To address the challenges of sustainable management and development of the
built environment, engineers and facility managers need to exploit the 3D City
models which grown in recent years to include interior space. A crucial issue
for facilitating interaction with these 3D city models is the ability to
integrate 3D BIM into the geospatial context. This requires the use of
specialized software and specific expertise. In order to simplify this process,
we proposed an information system that facilitates the use of BIM for
geo-analysis purposes.
Introduction
BIM4GeoA is a concept for combining existing open source software and open
specification for efficient data management and analysis of Building
Information within its boarder context. The core components are the spatial
database PostgreSQL/PostGIS, the building information server, the industrial
foundation class (IFC), the Google Earth 3D viewer, and the existing 3D OGC
standard (KML, CityGML).
Our work presents the procedure used to enable the development of this new
expert system as applied to the context of 3D Web GIS.
Figure 1 - The IFC parser.A thorough analysis of the strength and
weakness of these different components has been undertaken to employ it is
strength and override its weakness.
The system architecture is operationally used in developing different
applications for the management of a university campus; a large potential is
provided for operational tasks of facility management department, such as
utilities infrastructure, as well as public community (student, staff) like
routing application, searching for a person with defined criteria.
Since the advent of Computer-Aided Design (CAD) and Geographical Information
System (GIS) tools, project participants have been increasingly leveraging
these tools throughout the different phases of a civil infrastructure project.
For example, professionals in urban planning, engineers, utility management are
especially keen on talking about the advantages of third-dimension GIS
capabilities for representing the 3-D structure of urban environments and for
conducting 3D spatial analysis. Many of their tasks such as site selection,
emergency response, and urban management are being conducted in geospatial
context.
Data conversion
However, data conversion between these CAD/BIM and GIS systems is resulting in
a enormous mismatch that are require a manual work to be undertaken, due to
limitations associated with exchange of data and knowledge. In 3D, spanning a
bridge between CAD and GIS is even more challenging.
This is due to the following facts: existing CAD and GIS platforms have been
developed independently with different purposes resulting in significant
differences in terms of data formats they support, terminology they used,
semantics of concepts they represent, reasoning techniques on which they are
based, different scale representations, and transformation of the local (CAD)
coordinates into reference system for both the horizontal and vertical
coordinates, geometry modelling in both systems, CAD software provides all
kinds of primitives to create geometric (and their visual attributes), it
represent objects with different representations such as CSG and Sweeping,
however these primitives are not supported in GIS (e.g. parametric primitives)
while geospatial models mainly use BRep as the main geometrical representation
method.
Figure 2 - SQL
statement runs a find ancestor function on 3D utility network.
CAD and GIS modelsFurthermore, CAD models usually do not store topologic
information which is in fact an important characteristic of geospatial models
(i.e. geospatial models use topology to store geometric information in a more
efficient manner)., For these reasons currently CAD and GIS platforms are not
interoperable.
Recently and as a result of the developed building standard such as Industry
Foundation Classes (IFC), the Integration between Geospatial information and
BIM/CAD could have been achieved at semantic level. Efforts deals with bridging
the gap between BIM/CAD and geospatial information models are providing
harmonisation of semantics that allowing the interoperability at the data level
and as web services. Current building models are capable to store
semantic information and spatial relationships of building elements in an
object oriented data structures.
Figure 3 - General view
of utility Application
As a result different tools are being developed that enable the transformation
of building models to be represented using 3D City data model standards (BIM
server 2009, IFC explorer, 2008) and thus enable the visualization within 3D
geospatial context using GIS software which provide stand alone or add on
extension which is limited for visualization purposes, and by doing so,
neglects spatial analysis, the very core of a GIS system.
In this paper we present a web based 3D GIS solution that allow integration of
the 3D building designs within 3D city models. Using the proposed
solution it is possible to perform geo-analysis and provide direct
visualization using geospatial browser, the system present a new concept to
store, process, analyze and visualize 3D building models within 3D geospatial
context including utility networks. Emphasis is laid on the integration of BIM
information without loss of information and to use it further beyond 3D
visualization - for spatial analysis.
BIM4GeoA (Building information for Geo-analysis)
This product is entirely built in an Open Source environment with components
(OSI – Open Source Initiative, 2010), which can be downloaded from the Internet
for free. The prototype named BIM4GeoA is composed of three components:
IFC Parser - The IFC parser is developed in php scripting language using
a combination of DOM and XML-reader libraries. The user can interact with the
BIM server and query specific building element; and, when the output is
delivered to the server as IfcXML file, the file is parsed on the fly and the
required information is extracted. The parser has conversion functionalities
that allow the translation of geometry representation from Swept Solid to
B-Rep, Moreover the IFC-Parser performs geometry transformation from local
coordinate systems to the real word coordinate system. After performing the
transformation operation, the parser inserts the building object into the
database as a 3D object. Figure 1 provides an illustration of parser running in
a web browser.
Analysis Functionalities - BIM4GeoA offers simple geometric and topological
analysis functionalities, the functions is implemented within PostgreSQL
environment. Most of the commercial DBMS enable users to create a new
user-defined data type and functions. In this research, the user-defined data type
and functions are written in PlpgSQL, These functions include:
GUI for Query and Visualization - To allow a system user to both
interact with and visualize the analysis result in 3D, a web site is customized
that can be accessed from any client’s PC or mobile device. It is organized in
two mainframes (Figure 2 & 3). The right frame include a drop-down menu,
which provides analysis functionalities and a text field to enter functions
parameters, while the lower part of the frame provides a space where the
textual result of the query displayed.
The 3D viewer is located in the right frame. It is based on the Google Earth
plug-in. Several functionalities was customized and added to the viewer using
Google Earth APIs, e.g. zoom-in and zoom-out, and a special functionality that
provides smooth movement and keys that allow the user to change the camera
view. The user can interact with the 3D view and click on any 3D objects and
get the attribute of this object.
The underlying technology
The system is developed using open source software and specifications. OSS is
defined as computer software whose license “permits users to use, change, and
improve the software, and to redistribute it in modified or unmodified form. It
is very often developed in a public, collaborative manner” (OpenGIS, 2010) they
present a healthy competition with proprietary software and may lead to
affordable pricing and increased access.
Figure 4 - General view of routing application, the optimum path between two
entities.
Among the well known OSS projects are the Linux operating system and the Apache
web server. As of January 2010, the open source GIS website has listed more
than 247 of GIS related OSS projects (OpenGIS, 2010) . OS promotes
interoperability through its pubic availability (OGC, 2010), it provide
software developers with information about a given specification as well as
specific programming rules and advice for implementing the interfaces and/or
protocols.
It allows the systems to work easily with each other and overcome tedious batch
conservation tasks, import/export obstacles (Anderson et al, 2010). Among OGC
specifications are KML and CityGML, two standards for 3D GIS. This section
provides background information about the origin, relationships among the OS
and OSS, and their relevance for the creation of the 3D geoprocessing web GIS.
Reasons for an open source information system
There is a growing interest in the use of OS, the term open source gains more
attention, the OSS market is growing rapidly; it is products fed by small
organizations and regional government agencies that cannot afford proprietary
software’s. The idea of creating the system based on OS emerged from the need
to address two sets of challenges.
Firstly, current commercial GIS software does not offer 3D functionalities,
developing a system with new functionalities is much flexible with OS,
developing such system based on commercial software is expensive and require
special training to become professional on their software operation and
maintenance. Moreover, Open standard and fully transparent software solutions
lead to a stronger cross linking of knowledge and data itself. Secondly, there
is a demand for a flexible and low-cost system, due to limited funding. License
fees have to be paid for commercial systems and spatial add-ons. Cost-saving
solutions are especially required by institutions with low budget.
System architecture, design and developmentsAn important phase was the
selection of the open-source software and technologies, where Different aspects
have been considered to select the appropriate OSS. We concentrated on mature
OSS projects with clear identification core development teams and wide
development and broad active users communities (particularly at the
international level). We also sought projects with well-established records of
success in developing simple prototype systems as well as large
mission-critical applications. Other important aspects were the available
resources such as books, user forums, user conferences, and online
documentation. After considering several options we decided to use the OSS
described below.
The key principle is to use existing functionalities and combine them in an
optimized way for the requirements of urban management (e.g. the visualization
capabilities of KML). CAD users can interact and update their design using a
building information server at the same time The GIS users can retrieve the
up-to-date CAD data and use it in the analysis. The current version of the
BIM4GeoA is the result of a first development cycle. Figure 5 presents the
system integration.
Google Earth plug-in is a JavaScript API that allows for the embedding of
Google Earth into web pages, and visualizes 3D models in standard web
browsers (Google, 2010). It provides powerful 3D web visualization
functionalities. KML (Keyhole Markup Language): KML is an XML data format that
has a tag-based structure with names and attributes to display geographic data
in an Earth browser, such as Google Earth. KML allows the definition of styles
to specify feature appearance, icons, and labels to identify locations. It can
also display textured objects. The KML file has been generated on the fly to visualize
the result of the suitable queries and the 3D model of the campus
building.Through java script code it is possible to adjust several
visualization properties of these models such as ‘hide texture’ and ‘change
visibility’.
PostgreSQL/PostGIS is a powerful, OSS object-relational database system,
supporting almost all SQL functions including sub selects, transactions, and
user defined data types and functions (PostgreSQL, 2010). The PostGIS extension
offers the capability to store spatial features with x,y,z coordinates and to
perform more than 80 spatial and geoprocessing operations including limited 3D
spatial analysis such as 3D BOX (PostGIS, 2010). It is used to process spatial
and attributes queries and to store the network and other building element as
spatial tables with its attributes. Pgrouting is a set of C++ libraries that
provide routing functionality to PostgreSQL/PostGIS. Its tools provide shortest
route functionalities for real road networks including considering restrictions
with heuristics. The tools are based on the well known Dijkstra shortest route
algorithm (Pgrouting, 2010).
Some modifications were performed on the Pgrouting functions to be able to
create a 3D topology (graph), and to perform the network analysis of the indoor
and outdoor spaces. This considers the different level of space (3D) and the
characteristics of the indoor environment such as door types, elevators and
stairs. PHP was used to create inter-application communication and to process
the user’s input and send it back to the web interface. An SQL query to the
attributes and the network that are stored in PostGIS spatial tables is built
using customized user interfaces, such as buttons, checkboxes, or text fields.
Figure 5 - Architecture of the prototype- BIM4GeoA
The query is then submitted to the server using an HTML form that captures the
user’s input. At the server, a PHP script converts the user’s input into
an SQL statement that is submitted to PostgreSQL/PostGIS for processing.
The geometry texts that are returned by PostgreSQL/PostGIS are converted to KML
code format using PHP and then visualized in the Google Earth plug-in. IfcXml
(Industry Foundation Class or IFC) has been developed by the international
alliance for interoperability (IAI) since 1994. It latest release is IFC 2x3.
The IFC 2x release has introduced the ifcXML specification by using XML schema
to define the IFC models in parallel with EXPRESS.
The target application of this standard is to provide a comprehensive
description of the building and the construction site (Nisbat and Liebich,
2005). CityGML is an OGC standard, which provides a specification for the
representation of 3D urban objects (Groger et al., 2008). The standard was used
as a guideline for organizing and mapping building objects in RDBMS.
BIMServer it is an open-source project enabling the centralization of the
information for a construction (or other building related) project. The core is
based on the open standard IFC, and therefore knows how to handle IFC data. The
BIMserver is not a fileserver, but uses instead the model-driven architecture
approach. The main advantage of this BIM server is its ability to query, merge and
filter the BIM-model and generate IFC files ad hoc (BimServer, 2009).
Conclusion and Outlook In this paper we present a valuable approach to
integrate BIM into more comprehensive 3D Geo-information System. The approach
is highly important to both AEC and geospatial industry. It is a combination of
open source of tools which used to create a vehicle to integrate BIM data (IFC)
into a user accessible 3D navigation and viewing environment, which also
provide some analytical operations- such as routing and utility network
analysis.
The prototype demonstrates the potential of using OS to provide highly
interactive 3D GIS applications on the web. Postgres/PostGIS provide a robust
database management system that offers a considerable and continuously increasing
number of 2D geoprocessing functions, the lack of 3D query/analysis capability
put some limitation on the options due to the current lack of 3D
functionalities (as compared to the 3D query/analysis capability provided in
the commercial software Oracle), specific data type as well as query
functionalities is developed to meet the requirement of these 3D applications.
Google Earth and KML standard proved to be an easy way to use 3D visualization
tools with powerful functionalities. Pgrouting libraries provide easy to use
function via PostgreSql/PostGIS. It is possible to modify these libraries to be
used in 3D network (non-planar graph) analysis. This could be demonstrated by
the feasibility of computing routes through graph theory and modified 3D Disjkstra
algorithms. Our future research will concentrate on implementing more analysis
functionalities required by the 3D application of web campus. In addition
the prototype will be open for use by the real campus community for
testing. Therefore, the system will be modified based on their feedback.
Acknowledgement
The financial support from the German Academic Exchange Service (DAAD) for this
work is gratefully acknowledged - See more at:
http://www.sensorsandsystems.com/article/features/16733-bim-for-geo-anal...