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From CAD User AEC Magazine  Vol 22 No 3 - FEBRUARY/MARCH 2009

David Chadwick looks at the source of the terrain datasets used extensively by architects, civil engineers and environmental agencies - amongst others!

Intermap certainly chose the right day to demonstrate their affinity with the English landscape - by taking a group of journalists across a variegated bit of terrain in a couple of Land Rovers in deep snow! Called the Land Rover Experience, it was preceded by the Volvo experience - driving up on one of the worst days of the winter from West Somerset to Milton Keynes!

The trip was well worth it though, as I learned a whole new set of acronyms, and got to find out how Intermap managed to increase the amount of terrain data they were able to deliver for a given plot of land - in a reduced file size!

For that’s the business that Intermap Technologies, Ltd, is in - mapping the UK to unprecedented levels of accuracy. They arrived in the UK five years ago, and promptly produced their initial NEXTMap Britain in 2003, which is the basis of many geospatial projects in the UK's GIS, government and commercial sectors.

The purpose of the press event was to introduce two new products which have been developed from the NEXTMap dataset - NEXTMap Britain 2 and OTMs, or optimised triangulated irregular network (TIN) models. TINs are, of course, the primary point mapping device for all terrain mapping software.

NEXTMAP BRITAIN 2

The accuracy provided by the original NEXTMap Britain 1 (NMB1) dataset encouraged its use in a wide range of projects requiring cost-effective and accurate data. More recently, however, greater concern about development in flood-prone areas and along watercourses has prompted Intermap to come up with even better vertical accuracy. The company has actually been working with the Environment Agency, reverse engineering its LIDARbased dataset for its flood plain planning.

Higher-quality surfaces are required to produce DSMs (Digital Surface Models) which combine the ground surface with man-made features on it, and DTMs (Digital Terrain Models) which show just the ground - as opposed to DEMs, which are merely Digital Elevation Models.

To achieve greater accuracy with its datasets, Intermap has fused highresolution LIDAR data with its IFSAR (interferometric synthetic aperture radar) data. This has enabled Intermap to combine the strong points of each to produce an ideal solution, optimising resolutions, noise levels and shading capabilities.

The purpose is not only to display the contours of hills more accurately, but, if necessary, to pick out details such as roads, buildings and other features more easily. LIDAR provides more detail and accuracy than IFSAR, but is beset by signal noise. IFSAR comes with less noise, but also with less detail.

The combined solution also provides a facility for producing 3D terrain models from the datasets. The nominal vertical accuracy of the original NMB1 software is 1 metre RMSE (Root Mean Square Error - don't worry about it!) and 0.7m in the SE of England. In NEXTMap Britain 2 that accuracy has been increased to between 25 to 40 centimetres (0.25 to 0.4m). Coverage to date extends to about 80,000 square kilometres, in England and Wales.

By what seems to be a sleight of hand, they have used original NMB1 data, blended it with IFSAR-derived data and decimated the result to a 2metre grid. They then reprocessed the data, resampling it to the final 5 metre resolution, but incorporating the new 25cm accuracy in its Z co-ordinate! And, in doing so, producing DSMs and DTMs with a greatly enhanced level of detail. Individual 10x10km2 tiles at the new accuracy enable the NMB2 data to be no larger than 16Mb in size, and suitable, therefore, for use with web-based applications, as well as SAT Nav and other mobile mapping devices.

OPTIMISED TIN MODELS

OTMs provide the basis of all terrain maps. Triangulated irregular networks (TINs) are vector-based surfaces, derived from triangulated nodes with coordinates in three dimensions and interconnecting lines arranged in a mosaic of triangles.

Optimised TIN models take the process a step further. The original data comes from Intermap's DEMs (Digital Elevation Models), but the points of an optimised TIN model (OTM) are based on calculations that, intelligently, determine which are necessary to accurately represent the terrain.

Again, the process is able to produce a data file smaller in size than it would be using raw TIN data - accurately portraying 3D data, and ignoring TIN data that doesn't conform to the surface. With increased use of 3D visualisation, particularly in planning applications and the like, optimisation provides for the capabilities of graphics cards and incorporates water masks used to account for water bodies. This means that operators unfamiliar with, or who do not have access to such additional data, can save time and money while devoting valuable time to other aspects of their projects.

TIN datasets are widely used in conjunction with many applications, such as landscape modelling, architectural visualisations, engineering

and design mockups, SAT Nav and PDA applications, and even computer games and military simulations, where virtual topography can be introduced based on real-world data.

The use of OTMs greatly enhances the integration of DEMs in image or CAD- based applications, enabling users to show how structures interact with landscapes, not only in static images, but also in moving scenarios. A particularly striking example that exemplifies the accuracy required, and the smaller file sizes to speed up processing, is the combination of OTM data with rendered images in railway design that is able to show real-time drive-throughs, ensuring that train drivers can see critical signalling along the tracks.

Another prominent user of NEXTMap Britain datasets - Geo Information group, a primary data gatherer - uses them to add value to its Cities Revealed project, depicting cityscapes in 3D, and for creating carbon models combining thermal imagery with 3D terrain data to highlight hot-spots (literally) that require environmental attention. They also use the datasets for telecom network planning.

WHERE NEXT WITH NEXTMAP?

Intermap Technologies is using the experience gained in producing the NEXTMap Britain 2 dataset to expand the programme around the world. With the United Kingdom and Ireland, Germany, France, and Italy already

available, the entire NEXTMap Europe dataset will be commercially available by April of this year. NEXTMap USA, including Hawaii, will join it, and the company has already remapped large parts of South East Asia for the NEXTMap Asia programme.

The datasets are available from a number of resellers in the UK, and have been used to add value to dedicated applications, such as VFR terrain for England and Wales, and as an enhancement to Microsoft's Flight Simulator, showing real-world UK terrain used by commercial and private pilots worldwide.

INTERMAP TECHNOLOGIES

Intermap Technologies has about 800 people working for it. 500 of these are based either in Djakarta or Bangkok, currently working on the datasets for the rest of the globe! The datasets for NEXTMap Britain and the rest are based on its STAR technology, now in its 5th iteration. The decision to enhance its product with improved accuracy and smaller dataset sizes is a response to other organisations that are beginning to offer free data online.

Intermap believes that application developers, government bodies, environmental agencies and other users are dependent on the higher quality datasets that only Intermap is able to supply. For further information, contact Mark Stanley, Director of Sales, UK and Ireland, mstanley@intermap.com, or visit www.intermap.com

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