Scott B Miller
Helava Associates, Inc.
10965 Via Frontera, San Diego, CA 92127, USA
A Stewart Walker
Leica AG
10965 Via Frontera, San Diego, CA 92127, USA
Scott Miller studied photogrammetry at the University of Wisconsin and Purdue University. He has been carrying out development work in digital photogrammetry since 1977, first with the Defense Mapping Agency and then with Helava Associates, Inc., for which he has been director of engineering since 1991.
Stewart Walker read geography and photogrammetry at the universities of Glasgow, New Brunswick and Bristol. After 10 years in an academic position at North East London Polytechnic (now the University of East London), he worked from 1987 to 1990 for the UK sales companies of Leicas predecessor firms, before moving to Switzerland in 1990 as Product Manager Digital Photogrammetry. As a result of Leicas close involvement with Helava, he relocated to the Helava offices in San Diego in 1994.
Economic Map
The most important product line of NLS is the Economic Map, which began in its present form in 1937 (Jonasson and Ottoson, 1974; Lindberg, 1988; Sporrong and Wennström, 1990). In the late 1920s attempts were made to create photo maps. Thus much detail previously surveyed in the field could be read and drawn directly from the aerial photographs. In 1931 tests were made using the aerial photographs as basic data (base material) when exploring the ground. As a result of all experimenting with aerial photographs a large programme was proposed for mapping at 1:10,000 scale based on photo maps. In 1937 the government ratified the programme and decided that during the next 30 years half of Sweden should be covered with the Economic Map. Since then both the maps and the techniques to produce them have changed and in 1978 the first map series of about 12,500 sheets of the Economic Map was completed. During this period there had also been revision of some of the earlier sheets. The photo maps have always played an important roll in the production of the Official Map Series and for the Economic Map also as an image layer. They were produced as controlled photo mosaics until 1967, when the use of orthophotos was introduced. These were first made on a Zeiss GZ1 ortho projector and from 1978 on a Wild Avioplan OR1.
Today the Economic Map, at 1:10,000 scale, has turned into a geographic database including almost all the features appearing on the printed map. To ensure rapid and accurate population of the database, numerous analytical plotters have been purchased and installed both at headquarters and in regional offices. The image layer is produced in a digital photogrammetric system and stored as digital orthophotos each covering 5 by 5 km corresponding to the map sheets of the Economic Map.
Today the Economic Map is actually printed at 1:20,000 and called the Yellow Map from the colour of its front cover. It is the basis and the most detailed map of the Official Map Series, which also include the topographic map called the Green Map at 1:50,000 scale, the road map called the Blue Map at 1:100,000 and the general Red Map at 1.250,000.
The Economic Map is used in administration, for example planning within agriculture and forestry. In late 1994 and early 1995 it played a very important role in the determination of the size of arable land for farmers in Sweden when applying for subsidy from the European Communities. In a very short time NLS produced the base material for the area calculations, most of it from archived originals of the Economic Map. The work attracted great attention and showed the capacity of NLS to set up effective production lines in a very short time.
Another application occurs when government authorities deal with questions concerning building permissions. The map is also the cadastral map and is able to record real properties and individual buildings with great accuracy. It is also extremely useful in providing an overview for the construction of roads, railways, electric power lines, etc.
Thus the Economic Map is a very special kind of map and GIS database with uniquely Swedish features such as the image layer, real estate boundaries and land register numbers, arable land and ancient monuments.
The tremendous developments in information technology and specially in GIS have increased the demand for digital land information (maps). NLS began, therefore, to convert graphical maps into digital information quite early. Early in 1970 computer controlled plotters were introduced and today the production line to collect and handle land information for the official map series is completely digital.
Both for the Red 1:250,000 scale and the Blue Map at 1:100,000 scale there exists digital information covering the whole of Sweden. Different themes of special interest, such as the Elevation Data Bank and the Place-Name Data Bank, have also been produced as databases covering the whole of Sweden.
The most requested information, however, comes from the Economic Map database (Ottoson, 1993), probably because the database is based on a very detailed standardised map covering almost the whole of Sweden and cyclically updated. A programme was set up in 1992 to convert the Economic Map into a geographic vector database in five years. This could only be done with big changes in its production. The work was concentrated on the database creation, the content was reduced and the production of the printed map had to be shut down after finishing the map sheets that had already been begun.
The production of the Economic Map as a geographic database is based on four different methods: complete revision, photomosaic revision, orthophoto revision and digitising of existing maps. The method chosen for each area is based on the condition of the available map material. For future revision of topographic information, only methods based on traditional and digital photogrammetry will be used to keep the collected data as accurate as possible. For the image layer, a decision has been made to produce digital orthophotos aiming at full coverage of Sweden by the end of 1998.
Through the efforts and good reputation of Swedesurvey, the overseas agency of NLS, many large projects have been won, which have placed additional pressures on NLS resources. To be able to manage them NLS has always needed leading edge technologies to make production more efficient and the resulting products of even better quality.
Decision for digital, decision criteria and bench-marking
The use of digital photogrammetry at NLS began in the 1980s with the use of an image processing system including a scanner with possibilities to scan with 25 µm resolution. Tests were made to produce digital orthophotos, with the idea of obviating problems in producing the Economic Map by expensively combining different original layers in the photo laboratory, as well as meeting other customer demands for othophotos. This system, Terragon, was then used for production of digital orthophotos from early 1990 until the procurement and installation of a completely new digital photogrammetric system in late 1994 and early 1995. The NLS Production division decided in March 1994 to do a preliminary study of digital photogrammetric systems. The study covered digital photogrammetry in general but with a special interest in the production capabilities for elevation data, digital orthophotos, aerial triangulation and also in mapping possibilities compared to analogue or analytical methods. There were also studies of scanners, not only those specially made for digital photogrammetry.
From this preliminary study and owing to some limitations in the old production line, NLS decided to look for as complete a digital photogrammetric system as possible. The main objective was the production of digital orthophotos. The system had to include a scanner with high precision, resolution and speed and provide an overall high performance in every practical aspect. The workstations should be based on open architectures and be built of up-to-date, high performance components. The system had to include all components that NLS deemed to be part of a complete digital photogrammetric system:
To be able to do a fair evaluation NLS decided to do bench-marking on the five suppliers. The bench-marks were made on a set of six images in two strips. The tests were supposed to take no longer than two days and to be at the locations most favourable for the suppliers, for all of them at their headquarters. The photos had known orientation data and include some PUGged points with known ground co-ordinates. Tests were made on scanning and all of the above mentioned parts in the complete system. The purpose of the tests was to compare the different systems with respect to their user-friendliness and productivity. For the latter, the times used for different productions steps were measured and user-friendliness was based on the number of keyboard inputs needed, the graphical user interface and the integration of and routes between different software modules. In late October the decision was made to purchase a complete digital photogrammetric system from Leica/Helava, consisting of a DSW200 Digital Scanning Workstations and four Digital Photogrammetric Workstations - a DPW670 monoscopic station and three DPW770 stereoscopic stations.
Installation and implementation
During the period before the delivery of the new system, people who were supposed to take part as operators took classes in both digital photogrammetry in general and in the use of the Unix operating system. Six of these operators usually work with photogrammetric tasks, for example as stereoplotter operators, and two of them, the ones who were to be responsible for the scanning, were very much involved in the production of digital orthophotos in the old, Terragon system.
The DSW200 was delivered in early December 1994 and the installation and calibration by personnel from Leica/Helava was made in two days. Thereafter the training by a Swedish speaking instructor of two scanner operators took for three days in the middle of December. The monoscopic workstation and one stereoscopic workstations were then delivered and installed in late December. The training on the software for the DPWs, SOCET SET® , was not done until mid January 1995, owing to Christmas holidays, but the system was up and running so tests could be made by some technicians. The scanner was also in use for scanning of images for test purposes and other customers. The DPW operators course took place at NLS during three weeks in January and February, again by a Swedish speaking instructor.
The new equipment was set up in two climate controlled rooms not far from each other. The systems were also placed very close to the traditional line for aerial triangulation which uses (cross-)PUGging techniques and analytical photogrammetric instruments from Zeiss. Block adjustment is done in PATB-RS, from output coordinate and orientation data could be directly imported to the Leica/Helava system for orientation of the digital images. For quality plots a Barco Graphics Map Publishing System is sited just a few rooms away. All this made the production line very tight, which helped the implementation of the new system. Thus the new system is part of the establishment of an integrated production line including the above components and based on the most recent developments in aerial photography and digital mapping technology (Figure 1). The line also includes the latest generation of aerial cameras from Leica, the RC30, and GPS based kinematic navigation and exposure control system called CAAP, Computer Assisted Aerial Photography, developed in-house.
Figure 1. The integrated production line at NLS.
The Leica /Helava system was installed with large discs at each workstation to prepare for large numbers of images to be scanned. The workstations and NLS mass storage system, the Hierarchical Storage Management HSM from Digital, were connected to each other via an FDDI net. With the help of FDDI it is possible to send images of 235 MB between the workstations in 1.5-2 minutes instead of the 4-6 minutes it takes on Ethernet. The use of FDDI is quite new for NLS so the network is still being tuned to make it possible to send data even faster.
Tests have also been made on the new automated triangulation software module in SOCET SET, HATS (Helava Automated Triangulation System), which we today consider to be approaching sufficient stability to be used in full production. The awareness of this software played an very important part in the procurement owing to the need to do a lot of aerial triangulation. NLS will enjoy even better conditions for production using HATS as the software is refined, better communication possibilities open over the FDDI net and, in view of the large amount of image data, even more disc capabilities are anticipated.
System support from the supplier has been most satisfactory to the customer. The local, Swedish speaking engineer has fixed several minor problems and there has been good e-mail response from Leica/Helava in San Diego. During some periods this spring they even had direct access to the NLS system via Internet. Today ftp servers with possibilities for anonymous login both at NLS and Leica/Helava are used for the exchange of data.
Applications
From late February 1995 until the present the system has been very much in use for production but all the time great efforts have been made to develop methods to use the system in the best way and make the production as effective as possible. The implementation of the new system was organised in a so called project organisation and not in the common production units that already existed. This made it possible to put people with different useful skills from different production units together. Today one of the three stereoscopic workstations is located in a production unit of traditional photogrammetry to be used in the production of small series of special products and introduced to some of the other stereo operators. The scanner and the rest of the DPWs still remain in the project organisation and are to be used for big jobs for which most of the production methods have been developed. More scanning operators are to be trained and the three technicians who have been doing the development of the methods and the customisation of the system is doing their best to support the operators and to find out new applications for the system. To learn the system even better, one of the technicians is going to take part in the DPW Software Developers Course which hopefully will lead us into an even more efficient use of the system, because it will be possible to use the software tool-kit to customise SOCET SET and integrate NLS applications.
The bulk of the work performed by the digital system so far has consisted of the image layer in the Economic Map database, Swedesurvey projects and special products. The production line for the image layer of the Economic Map is NLSs main line and was very influential in the procurement process. Today it is almost as efficient as possible. About 1000 black and white digital orthophotos have been produced: in Figure 2, one index square, for example 17E, equals 100 digital orthophotos each with one metre ground resolution covering map sheets of 5 km square tiles. They are produced from aerial photographs at negative scales of 1:60,000 or 1:30,000, acquired in a special programme set up by the government to cover Sweden with aerial photographs in a cyclic scheme. Diapositives are then produced in an in-house photo laboratory such that the photos within strips and homogeneous areas within an individual photo are as uniform as possible in a tonal characteristic sense. A representative diapositive from a group of photos is chosen to set up the scanner parameters. The parameters are then used to scan a group of photos to give a result with uniform illumination and tonal characteristics over a set of images. The pixel size of the DSW200 is set to 15 µm. Meticulous attention to operational details such as this, combined with scrupulous cleanliness of the scanner, the diapositives and the surrounding environment, has enabled demonstrably beautiful digital images to be obtained. Images are then moved from the disc at the DSW200 workstation or a special partition on the mass storage system via the FDDI net to be processed on the DPWs.
Figure 2. Orthophotos completed by 30 September 1995.
Elevation data is accessed directly in the file format used and the orientation data is read in as rotation matrices and camera positions to control the aerial photos to be used in the orthoproduction. The digital orthophotos are then archived on the mass storage as TIFF files together with their support files and thereafter plotted in the Barco plotter as black and white laser plots at 150 lines/inch.
There are large completed and current Swedesurvey projects in both Estonia and Latvia. These include the whole chain from planning, through aerial photography and aerial triangulation to the production of black and white digital orthophotos for digital delivery and output as laser plots. About 50% of the DTMs of the areas have been produced with automatic terrain extraction. (image matching techniques). Today about 400 out of 1000 1:2000 and 1:5000 scale orthophotos have been produced. There has also been some production of digital orthophotos for forestry companies. Some special products including digital orthophotos, elevation models for design and image map plots along road areas have been made for the National Road Administration.
There have also been tests made making very dense and accurate elevation data over city areas for telecommunication companies which are to be used for the calculation of where to place antennas for mobile telephone nets. For some of these tests orthophotos have been produced both in colour and colour infra red and plotted by a consulting bureau on a FIRE plotter as photo negatives 22 by 22 cm to be enlarged up to six times in the NLS photo laboratory to make orthophoto maps in any desired scale.
