GISLAB c/o DICAM -

University of PalermoICAR CNR - Italy

Exploring 3D models for

geospatial data management:

Andrea Sciannaandrea.scianna@cnr.it

GISLAB - http://gislab.geomatica.unipa.it/

an application of TEN model

University of Cagliari (Italy) 10-12 May 2012

� Usually, in GIS, the model used to describe

objects is a surface model.

� Some recent GIS software today allows add for

some element a volume based description (such

as voxels).

Introduction - surface and volume

based models

� 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 issues

such as interoperability and cooperative

management of geographic data with dynamic

multi-dimensional and distributed GIS -

Management source by Web-GIS software.

�

Introduction: GIS features

CNR-Unipa GISLab goals

� At GISLAB (CNR - University of Palermo) the

research activities on 3D started, in 2004 year,

studying conceptual models for the

representations of 3D urban environment.

� It has been explored, the possibility to structure

and manage 3D objects through primitives

compliant to GML3 language also adding topology

and attributes.

� The final result of these studies was the

proposition of GIANT (Geographic Interoperable

Advanced Numerical Topological 3 Dimensional)

model

� Based on GIANT model, many tools has been

realized at GISLAB, initially as stand alone

applications, to build and browse 3D models,

demonstrating the capability to realize and

manage full 3D GIS of urban environment.

GIANT model

In order to support the use of the 3D model

and develop it better to be more powerful it is

necessary 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

New GISLab goals

Structure of the system WFS 3D basedWith a PRIN 2007 Italian research project «Interoperability

and cooperative management of geographic, dynamic,

multidimensional and distributed data with Free and Open

Source GIS» a system capable to deploy a 3D Web

Feature Service has been developed, in order to allow the

access to 3D cartograhy and browse it through web

browsers.

See WebSite http://gislab.geomatica.unipa.it

Blender 3D

model

WEB Browsing to GIANT model

� Interface for browsing 3D models (GIANT

compliant) by geospatial web services and

internet browsers has been realized.

Query

Browsing 3D models (GIANT compliant) by

geospatial web services and internet browsers

Browser

� Suitable models for

planning could be

surface element models,

while a volume based

model could be more

suitable for terrain

description in order to

carry out terrain

analyses, but volume

based models could be

used to derive surface

models

Exploring new models

Actually, two ways could exist in order to obtain a global model:

� a first one in which the model is composed bysurface and volume object; this mixed model couldanyway results too complex to manage;

� a second one in which the model is composed onlyby surface objects which could be derived from theboundary of a TEN model or part of it (e.g. for terrainblocks); so the objects for which could be required atriangular discretization, to perform whateverpossible calculations, might be easily convertedfrom surface to volume model and vice versa.

�

About 3D models

State of the art

� The models are generally designed to meet two

main requirements, i.e. the support of the 3D

topology and 3D visualization in real time.

road

air

soil

ground

building

tunnel

� 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.

TEN model

A TEN is a homogeneous simplicial complex of

dimension 3 consisting of simplexes of

dimension 3 connected by faces.

� The 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 (because

it is homogeneous in size)

� • there aren’t isolated tetrahedra in the TEN (since these

would not be linked through the tetrahedra faces)

� In addition to the requirements of this definition, TEN

model, considered in this paper, consists of positively

oriented simplexes of dimension 3. As a result, two

neighboring tetrahedra share a triangle from a geometrical

point of view, but due to the positive orientation of both

simplexes of dimension 3, the boundary triangles of the

tetrahedra have the same geometry but opposite

orientation.

The TEN

� Besides the use of TEN models is very

useful when it is necessary to perform

calculation that require a volume element

based model, such as finite element; after

processing that surface result of calculation

may be converted back to surface element

model.

TEN use

� Spatial data modeling is the process to

describe spatial objects in the real world so

they can be represented in a form that can be

easily understood and used.

� In a volume based approach, parts of real

world are considered volume partitions: a set

of volumes, that do not overlap, that shape

the space of closed form (ie no gaps in the

domain).

Spatial modelling

� The description of real world presented here is

based on a full 3D triangular approach, for its

benefits in maintaining data consistency,

robustness and modifiability.

Spatial modelling

� Although the physical world is made up of

volumetric features, some surface features could

still be very useful, because they mark the

border between two volumetric features. In our

model, in this step of experimentation, surface

features may exist, but only as 'derived feature'.

This also applies to the line and point features.

Experimenting on volumetric features

� The 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 modelling

� Another important aspect of this approach is the

representation of features by several tetrahedra. In

mathematical terms this is known as simplicial

complex. Since the volume is almost always

represented by more than a tetrahedron, simplicial

complex operations are necessary for development

of model here described.

Spatial modelling

� Actually this experiment and hence the model

are used to understand how a model based on

objects described as surface elements may

include objects whose surface description

comes from a TEN description. This means that

whatever part of the surface model, that comes

from a volumetric description like TEN, is

processed, the transformation process from

surface description to volume elements

(discretization) is posssible in bi-directional way

From Surfaces to TEN and vice-versa

Blender

PostgreSQL+

PostGIS

Visualization

Simplex

3D Modellation

Paraview Geo

Python

TetGen

Surfaces

Volumes

Transferring Surface and

Volume based 3D models in

a PostgreSQL+

PostGIS geospatial DB

Example of Relational schema

Steps 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

Browsing the model in ParaviewGeo

In order to carry out our experimentation many software

have 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

Applications used

� In order to populate the tables in the PostgreSQL

RDBMS with results of tetrahedronisation made by

the TetGen, an application has been written. By

this application it is possible to exports the data in

the format *.VTK for viewing.

Archiving tetrahedrons in PostgreSQL tables

� a full-volume approach not only helps to improve

the analytical skills, but also allows future

integration of topographic data with other 3D

data. Although the price of this approach in

terms of storage space is large.

Conclusion

� It is possible to derive a surface model from a

tetrahedral volume based model and –

viceversa;

� But it also possible to write the two model

(surface based model as seen of volume based

model and volume based model in order to

perform all possible calculation working both

with surface model and volume based model).

Conclusion

GISLAB c/o DICAM -

University of PalermoICAR CNR - Italy

Thank you for your attention !