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Issue Date: December 2000

CATEGORIES

Mobile mapping on-demand - active representation and automated generalisation of spatial databases for the wireless handheld information appliance - Part I

December 2000
P.G. Hardy, Laser-Scan, UK

The Internet is going mobile and tomorrow’s user will expect to easily retrieve everyday information via his/her handheld wireless appliance (integrated phone plus browser). Much of this information will have a strong spatial component (where is the nearest?), and will need to be presented as some form of map. The constraints of the display size, and the on-demand nature of the information retrieval will require the use of active representation and automatic generalisation, to present the vital information to the user without unnecessary clutter. This paper analyses the impact of this new requirement on the cartographic business, and highlights the importance of active object technology in achieving the necessary presentation.

1. Introduction
1.1 The Internet as Information Source
Although the Internet has existed for over 25 years, it has undergone dramatic growth in the last five years, fuelled by cheap hardware and by the 'World Wide Web' as an application. The web itself is made possible by simple information access protocols such as http and html, which have led to the Internet becoming the major information repository for mankind. Aiding the take-up of the Internet as an information source has been the availability of free or very cheap web browser software (eg Internet Explorer or Netscape Navigator).
As the majority of human-related information has a location component, it is natural that map display should become a preferred way of finding and presenting information. This has led to the rise of 'web mapping', as exemplified in the CamMap site.
1.2 The mobile phone
If the growth of the Internet has been dramatic, that of the cellular telephone has been explosive. Dataquest, reported by news channel CNNfn, calculated that 283 million cellular handsets were sold in 1999, with the estimate for 2000 being 410 million. From almost unknown five years ago, it has now become a commodity item, carried everywhere by people from all walks of life. As well as its initial role as a person-to-person communication tool, it is rapidly gaining ground as a means of enquiring for information. There has been recent hype over WAP (Wireless Access Protocol).
The expansion of this information retrieval role is currently restricted by various physical limits, most of which will be eased by future technology already in the pipeline. The main such are:
* Display size and resolution - at the time of writing this is around 100 x 50 monochrome pixels, but new display technology will increase this dramatically, giving high resolutions, colour and foldaway displays. Voice synthesis is also an important alternative or complement to display for presentation of information.
* Keyboard size - small and getting smaller for ease of carrying. Voice recognition is the vital technology, which will help avoid the need for keying.
* Data download rate - for GSM, currently 9600 bps, but GPRS being deployed now gives 100 Kbps, and the G3 UMTS third generation licences recently auctioned will provide 2 Mbps.
* CPU speed - currently far less than in desktop or laptop systems, but Moore's Law says that such power doubles every 18 months.
* Battery life - improved a lot last year, but is in a fight against increased power consumption from better screens and faster CPUs. New battery technologies on the way will help.
1.3 PDAs, palmtops and GPS
The third strand of technology contributing to the information revolution is specialised handheld devices. The most common is a PDA (personal digital assistant). These handheld devices started out as electronic address books, but they have evolved into electronic equivalents of the Filofax. Examples include the Psion 5mx, Palm V, and Compaq Aero. Related but less portable devices include the palmtop computers, exemplified by the HP Jornada. These are more general computing devices, being scaled-down versions of laptops.
Other related devices are the GPS (global positioning system) receivers. These were bulky, but modern design is reducing them to very portable.
1.4 The wireless handheld information appliance (WHIA)
The future will bring a new generation of devices, which meld features from mobile phones, PDAs, palmtops and GPS to give a single optimal tool for communication and information retrieval. Such devices will become as common as the wristwatch is now. The capabilities of such devices can already be simulated by combinations of existing tools, such as using a PDA to access the Internet through an infrared link to a mobile phone to access on-demand mapping.
The acronym WHIA may initially seem inelegant, but when pronounced 'weir', it does have appropriate location connotations, as in the famous Yorkshire song 'Ilkley Moor' (Whia has tha bin sin I saw thee?)!
Although much more capable than any one existing handheld device, the WHIA will still have limitations enforced by the conflicting requirements of less weight, longer battery life against better screen, faster access. This means that intelligent presentation of information will become a vital lever for usability.
1.5 Where am I?
WHIAs of the future will always know where they are. Already any current mobile phone has to determine its geographic position relative to the cellphone network transmitters in order to hand over from cell to cell while travelling. Refinements to this location technology like Cursor from Cambridge Positioning Systems will give positions accurate to 25 m in the open, and to a metre or so in dense areas like shopping malls.
Satellite positioning (GPS) is an alternative technology, which gives better results in open areas (it recently became 10 times more accurate because a military scrambling called SA was turned off). GPS is not so good in cluttered areas like city centres where the signal from the sky is shielded or confused by echoes. Future WHIAs will probably use a combination of techniques to always track their position to a few metres.
Having such location information available is a necessary starting point to the set of questions:
* Where am I?

* Where is the nearest...?

* How do I get to...?
The answers to such questions can be given by various techniques:
* Synthesised voice ('at next junction, turn left').

* Human operator voice ('turn left after the Pig and Whistle').

* Text messaging ('in 250 m turn left, then ...'

* Graphical map displayed on screen.

* Graphical map plus instructions sent to paper by fax.
However, in all such cases, the primary source of answers will be a geographic information server. This paper contends that an active object database is key to finding and presenting the requisite geographic information in a clear and concise manner.
2. Active objects
2.1 What are active objects?
The object-oriented (O-O) paradigm has been sweeping through the software industry for many years. O-O is a logical way of modelling the real world within a computer software system. All modern software-engineering languages (C++, Java) are built around the four key O-O concepts, of encapsulation, referencing, inheritance and polymorphism.
* Encapsulation means that data and behaviour are not separated, but encapsulated together within objects that respond to messages sent to them.

* Referencing means that objects can have direct knowledge of related objects (a river 'flows from' a spring).

* Inheritance means that the object classes can gain capabilities from multiple superclasses, such as canals inheriting from 'transportation', and from 'water'. This allows modelling the family structure of the real world (a church is a kind of a public building, which is a kind of a building, which is a kind of a man-made structure).

* Polymorphism means that different classes can respond to the same message with an appropriate behaviour (click on a factory and click on a road, and get different description types and different highlighting).
A new generation of spatial database, GIS and mapping systems is adopting O-O concepts and applying them to storage, retrieval, analysis and display of location-related information. This paper concentrates on the Laser-Scan Gothic family of spatial software, built around the Gothic O-O spatial database. More detail on this family is available in the paper on 'Active object techniques for production of multiple map and geodata products from a spatial database'.
2.2 Characteristics of active object spatial database mapping system
A Gothic database mapping system has the following characteristics:
* Object database - provides efficient storage and retrieval of spatial objects.
* Object data model (Schema) - allows modelling of the real world entities and their relationships.
* Continuous mapping (no sheet boundaries) - provides the area wanted at the scale requested.
* Object database views allow intelligent selection of subsets of objects for current purpose.

* Active representation provides good cartography (see below).

* Active object generalisation methods derive appropriate map features for current scale and need (see below).

* Validation methods ensure data integrity.

* Open architecture allows access from workstation, desktop, web browser, or WHIA.
3. Active display
3.1 Display methods
A key aspect of O-O mapping is the use of display methods for all visualisation. Instead of the application having fixed rules about representation, or using a static table of styles, all drawing is done by sending a message to each relevant object saying 'draw yourself'. The response to the message is to execute the object's 'display method', which can use the power of the object database and spatial toolkit to decide what to do. It can:
* Decide to draw or not to draw itself, dependent on scale, specification, and surroundings.

* Use a rich set of representation styles (line patterns, area fills, symbols).

* Change type according to scale - an area object may draw itself as point symbol if it is too small at this scale.

* Use a different 'geometry' (shape) according to scale, showing less detail at smaller scale.

* Draw itself more than once in different styles, eg to achieve road casings, or text labels.

* Move itself into clear space to avoid edge of map or other collisions.

* Modify its representation according to scale and surroundings; eg shorten text label to match length of road.
The technology discussed in this article is available through Racal Aviation Systems, (021) 936 8100, gis@resa.co.za
Part II: April 2001


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