Article April/May 2000

The New Millennium Has Indeed Been Reached

Orthophotos in the U.K.!!

Having been involved personally with orthophotos for well over thirty years, it has always been a matter of disappointment and some perplexity to observe how little interest there has been in orthophotos in the U.K. By contrast, in most of Western Europe, there has been a long standing interest in and considerable use made of orthophotos and of the products derived from them. An obvious example is Sweden which started in 1937 with controlled mosaics and then, from 1966 onwards, utilized orthophotos as the basis for the main part of its national map coverage at 1:10,000 scale, with 1:20,000 scale used in the remote areas in the north of the country. Numerous other examples can be quoted - e.g. the German Grundkarte (Base Map) at 1:5,000 scale has also been produced in orthophoto form in several of the German states (Lander) since the late 1960s and early 1970s; and the 1:10,000 scale Orthophotoplan series was produced originally by the Aero Survey company for the whole of Belgium and has since been repeated by the Eurosense company.

By Professor Gordon Petrie

The U.K. Situation

However, in the U.K., the national mapping organisation, Ordnance Survey (OS), remained true to traditional line mapping at all scales. This is not to say that it did not carry out trials of orthophotos, e.g. for map revision purposes in the mid 1980s, but the method was never adopted for production. So the vast majority of British map users never encountered an orthophoto or an orthophotomap. Thus those commercial air survey companies such as BKS Surveys, Story & Partners and Clyde Surveys that invested in orthophoto technology in the 1970s found little outlet for the product in the U.K. Instead work for their equipment and facilities had to come largely from overseas contracts. Now however the new Millennium has been reached in more senses than the actual date. In this respect, dictionaries give the alternative meanings of millennium as being "one thousand years" and "a coming golden age". In the particular context of orthophotos in the U.K., the latter definition is quite appropriate. Almost unbelievably, a number of initiatives have been launched that have resulted in mapping agencies and companies in the U.K. making extensive use of orthophotos. Furthermore, U.K. users will at last have access to national orthophoto coverage at medium to large scales. Much of this change can be ascribed to the developments in digital photogrammetric and image processing software that have taken place over the last six or seven years. These have allowed orthophotos to be produced and become widely available in digital form, as well as in their traditional hard-copy form.

NRSC's Orthoview

It is convenient to start the story of these new developments with the launch of the Orthoview product by the NRSC company in November 1995. For this project, orthophotos were produced in digital form from 1:25,000 scale colour aerial photography using Autometric SoftPlotter digital photogrammetric workstations (DPWs). The scanned image data was ortho-rectified to fit the National Grid using OS 1:2,500 scale (Landline) digital map data for ground control and the digitized (Profile) contour data from the OS 1:10,000 scale map series - from which NRSC derived the required DEM. This OS data was supplied to NRSC under a special licence. The Orthoview digital orthophoto data was produced with a ground pixel size of 0.8m, either in the form of 5 x 5km tiles that matched the OS 1:10,000 scale map sheets or in the form of 1 x 1km mini-tiles. Certain areas - e.g. the West Midlands and parts of the East Midlands, South Wales and Northumbria - were covered in this way, mainly using archival photography. The product was sold to certain telecomms and military users as well as to some of the municipal and county authorities at which it was really aimed. However many other customers in the local authority and utilities sectors wanted the larger scale, better ground resolution (20 to 25cm) and greater detail that could be obtained from 1:10,000 scale aerial photography - which is widely used by these organisations. Thus, currently, the archived 1:25,000 scale photos are only converted to orthophoto form on specific request.

UK Perspectives

The direct follow-on from the Orthoview initiative has been UK Perspectives. Under this banner, NRSC has teamed up with another British air survey company, Simmons Aerofilms, in a joint venture to acquire new colour aerial photography of the whole of the U.K. at 1:10,000 scale. This is called the MAPS (Millennium Aerial Photographic Survey) Project. From the coverage produced by this Project, geo-referenced digital orthophotos will be produced for the whole country. A detailed account of this Project and of the procedures being used for its implementation has already been given by Greg Simmons in the January/ February 2000 issue of Geoinformatics, so there is no need to repeat it here. Thus far, the two companies have concentrated their efforts on England, which is by far the most populous part of Great Britain and offers the biggest market. 80,000 individual photographs will be needed to cover the whole of England. Each company in the partnership is responsible for the acquisition of specific blocks within the overall aerial photographic programme. However both partners can market and sell both sets of data. The data will also be available for on-line viewing and purchase over the Internet through TerraServer as well as being sold in hard copy form or on CD-ROM or DVD direct from UK Perspectives. As mentioned in Greg Simmons' article (see GeoInformatics, January/February issue, 2000), both companies have standardized on the LH Systems SOCET SET digital photogrammetric software for the aerial triangulation; the generation of the DEMs from the stereo-pairs; and the production of the digital orthophoto data. However while Simmons have also used DSW scanners from LH Systems, NRSC has utilized Z/I Imaging SCAI scanners for this part of its operations.

Millennium Mapping Company

A very similar but competitive project is also being undertaken by the Millennium Mapping Company (MMC). Again this aims to provide coloured aerial photographic coverage at 1:10,000 scale in digital form for the whole of the U.K. On demand, digital orthophotos will also be produced from this coverage. The MMC company was only formed in November 1998: its managing director is Tristram Cary, who formerly held directorial positions at NRSC. Whatever the similarities in terms of the aerial photographic scale and specification, this second project is being organised, managed and executed in a completely different way to that of the UK Perspectives partnership. In particular, a number of different specialist companies have been recruited and organised so that each is carrying out a particular stage in the operation with overall project management by MMC.

-Aerial Photography & Scanning

Thus a well known independent company, Cooper Aerial Surveys, based in South Yorkshire, is undertaking the flying and acquisition of the colour aerial photography using a fleet of twin-engined Aero Commander aircraft fitted with modern FMC-equipped cameras and using the Fugro Omnistar DGPS service for position determination. This is being done in conjunction with another company, Trackair of Marlow, Bucks, that carries out the flight planning and arranges the necessary air traffic and flying permissions. The exposed aerial photographic films are then passed to another company, Wildgoose, based in Coalville, Leicestershire, which carries out both the processing of the colour films and their scanning and conversion to digital form. The latter operation is carried out using three Linotype A3 high-resolution scanners that are currently operated on a 24 hour per day basis. The quality control of the processing and scanning is again carried out by Trackair. Wildgoose will also undertake the production of orthophotos from the coverage whenever this is required. For this work, it employs the PCI OrthoEngine AE and ER Mapper packages.

-Sales Network

Downstream from the main data acquisition and processing activities come the sales of the photographic products in both digital and hard copy form. This is carried out under the title of the Millennium Map. Again various partners have been recruited to undertake different aspects of this activity. In particular, a number of value-added re-sellers (VARs) who are already established in particular markets have been appointed to sell the products into these markets. They include Wildgoose in the education and library field and the Geoinformation Group - with its existing Cities Revealed and Counties Revealed archives and products - in the local authority sector. To complement these re-sellers, MMC is also building up a network of county-level franchisees, including retail outlets, to sell the Millennium Map products direct to the general public. In addition, an Internet-based browsing, sales and delivery system is being built by a specialist software firm, Softwright, while orders for hard copy enlargements, etc. will be executed by another firm, Rainbow Print, based in South Wales.

-Domesday Book

An unusual slant to the Millennium Map project is that it is being promoted heavily as a modern version of the Domesday Book. This famous document contains the first comprehensive survey and census of England carried out by William the Conqueror towards the end of the 11th Century. In 1986, to mark the 900th Anniversary of the Book, the Keeper of the Public Records in England arranged for the re-binding of the original copy of the Book, including the production of a high-quality facsimile copy of every page while this was being done. This work was carried out by Alecto, an associate company of MMC, which has now acquired the production and marketing rights to the facsimile edition of the Book. This is available in different forms - as a seven-volume full edition and as a three-volume edition for each individual county covered by the Book. In its promotional literature, MMC is emphasizing what it sees as the historical links and complementary nature of the Domesday Book and the new Millennium Map (which it also refers to as Domesday 2000!).

Ordnance Survey

In parallel with this high level of activity in the commercial mapping field, the Ordnance Survey (OS) has also moved into the field of digital orthophotos. In its case, currently it is using orthophotos produced from 1:7,000 scale aerial photography as the basis for much of its own in-house operation to carry out the revision of its 1:2,500 scale map series that covers the whole of the rural lowland parts of Great Britain in over 200,000 individual sheets. To this end, in 1996, it set up a production line based on the use of digital orthophotos generated by systems supplied by Intergraph that have been continually upgraded since then. Besides the older Unix-based system, this currently includes two new Z/I Imaging ScanServer systems together with Image Station Z DPWs that are used to carry out fully automatic aerial triangulation and DEM generation to supply orientation and elevation data for the ortho-rectification process. The orthophotos are then transferred to workstations running Laser-Scan's LITES-2 package on which the actual revision operation takes place with the existing digital map data overlaid on the digital orthophoto. The new features are then added by editors using manual head-up digitizing methods with purely monoscopic measurement of the revision detail being carried out on the monitor screens of these workstations. The orthophotos are mainly used in the flatter areas of the country. In the hillier areas, the OS still employs Leica SD2000 and Kern DSR analytical plotters for its revision work using feature extraction from stereo-models rather than orthophotos.

-Commercial Contractors

A substantial portion of this enormous rural map revision programme is also being undertaken by the commercial mapping sector under contract to the OS, which exercises a tough quality control on the operations of the various contractors. Interestingly, both Simmons and NRSC have a share in this work besides their UK Perspectives project. To this end, both companies have installed Laser-Scan workstations to replicate the OS procedure in their own labs - although the aerial triangulation and the generation of the orthophotos are carried out using SOCET SET (Simmons) and SoftPlotter (NRSC) DPWs, rather than the Z/I Imaging systems used by the OS. Other contractors such as WS Atkins of Pewsey, Wiltshire and Mason Land Surveys of Dunfermline, Scotland also use digital orthophotos as the source for their operations in the rural map revision programme. In the case of Mason's procedure, use is made of Z/I Imaging Image Station Z DPWs for aerial triangulation and orientation, with the PCI OrthoEngine AE package being used to generate the orthophotos. The monoplotting of the revision data is carried out on workstation screens using the I/RAS-C package from Z/I Imaging which allows vector digitizing to be carried out over the raster image background of the digital orthophoto.

-BKS Surveys

All of these contractors (NRSC, Simmons, Atkins, Mason) still utilize a number of analytical plotters to carry out the many other mapping projects that require feature extraction from stereo-pairs. However BKS Surveys of Coleraine, Northern Ireland have chosen to carry out their part of the OS map revision programme from stereo-pairs using Wild BC-2 analytical plotters and a single SoftPlotter DPW - even though the company does have an in-house orthophoto production capability utilizing a combination of the Autometric OrthoKork and ERDAS Imagine systems. Like the OS, BKS finds the use of a stereo-model advantageous in accuracy terms, especially in undulating or hilly terrain, rather than utilize a DEM derived from OS contours. But BKS has also carried out other projects involving the production of digital orthophotos, for example, in its provision of coverage of Guernsey and its smaller neighbouring islands in the Channel Islands.

Overseas Contracts

Several of the British aerial survey and mapping companies have also found further work producing digital orthophotos for overseas clients. Thus BKS has also undertaken orthophoto mapping, together with the production of vector line maps and a DEM, from 1:10,000 scale colour aerial photography for the whole of the island of Bermuda. This forms the basis for the land information system that is currently being implemented by the Bermuda government. Furthermore several UK companies have also been involved (through joint ventures with Greek partners) in the supply of digital orthophotos to form the basis of digital map data to be used in the large project concerned with the establishment of a national cadastre that is currently under way in Greece. For example, Survey & Development Services (SDS) of Bo'ness, Scotland have been generating digital orthophotos at 1:5,000 scale from 1:15,000 scale aerial photography for rural areas in Greece using VirtuoZo DPWs (for which SDS is also the European agent). However, for the urban areas, the generation of the vector line data at 1:1,000 scale is still being undertaken from 1:5,000 scale aerial photography using conventional stereo-plotting and feature extraction techniques on the VirtuoZo DPWs. SDS has also been generating orthophotos covering various municipalities in Belgium and the Netherlands on behalf of Aerodata International Surveys of Antwerp. This has involved the generation of the orthophotos from aerial photography at 1:6,000 and 1:12,000 scales flown by Aerodata. But the business is not just one way: thus, for example, Kampsax Geoplan in Copenhagen has produced both digital orthophotos and vector line plotting using analytical plotters for the OS rural map revision programme.

Conclusion

Besides all of these very large projects such as the Millennium Map, UK Perspectives and the OS rural map revision programmes, many other smaller projects producing or utilizing digital orthophotos have also been carried out in the U.K. over the last five or six years. This work has been undertaken on a contract basis by the commercial air survey companies. However, in the case of the Millennium Map and the UK Perspectives projects, the up-front costs of establishing national coverage are very high and it will be interesting to see if the uptake of the colour aerial photographs and orthophotos is sufficiently great to enable these costs to be fully recovered. This is especially the case if the companies intend to keep their archives fully up-to-date by re-flying those areas where rapid changes are taking place in the landscape. In this respect, these projects will face many of the same problems faced by the OS in its programme of continuously revising its 1:2,500 scale map series - which, at least in terms of coverage, scale and ground resolution, will still be a competitor to the two major orthophoto projects.

 

Professor G. Petrie (gpetrie@geog.gla.ac.uk), Department of Geography & Topographic Science, University of Glasgow, Glasgow, G12 8QQ,, Scotland, U.K.