Mobile Mappers: Features and Applications

Mobile Mapping devices are a typical result of the on-going miniaturisation of instruments enabled by chip technology and electronics which result in small, handy, portable and accurate GPS tools that can be used hand in hand with survey instruments. Their many beneficial features potentially pave the way to success through adoption by a rapidly expanding GIS market. The author highlights characteristics of Mobile Mapping Devices and considers their application.

Geo-ICT professionals have over the course of time developed many advanced methods for storing, retrieving, processing and disseminating over the Web impressive amounts of geo-information. These developments in GIS technology have often been the subject of articles in this journal. Reading all these stories as a land surveyor sometimes leads to odd feelings popping up. Nice technology, one remarks to oneself, but what about the data? Who should be collecting it all? Which devices are actually capable of producing such huge amounts of data? And does a GIS user not care about the quality of the data he/she uses and the quality of the geo-information ultimately produced? GIS users are beginning to see that the demand for accurate, detailed and timely geo-data is increasing alongside the increasing use of GIS throughout all sectors of the economy. The surveying world recognises the needs of the GIS user and is continually looking for ways in which the latest technology can be employed to serve them. One spin-off of all this is the mobile mapper.

From Two Domains
Basically, a mobile mapper integrates GPS, GIS, geo-database and mapping in one compact handheld device. This new technology may be approached either from the surveying/navigation domain or from the GIS domain. Coming at it from the GIS domain, GIS companies deliver software – ESRI calls theirs mobile mapping and GIS – which provides the mobile mapper with a whole suite of GIS functionality. This includes map navigation (zoom/pan, centre on the current GPS position), geometric computations such as distances, areas and bearings, display, editing, updating and collecting, storing and mapping of GPS measurements, and adding attribute values to collected point, line and area features. Coming from the survey/navigation domain focuses attention on the GPS measurement aspect, and the fact that surveyors often have to operate in harsh work environments, leading to shock-resistant and waterproof devices. The software offered here is not usually a complete mobile GIS, but is designed to communicate with GIS packages either by transferring field recordings to the GIS system in the office or by downloading existing maps to the mobile mapper. The marriage of these two domain approaches in one handheld device provides both professional and casual field surveyors with an ultimately flexible solution. More importantly, it enables any mobile work force to collect accurate positioning data and the characteristics of fixed assets, which can then be used to manage those assets.

Beneficial Features
Like mobile phones, Mobile Mapping Devices have many beneficial features that potentially pave the way to great success, in particular in the still rapidly expanding GIS market. A mobile mapper enables a user to carry into the field an old terrain situation in need of updating, or a digital basemap on top of which certain features such as street furniture have to be mapped as a separate database. To the recorded features of points, lines or polygons, user-definable attributes can be assigned as appropriate to the mapping task in hand. A coding library can be predefined and downloaded prior to going into the field. The user interface is made such that anyone who can operate a mobile phone can operate a mobile mapper. Computer-literate layman can learn to operate the system in less than a day. The internal storage capacity is usually expressed in Gigabytes. This huge storage capability, together with convenient communication ports, enables (down)-
loading and provides instantaneous access to layers of topographic maps, large-scale base maps, aerial photos, high-resolution satellite imagery and land-ownership boundaries. Further, because of the complete digital storage of data and direct registration of the position in coordinates in any preferred coordinate system, either predefined or user-defined further processing can be done without overmuch human interaction, resulting in a high ratio of automation.

Built for Survival
The construction of the device is based on chip technology and electronics; unlike in total stations, there are no mechanical or optical parts, resulting in very favourable features, including portability, lightweight (typically less than 1kg, or about 500g), small size and handiness. Holding in the hands such a tiny instrument one wonders how something so small can possibly accommodate so many facilities! From the surveyor’s perspective, the heart of a mobile mapper is GPS. GPS is immune to concerns such as darkness and rough weather, and allows a person working solo to do the job. Depending on the measuring mode, a high order of precision can be achieved. From a GIS-user perspective, quick transfer to a GIS, by cable or Bluetooth, in a common datafile format, is a valuable property.
When purchasing a mobile mapper it is important to check such things as whether the device will survive:

• tumbling out of the surveyor’s hands towards a crash encounter with paved ground
  
• storage in a car standing the whole day in desert sun or polar cold
  
• plunging into a ditch full of water
  
• a life-long stay in a tropical rainforest.

Further issues concern whether the display is full-colour and readable in daylight, whether the battery can be charged from a vehicle or replaced in the field, and if it can last a whole working day.

Double Terminology
Communication among professionals requires a proper set of terms to identify equipment and specify methods. Accordingly, the introduction of new products and tools is usually associated with novel terms. The choice of a proper term is one issue, but a bigger one is that manufacturers may develop the same technology simultaneously whilst introducing differing terms. On the other hand, two different devices may be given the same name. This is the case with the term ‘mobile mapper’. In European countries the prefix mobile is a use-driven term chosen in analogy to mobile phone: compact, handheld devices which can be easily carried around. In the US, where such phones are referred to not as ‘mobile’ but as ‘cellular’ (a technology-driven term referring to the type of network necessary for wireless communication), the word ‘mobile’ refers to the mobility of a platform carrying surveying equipment. More particularly, it implies a van equipped with GPS, IMU, digital stereo cameras and laser scanners and able to determine real-time or, after post-processing, 3D position of features of interest found on and along the route. Sometimes a manufacturer may even be so happy with the choice of a term that he decides to register the name as a trademark (TM), as Thales did with the MobileMapper.

Crucial Accuracy
For many applications, such as mapping pipe-lines, good accuracy is crucial. The achievable accuracy of a mobile mapper does not depend so much on the device itself but more on the chosen GPS infrastructure support. When no use is made of any such support, so that one is operating in the stand-alone mode, accuracy is usually limited to about 3 metres. But by making use of various types of differential GPS, as supported by national or continent-wide GPS services, accuracies at sub-metre and even decimetre level are achievable. So accuracy depends mainly on what is paid for in terms of infrastructure services or, in some parts of the world, on the availability of these.

Tool for the Surveyor
Many land surveyors today use Mobile Mapping Devices to ease their lives. For example, the survey department of Lawton, Oklahoma, US, has been using them now for about two years for carrying out boundary surveying, GIS data-gathering for departments of public works, infrastructure and others, and geographic management of all survey and engineering data. Both for mapping and updating, the mobile device enables up to tenfold reductions in surveying time as compared to conventional methods. Using a base-station allows sub-foot accuracy 99% of the time in post-processing. So that Mobile Mapping Devices can be real time-savers for the land surveyor, whilst also offering good accuracy.

And on the Bike
Recreational biking is a popular leisure activity in The Netherlands. The Royal Dutch Touring Club (ANWB) in Den Haag has grouped together into sign-posted bicycle routes many roads leading through attractive landscapes. At the junctions of these, forming a still-expanding network covering the entire country, are placed signs and information boards. A database has been created containing information on routes, signs and boards. The field collection of this data has been done using Thales MobileMapper. To assist the field staff, a coding library containing all relevant details of place, route, area and other applicable features were loaded into MobileMapper Pro prior to data collection. After using Rinex to post-process data available from the AGRS stations (Dutch Cadastre Stations - Apeldoorn), the positional accuracy of all features lies within 70 centimetres. Further processing and analysis of data is done in ESRI’s Arcview.

Unmapped Terrain
The above examples refer to terrain of which maps have been produced at feasible scales. However, in many countries, large and medium-scale maps have either never been made or, if in better times they have been produced, perhaps half a century ago, they have since become desperately outdated and are hence of very little practical value. The suitability of Mobile Mapping Devices for use in unmapped terrain was demonstrated during bathymetric survey of the Senegal River in June 2004; with a length of 1,800km, the river flows west from Mali to form the border between Senegal and Mauritania. An essential prerequisite for bathymetric surveys is a map of the vicinity of the river. Mobile Mapping Devices proved themselves a good replacement for non-existent maps. Two crews drew the map of the river digitally, one day at a time, collecting data along the riverbanks and working one day ahead of the bathymetric survey vessels. At the end of each day data was downloaded in SHP format for use next day by the hydrographers. The outline of the riverbank was mapped at the rate of 80km per day.
Other applications fields where Mobile Mapping Devices may be of great help are in:

• mapping enumeration areas for national census
  
• accident mapping: evidence gathering for reconstructing the accident scene
  
• wild-fire suppression and management for navigating to the scene of a fire, directing fire fighters and ensuring safety at the scene, and afterwards mapping the damaged area.

Acknowledgement
The support of Thales Navigation in providing examples of applications is thankfully acknowledged.