Andrea Scianna and Rosanna Sciortino on "Exploring 3D models for geospatial data management: an application of TEN model"

1. GISLAB c/o DICAM -
ICAR CNR - Italy University of Palermo
Exploring 3D models for
geospatial data management:
an application of TEN model
Andrea Scianna
andrea.scianna@cnr.it
GISLAB - http://gislab.geomatica.unipa.it/
University of Cagliari (Italy) 10-12 May 2012

2. Introduction - surface and volume
based models
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).

3. 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 issues
such as interoperability and cooperative
management of geographic data with dynamic
multi-dimensional and distributed GIS -
Management source by Web-GIS software.

4. 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

5. GIANT 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.

6. New GISLab goals
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

7. Structure of the system WFS 3D based
With 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

8. WEB Browsing to GIANT model
Query
Interface for browsing 3D models (GIANT
compliant) by geospatial web services and
internet browsers has been realized.

9. Browsing 3D models (GIANT compliant) by
geospatial web services and internet browsers
Browser

10. Exploring new models
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

11. About 3D models
Actually, two ways could exist in order to obtain a
global 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.

12. 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.

13. 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 of
dimension 3 consisting of simplexes of
dimension 3 connected by faces.
air building
road
soil
ground
tunnel

14. The TEN
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.

15. TEN use
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.

16. Spatial modelling
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).

17. 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.

18. Experimenting on volumetric features
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.

19. Spatial modelling
The tetrahedral network consists of tetrahedra,
triangles, edges and nodes. These simplexes are built
recursively: a tetrahedron is defined by four triangles,
a triangle from three edges and an edge with two
nodes.
The simplicial homology offers a mathematical
description of the simplexes and their mutual
relationships. A very important feature in the
management of the geometries is the orientation, as it
is the basis for determining the basic relationships
such as left/right and internal/external; simplicial
homology allows full control over the orientation of
simplexes in each dimension.

20. 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.

21. From Surfaces to TEN and vice-versa
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

22. Transferring Surface and
Surfaces
Volume based 3D models in
a PostgreSQL+
Blender PostGIS geospatial DB
Python
Visualization
PostgreSQL+
Volumes PostGIS
3D Modellation
TetGen Simplex
Paraview Geo

23. Example of Relational schema

24. Browsing the model in ParaviewGeo
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

25. Applications used
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

26. Archiving tetrahedrons in PostgreSQL tables
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.

27. Conclusion
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.

28. 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).

29. GISLAB c/o DICAM -
ICAR CNR - Italy University of Palermo
Thank you for your attention !