point features.
Spatial modellingThe tetrahedral network consists of tetrahedra,triangles, edges and nodes. These simplexes are builtrecursively: a tetrahedron is defined by four triangles,a triangle from three edges and an edge with twonodes.The simplicial homology offers a mathematicaldescription of the simplexes and their mutualrelationships. A very important feature in themanagement of the geometries is the orientation, as itis the basis for determining the basic relationshipssuch as left/right and internal/external; simplicialhomology allows full control over the orientation ofsimplexes in each dimension.
Spatial modellingAnother important aspect of this approach is therepresentation of features by several tetrahedra. Inmathematical terms this is known as simplicialcomplex. Since the volume is almost alwaysrepresented by more than a tetrahedron, simplicialcomplex operations are necessary for developmentof model here described.
From Surfaces to TEN and vice-versaActually this experiment and hence the modelare used to understand how a model based onobjects described as surface elements mayinclude objects whose surface descriptioncomes from a TEN description. This means thatwhatever part of the surface model, that comesfrom a volumetric description like TEN, isprocessed, the transformation process fromsurface description to volume elements(discretization) is posssible in bi-directional way
Transferring Surface andSurfaces Volume based 3D models in a PostgreSQL+ Blender PostGIS geospatial DB Python Visualization PostgreSQL+Volumes PostGIS 3D Modellation TetGen Simplex Paraview Geo
Browsing the model in ParaviewGeoSteps that lead to the display of the 3D model objects modelling with a CAD and exporting in a format supported by TetGen, objects creation with the tetrahedronisation software TetGen; importing of files into the software developed to populate the database for PostgreSQL; exporting of database tables in VTK format to view the model in ParaviewGeo
Applications usedIn order to carry out our experimentation many softwarehave been used: objects modelling has been performed using CAD software; software TetGen has been used for objects creation with the tetrahedronisation; Expressly developed software for importing of files to populate PostgreSQL database; exporting of database tables in VTK format to view the model in ParaviewGeo
Archiving tetrahedrons in PostgreSQL tablesIn order to populate the tables in the PostgreSQLRDBMS with results of tetrahedronisation made bythe TetGen, an application has been written. Bythis application it is possible to exports the data inthe format *.VTK for viewing.
Conclusiona full-volume approach not only helps to improvethe analytical skills, but also allows futureintegration of topographic data with other 3Ddata. Although the price of this approach interms of storage space is large.
ConclusionIt is possible to derive a surface model from atetrahedral volume based model and –viceversa;But it also possible to write the two model(surface based model as seen of volume basedmodel and volume based model in order toperform all possible calculation working bothwith surface model and volume based model).
GISLAB c/o DICAM -ICAR CNR - Italy University of PalermoThank you for your attention !
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