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From CAD User AEC Magazine  Vol 22 No 7 - JULY/AUGUST 2009

AppsinCADD chooses OTM from NEXTMap for large scale terrain visualisations

Formed in 1986, AppsinCADD is a well established company known to many working within both GIS and CAD environments. The company provides a range of survey and terrain modelling tools under the brand name n4CE, catering for all aspects of data capture, processing, display and retrieval of Informatics for the engineer, designer, architect, surveyor or anyone working in the environment. Its products and services are platform independent, providing seamless interfaces to other complimentary products from AutoCAD, Bentley and ESRI.

So, of course, they know all about creating large scale digital terrain models, having had to put some of the earliest ones together for local planning authorities, so that they could create 3D visualisations and early 3D fly-throughs of the local landscape to impress their clients - the public! They are well acquainted with the sheer hard work that they had to put into preparing these by hand. This was about ten years ago, and in comparison with today's technology, they were working with pretty primitive equipment - slow computers, first generation graphics cards - and had to slice up the chunks of the early DTMs they had manually. It took them weeks to prepare their ground models!

So, when NEXTMap introduced the concept of OTM - Optimised TIN (Triangular Irregular Network) Models they were suitably impressed, realising that rather than spending all of that time converting the data into a usable format, here was a company that could supply the job already done, and in such a format that it opened up avenues for further development in their own line of work.

Together with Simon Gardiner, of G-VR, AppsinCADD explored the technology

further, particularly because of its suitability for the CAD market, and the way in which it will assist them in the development of usable large scale terrain models.

WHAT IS OTM?

There is nothing particularly exciting about the OTM concept. TINs are the GIS equivalent of surface meshes in CAD, a network of connected points that establish the layout of terrain in 3 dimensions. The TIN models derived from it will show, like any surface model in CAD, that where there is a concentration of physical activity - abrupt changes in height, prominent land features - there is also a greater concentration of nodes in the TIN.

The problem is that the improved surface scanning devices that NEXTMap uses provide more detailed point data clouds, which, converted into digital terrain models, produce very large data files. Quite apart from having to use pretty powerful computers to process these files, there is another problem that is

more relevant to CAD users of the data than GIS customers.

GIS terrain models are generally raster based 3D digital models. Users can, therefore, play around with these large data files, covering large areas of ground, because the software doesn't need to concern itself with triangles and polylines

-merely surfaces. CAD software, though, uses vector- based terrain models, derived from the same data source as those used in GIS applications. Loading data files of any decent size, therefore, and converting the raster data to vector data, brings most CAD systems to their knees. Large scale models covering, say, a 100 square kilometres, would cause serious performance degradation.

Which isn’t what it’s all about really, as one use for the software is the creation of real-life fly-throughs and visualisations, and any stuttering in its performance would suspend belief in the fly-through. (This isn't really real time, and you are not flying through the terrain a couple of feet above the ground!)

The answer lies in OTMs - Optimised TIN Models, developed by InterMap, who supply terrain data to software developers within the GIS and CAD industries - to integrate within their own applications. The data is derived from NEXTMaps bare-earth 5m postings - i.e. an accumulation of high resolution ground information from a number of sources, including radar scanning from low flying aircraft, and ground-based surveys.

OTMs use intelligent optimisation to shrink the size of these large data files and remove redundant information, using masks to preserve hard features, such as water edges. In practical terms, a DWG file covering an area of 1km square would, with 80% of detail retained, normally consist of 64,000 faces and be 2.5Mb in size. Optimised to just 5% it would show just 4,000 faces, and be no larger than 30Kb in size.

The optimisation process analyses the spread of heights, creating a full mesh, then optimises that mesh using an intelligent percentage value and sliding scale based on the spread of heights, working through the data files until they have all been reduced in size, but retaining relevant data. It then knits the meshes together. It can then insert the optimised meshes into the target CAD system, together with an image map. The end result is a highly realistic piece of 3D real estate!

Phil Langrishe, of Applications in CADD, who told me about the relevance of OTMs to the CAD market, explained the concept very clearly when he said that when you use OTMs, you don't pay more for less, but you pay more to do more with less! You don't get more information, you don't get higher resolution terrain models, but you do get to cover far greater ground in 3D with much smaller data files, allowing CAD and visualisation applications to address much larger datasets. In CAD Terms, that means that much larger DTMs can be considered as background for major construction projects - extensive road and rail projects, coastal improvement contracts and so on.

It's not only CAD that benefits either, as OTM generated DTMs can now be loaded onto smaller devices - handheld navigation devices, or even games players, providing users with improved visualisations in small scale - or even on the web, where excessive size literally brings browsing to a full stop.

There are other benefits for CAD users. OTMs are based on NextMAP Britain - a recognised data provider. • OTMs keep the shape of the original surface, but remove redundant triangles OTMs' are a tiled mosaic product. • Areas can be reprocessed, to reduce file sizes further. • Image referencing is included • OTMs are a CAD product as opposed perhaps to GIS Architects, Civil Engineers, Designers, Surveyors and Town Planners can work on much larger datasets, no additional hardware investment Fit for the same purpose as NMB • OTMs support, and are available to be used with AutoCAD, Microstation, 3D Studio Max, Cimena4D, SketchUp, etc.

APPLICATIONS IN CADD

Applications in CADD use OTM for special projects. - a range of terrain mapping and surveying tools including n4CE Survey, which processes and adjusts survey data using a spreadsheet editor, with bi-directional access to Total Stations, and XYZ extraction from CAD systems. N4CE Lite does much the same, but includes a fully interactive CAD Modelling environment - used to set out contours, sections and volumes, and can be configured with additional design options. Lite is extended with n4CE Professional, which includes river sections and higher quality presentation material, and n4CE Designer adds specialist applications for Geological Modelling, Mining, Railway Surveys, Alignment Design and much more. The company has also developed a couple of other applications, such as 4Site - an AutoCAD Plug-in for processing and data capture from Total Stations and GPS receivers. It allows surveyors and architects to take CAD systems and drawings out into the field, for setting out. Field Genius is Data Capture software from MicroSurvey in Canada with links to most popular Total Stations and GPS receivers, and Star*Net, which is an Internationally recognised Least Squares Network Variation of Coordinates, Traverse, Levelling and GPS Vectors adjustments program. A 10 station demo version is available for downloading.

www.NEXTMap.com
www.AppsinCADD.co.uk
www.g-vvr.co.uk

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