DSpace at VNU: On the development of three dimensional WebGIS systems: Some new trends and prospects

We also exemplify one operation attached to the spatial analysis- oriented WebGIS-3D system which is considered to be one of the most striking trends above.. Among them, we argue that

On The Development of Three Dimensional WebGIS Systems: Some New Trends and Prospects

LeHoang Son Center for High Performance of Computing HaNoi University of Science, VNU

Ha Noi, Viet Nam sonlh@vnu.edu.vn

Abstract- The applications of three dimensional WebGIS

systems are currently receiving growing interest from

researchers with various backgrounds In this paper, we will

discuss about some new trends as well as prospects of these

applications in the future We also exemplify one operation

attached to the spatial analysis- oriented WebGIS-3D system

which is considered to be one of the most striking trends above

The result shows great potential of them to capture the

attention of researchers in nearly future

Keywords- Virtual Reality, WebGIS-3D, Information System

The synergy of Geographic Information Systems and

Web Technology allows access to dynamic geospatial

information without burdening the users with complicated

and expensive softwares The World Wide Web provides

GIS users easy access to spatial data in a distributed

environment through a simple browser interface or

sometimes by a lightweight client side application The

concept of Web GIS is based on how the map is produced

and responds to users' interactions over the Web It becomes

more important when the location-specific information is

dynamic and decisions have to be made on real time basis

Examples are the market prices of commodities of various

markets, the stock and supply-chain management, real time

weather information, real estate, asset management and asset

tracking, agricultural land management etc The three

dimensional WebGIS system is a higher development than

previous GIS-2Ds and originated from the fact that people

want to enhance the visualization of GIS WebGIS-3D can

provide realistic visualization of spatial information and has

immense potential in infrastructure management (life-line

and network infrastructure), disaster management and

geological modeling, etc It is considered to be the main

focus of GIS scientists nowadays [1] Recently, these have

been some trends to develop three dimensional WebGIS

systems with the purpose to adapt a variety of complex

requests in natural and social science Among them, we

argue that three striking trends: Semantic Sensitive- based,

Spatial Analysis- oriented and Real time WebGIS-3D have a

great potential to occupy an important position in

WebGIS-3D researches in the future We also provide one spatial

analysis operation as the exemplification of spatial analysis­

oriented WebGIS-3D systems' functions as they are getting

important in science as well as actual needs nowadays

The rest of the paper is organized as follows Section 2 presents three developments of WebGIS-3D systems We will present one additional spatial analysis operation for spatial analysis- oriented WebGIS-3D systems in section 3 Finally, we make conclusions in the last section

APPLICATIONS

A Semantic-Sensitive WebGIS-3D

Geospatial data semantics deal with representations of geographical world as interpreted by human users or community of practitioners Representation and reasoning on the meaning of geospatial data are critical for the development of interoperable geospatial data and software, geographical information retrieval, and automated spatial reasoning Recent progress on semantic geospatial web raises the need to make spatial data semantics explicit and available to search engines However, it is extremely difficult

to capture and maintain semantic knowledge of geographical data due to the complexities of geographical categories, geospatial languages and heterogeneous, multimodal, and multimedia representations of spatial data At the moment, GIS systems either impose simple semantic structure a-priori

or do not address the issue of semantics at all but simply offer textual metadata description, leaving the burden of meaning construction to the user Such solutions (or lack of it) are extremely inadequate to the current stage of geographical information technologies where massive exchange of data from heterogeneous sources must be supported

Let's consider a simple scenario that highlights the need for contextualization of spatial data semantics Suppose that

a person approaches a computer and asks for a map to be displayed by saying: "Show me a map near SC town" The computer is expected to understand this request and compile

a map that matches with the user's conception of 'near' In order to process this request, the system has to understand a number of concepts First, it has to understand that 'SC town' is a geographical entity with geographical location, area extent, boundary (although can be vaguely defmed), and numerous other characteristics Second, it needs to understand what it means by 'near' 'Near' is a basic spatial concept that should be part of the ontology of geographical space However, 'near' does not correspond to any fixed set

of geographical entities Instead, what part of the earth

surface that qualifies as "near SC town" depends on the

actual context of the map request Is this in the context of

grocery shopping, or planning a vacation, or locating a new

business office? If this is about grocery shopping, are we

talking about driving a car, riding a bike, or walking? Figure

1 illustrates the idea that a person may well have two

different senses of near ('Near I" and ''Near 2") for two

different travel modes (drive or walk) in grocery shopping

N�ar I

drin " lr ' "

N�ar2

->

Grocery shop Figure I A simple scenario

This is a case of semantic interoperability between a

human being and a computer Human and computer are

fundamentally different conceptual systems, and they

maintain quite different ontological commitments on the

geographical space Human conceptualization of space

follows the 'cognitive' view of the space, while computers

(as formal systems) follow the 'scientific' view of space The

scientific view, which is the basis for GIS representation of

space, treats geographical space as a seamless and uniform

space where a set of spatial concepts applies to all scales and

all phenomena In contrast, human's cognitive categories and

concepts about space come from their experiences of

interacting with the world in a variety of tasks and activities

Such knowledge can only be acquired piece by piece since

geographical space is too large to be experienced all together

People view the same spatial situation quite differently

depending on the actual context and purpose Human spatial

knowledge are incomplete, biased, vague, and sometimes,

inconsistent A data object has no unique and correct

meaning; instead, semantics are interpreter dependent and

context-bounded

Authors [3] introduced a novel approach for mediating

semantic interoperability in human-GIS dialogues It was

based on ideas of contextualized ontology and context­

mediated behavior that are well-established in the literature

Contexts are captured as first class objects and represented

together with ontology base They used context schemas to

guide GeoDialogue in monitoring context change and

generating context-appropriate maps Human-computer

dialogues benefited from formal reasoning on context, and at

the same time, provided a communication channel to gather

and share contextual knowledge

Another semantic GIS- approach came from [8] The

research presented in this paper introduced a context-aware

mobile GIS that integrated adaptive interaction principles

and techniques They defined an adaptive GIS as a GIS that

was able to automatically derive its content and interface from a changing environment An adaptive GIS allowed to present relevant information to the user, and improve the usage and usability of the information provided according to the context The contextual dimensions were of different nature as they involved geographical data, computing processes and interfaces, and user categories These contexts influenced, to a certain degree, the way geographical data and processes were delivered in wireless environments Adaptive GIS could be considered as a representative of the emerging trend of personalized software, that has been the object of considerable attention over the recent years From semantic human-GIS interaction to context-aware mobile GIS, the semantic approach is getting more and more important to GIS systems in general Along with the innovation of computer graphics nowadays, the combination

of GIS-3D especially WebGIS-3D systems with semantic approach is no longer an unrealistic dream In the nearly future, we will be acquainted with personalized WebGIS-3D systems where GIS data vary according to context or answer machine based on semantic WebGIS-3D as well as many other applications useful for societies

The slogans of today's world is 'time is money' This shows the value of time in our all day life Furthermore, about 80% of all data are somehow spatial related and most users have experiences with maps, being a simple and intuitive kind of visualisation for complex spatial themes This leads to the idea of using map-based visualisations and GIS in time critical applications (e.g emergency management) Time-critical applications (TCA) [11] are related to decisions that have to be made by a human decision maker in emergency situations Figure 2 shows an example of such an architecture considering an emergency management scenario For such TCA it is necessary to even

be independent of the location of the decision maker when he/she is asked for his decision For example, one never knows when a case of emergency occurs and one hardly would know where a decision maker would be

Technical environment

Figure 2 An emergency management

Real-time data refers to spatial and non-spatial data that becomes available to the real-time GIS, either at fixed time intervals or after the completion of certain events such as the arrival of data at a desired destination Conventional GIS models such as data modelling, data management, and

software design and engineering do not allow current GIS

systems to meet the requirements of real-time applications

effectively For example, the key requirement of real-time

flood forecasting, however, is based on continuous in situ

measurements of rainfall to improve the accuracy of model

forecasts While there have been significant advances in the

accuracy of quantitative measurements and the forecasting of

rainfall using weather radar and more prolific and

sophisticated rain gauge networks, extensive research efforts

are still required to develop systems that incorporate real­

time data with a GIS application so that real-time data can be

obtained with sufficient timeliness and rapid nowcasts can be

produced Authors [12] proposed a real-time hydrological

model for flood prediction using GIS and the WWW The

purpose of this study was to examine the current status of

real time hydrological models used for flood nowcasting and

hazard mitigation and indicated how WWW-based systems

can overcome some of the limitations of existing systems

Whilst hydrologically innovative and robust models were

available, they were poorly suited to real time application,

were often not well integrated with spatial datasets such as

GIS Current systems also lacked flexibility, customisability

and accessibility by a range of end users This paper also

described the development of a Web-based hydrological

modelling system that perrnited integrated handling of real­

time rainfall data from a wireless monitoring network A

spatially distributed GIS-based model is integrated on the

basis of this incoming data, approximating real-time to

produce data on catchment hydrology and runoff The data

can be accessed from any WWW interface, and they can be

analysed online using a number of GIS and numerical

functions

The advances of visualization techniques and city

modelling trends in recent years have been arising the idea of

historical GIS based on real-time three dimensional WWW

Paper [5] has presented the Virtual Kyoto- a 4DGIS city

comprising spatial and temporal dimensions Virtual Kyoto

is a virtual time-space created on a computer for the purpose

Figure 3 3D city model of Kyoto

of investigating the past, present and future of the historical

city of Kyoto Using the cutting-edge technologies in GIS

and VR, they build Virtual Kyoto which is 4DGIS that

comprises a series of 3DGIS at different points in time The

3D city modeling begins with the present Kyoto and then

goes back to the past, including those soon after and before

the World War II, the Taisho and Meiji eras, pre-modem Edo era and finally back to Heian era when the city of Kyoto was founded in late 8th century Creating Virtual Kyoto includes the following projects: a) Archiving geo-referenced materials such as current digital maps, old topographic maps, cadastral maps, aerial photos, picture maps, street photos, landscape paintings, archaeological sites data, and historical documents; b) Creating a database of all existing buildings including machiyas (traditional town houses),early modem buildings, shrines and temples including historical and cultural heritages; Creating 3D VR models of the above buildings; and d) Estimating and simulating land use and landscape changes over the study periods using aforementioned materials Virtual Kyoto is an infrastructure

to place various digitally archived materials associated with the city, and to disseminate Kyoto's subtle and sophisticated forms of cultures and arts to the world over the Internet The web-based system provides user-friendly interface to explore historical materials of cultures and arts in the geographic context of Kyoto with its historical landscapes Virtual Kyoto plays a valuable role in the assistance for urban landscape planning of Kyoto as well as sending rich information about Kyoto to the world through the Internet

On the anniversary of 1000 years Thang Long- Ha Noi city will be held on October 20 I 0, the working group of Virtual Kyoto has started a project recovering and reappearing ancient Thang Long royal citadel along its history Obviously, real time GIS applications especially historical WebGIS are getting more and more important Sooner, we will have the opportunity to observe 3DGIS museums which are truthful evidences of history of mankind

The last striking trend in this paper is Spatial Analysis Although it was not the focus of GIS systems at the first time, people's conception, however, have changed since the workshop at the University of Sheffield, 1991 on the issue associated in putting data analysis techniques into GIS to the mutual benefit of both field [7] This workshop elicited some problems and challenges in spatial analysis Spatial Analysis (SA) is a set of techniques devised to support a spatial perspective on data To distinguish it from other forms of analysis, it might be defined as a set of techniques whose results are dependent on the location of the objects or events being analyzed, requiring access to both the locations and attributes of objects Its techniques range from simple descriptive measures of pattern of events to complex statistical tests of whether a set of events could have been generated by specific, well-defmed, processes Note that SA

as defined here does not include techniques that use only attributes of objects

There are many applications that use spatial analysis techniques for their own specific tasks For example, Black men who have sex with men (MSM) are a priority population for HIV prevention Authours [10] applied spatial analysis techniques to map the availability of HI V prevention services to young black MSM in Chicago to guide prevention planning GIS was used to map characteristics of ZIP codes in Chicago Choropleth maps and descriptive

statistics were used to visualize and analyze the data The

results showed amazing effects: Areas where young black

MSM reside typically have low HIV service densities HIV

service density also corresponds poorly to some ZIP codes in

which young black MSM who report high rates of

unprotected sexual behavior reside Therefore, Spatial

analysis can show whether services are located near specific

populations of interest or not Data from multiple sources can

be integrated to explore relationships among characteristics

of geographic zones Another example was from [4] who

used Spatial Analysis for Air Pollution and Mortality in Los

Angeles The assessment of air pollution exposure using only

community average concentrations might lead to

measurement error that lowers estimates of the health burden

attributable to poor air quality After testing this hypothesis,

they suggested the chronic health effects associated with

within-city gradients in exposure to PM2.5 might be even

larger than previously reported across metropolitan areas

They also found specificity in cause of death, with PM2.5

associated more strongly with ischemic heart disease than

with cardiopulmonary or all-cause mortality

To support for researches in natural and social science

using spatial analysis techniques, a lot of solutions have been

proposed One of them was GeoDa- a free software program

intended to serve as a user-friendly and graphical

introduction to spatial analysis for non-geographic

information system (GIS) specialists [6] It includes

functionality ranging from simple mapping to exploratory

data analysis, the visualization of global and local spatial

autocorrelation, and spatial regression A key feature of

GeoDa is an interactive environment that combines maps

with statistical graphics, using the technology of dynamically

linked windows Some illustrative examples that highlight

distinctive features of the program in applications dealt with

public health, economic development, real estate analysis,

and criminology Besides, the development of Internet also

put GIS scientists in a new challenge of GIS systems and SA

Authors [2] presented SANET- a Toolbox for Spatial

Analysis on the network This study showed a GIS-based

toolbox for analyzing spatial phenomena that occur on a

network (e.g., traffic accidents) or almost along a network

(e.g., fast-food stores in a downtown) The toolbox contained

13 tools: random point generation on a network, the Voronoi

diagram, the K-function and cross K-function methods, the

unconditional and conditional nearest-neighbor distance

methods, the Hull model, and preprocessing tools The

article also showed a few actual analyses carried out with

these tools

The most fashionable trend in SA, perhaps, is studying its

techniques in three dimensional WebGIS systems Paper [9]

proposed some interactive functions for geometric and

metric analysis in 3D terrain of Tahoe Lake, USA using

javascript nodes in standard VRML such as vertical

exaggeration, moving secant plane, measuring the distance

between two points, showing 3D buffer, These operations

were implemented in 3D maps having 'real' coordinates

system and useful for measurement tasks Although it was

quite simple, people considered it the first and clear evidence

of SA techniques in three dimensional GIS in WWW These

techniques are widely applied in many branches and the first step toward a spatial analysis- oriented WebGIS-3D system For the benefit of sharing GIS data, free-use and convenience, the study of WebGIS-3D and SA techniques on it is becoming one of major researches in nearly future

Figure 4 blast simulation using SA technique in 3D WebGIS

III EXEMPLIFICATION OF SPATIAL ANALYSIS

Consider the situation that we have a 3D terrain which contains a lot of lakes or ponds cutting through mountains How can we calculate the area and perimeter of these lakes

or ponds? If we have relative approximations of them, we easily illustrate the lesson in class or utilize this method for some measurement tasks without going out field trips In this scene, we continue to develop a spatial analysis operation based on the idea of [9] This operation implemented with geographic modelling language Geo VRML and scripting language Javascript, along with other SA techniques in that paper, are the basis to construct a spatial analysis- oriented WebGIS-3D

The essence of the problem turns back to calculate the area and perimeter of secant plane between the plane y=a and 3D terrain Due to the secant plane can be a variety which is convex or self-cutting or in any form of shape, this secant plane can be approximated by the minimal rectangle that consists of it Let's divide the plane y=a into a grid having numbers of dividing points and unit of length are equal to those things in elevation grid Indeed, we can calculate the area and perimeter of the secant plane through numbers of rectangular cell in the above plane The remain question is specifying whether a rectangular cell is inside the secant plane or not One important thing we should note that there exists cells in elevation grid which are over or under the plane Futhermore, one cell in the elevation grid is equivalent to one in the plane Therefore, if any cell in the elevation grid whose height is greater than related one's height (value a) then the related cell is inside the plane for all cells in the elevation grid This can be done by verifying the height of 4 top points of examined rectangular cell in the elevation grid to ensure all values are greater or equal to value a

After counting the number of rectangular cell inside the secant plane, the final area can be approximated by area of one cell multiplied by that number For the final perimeter,

we must provide one more thing: we examine 4 neighbours

of the specific rectangular cell and check whether it's

neighbour is outside the secant plane or not If it happens, the

common edge between 2 rectangles is the boundary We

totally calculate the final perimeter through the number of

boundary in X and Z axises

l ri,m ' T· 1286 929298400S79k m

Figure 5 Calculation of Area and Perimeter of lakes

In the experiment, we tested this operation with 3D

terrains in various Elevation Grid 's sizes (Figure 7) The

results show that: If we increase the size of Elevation Grid

then accuracy level is higher but the running time is slower

We can not avoid errors due to the approximation

Sometimes, we have to choose the optimized solution in both

accuracy and time The intersectional point between 2 lines,

perhaps, is the suitable solution in this context

Obviously, we can perform various visual calculations

through spatial analysis techniques As we mentioned above,

these techniques are implemented in WWW enviroment

which are easy for sharing and accessing Although, the

accuracy of this operation is not too high, however, this is

the first step toward a complete spatial analysis- oriented

WebGIS-3D system Later, it is no doubt that some solutions

to improve the accuracy as well as spatial analysis

techniques will be studied carefully In the nearly future, we

will see the period of SA- oriented WebGIS 3D systems

which appear in education, civil engineering, and many

other branches

The Accuracy and Running Time of SA operation by EG's Sizes

1400

Accuracy (m)

1200 Running Time (5)

HXXl

:§: 800

!:i

Jt 600

400

200

2Ox35 24x36 40x43 45x46 GOx54 8Ox75 120x115 2OOx180

Sizes of the Elevation Grid (km2)

Figure 6 The Accuracy and Running Time of SA operations

This paper aims to give a brief introduction about three major trends in studying three dimensional WebGIS systems namely as semantic-sensitive, spatial analysis- oriented and real time WebGIS 3D in recent years We also discuss the development flow as well as some state-of-the-arts applications in these trends to describe why they grasp the whole attention of specialists in various branches nowdays

We strongly believe that these trends will be widely studied

in the future Besides, we exemplify our Spatial Analysis­ oriented WebGIS-3D point of views by adding one spatial analysis operation to calculate area and perimeter of lakes or ponds cutting through mountains in the basis of 3D terrains

in WWW enviroment This operation is useful to illustrate the lesson in class or other measurement tasks

In the future, we will focus on constructing a spatial analysis- oriented WebGIS-3D system to utilize all pre­ studied operations for the need of science and socities

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