Perspectives of updating FUNDAMENTAL BASE OF GEOGRAFIC data ZABAGED/1

E. Muřický, P. Šidlichovský
Land Survey Office
ZABAGED section
Kostelní 42, Praha 7, Czech republic

INTRODUCTION

Fundamental database of geografic data ( ZABAGED/1 ) is being created since 1993. It should cover area of whole country at detail level of 1:10 000 base map. Czech Office for Surveying Mapping and Cadastre has the responsibility over the project, with Land Survey Office as an executive branch for developing and creating the database. All the seven regional Cadastral Offices are participating mainly by collection of data and their primary redaction, some of them also participate in developing parts of technology.

CHARAKTERISTICS OF ZABAGED/1

Source of original ZABAGED data are updated printing folders of Base Map 1:10 000 map sheets. Those are scanned at precize Konsberg scanner in 1016 dpi. Output raster files are then transformed into national coordinates - JTSK. Geocoded raster files are vectorized in Microstation environment, with IVEC for batch processing and GEOVEC for semiautomatic work. The result of the process is topologicaly clean topographical model. That means, though graphical element is presented only once, it may carry several meanings, e.g. road, landuse boundary and administrative boundary could be represented graphicaly by single line. The contours and positional data are stored in two separate files for map sheet. The files could be merged into one for map sheet, if required. There would be 60 graphical layers occupied in such a file, with 3 layers still in reserve.

The database is created and maintained in MGE / ORACLE environment, with MGDM for data acces and administration. MGE structure recognizes features and attributes. ZABAGED includes 8 categories of objects ( e.g. transport ), 103 object types ( feature classes - e.g. road, highway ) and 86 attributes ( road number ). ZABAGED vector files are available in DGN or DXF format. The vector files are temporarily supplemented by raster map ( CIT, resp. RLC format ), for build-up areas, which are not yet vectorized, with exception of water bodies and selected line elements.

CURRENT STAGE OF COMPLETION OF ZABAGED/1

There is 4573 map sheets for whole country. Filling of database closely follows new editions of Base Map sheets 1:10 000. Approximately 700 sheets is produced every year. By 31.5. 1998 2677 sheets are digitized, that is 59% of country area. It's necessary to realize though, that:

Build-up areas are not vectorized yet.

Contourlines are mostly just in 2D, withouth the assigned heights.

Vector data create so far just wire-model, with no attributes attached.

The vectorization should be finished by the end of year 2000. Though planned originaly after year 2000, vectorization of small to medium build-up areas should start in 1998 in Land Survey Office, depends on capacity available. The purpose is to complete vector drawing for respective map sheets. Large city areas will be contracted out to private sector, with attempts made to use existing digital data.

2D contours digitalization will be finished by the end of year 2000. 3D assignment is under production both by Survey Office and by other parties, who get 2D contours in exchange for the assigning of third dimension. About 400 sheets are available now. The proces has to continue faster in following years, due to dependency of ortofoto production for updating.

Filling of relational database tables will start probably by the beginning of next year, if the requested hardware arrives in time – till the end of june. It would be preferable, if sheets could be updated first and their (so far carthographic) position rectified, then attributed. It may happen, two attributing runs will be necessary, if all attributes are not available. That may be the case of data from some external providers.

UPDATING OF ZABAGED/1

The purpose of updating is both to improve geometry and topological relations and to implement changes detected in terrain. Result should be real topographic model, with details at level of 1:10 000 base map.

Equipment

Technology of updating should benefit as much as possible from digital and analytical photogrammetric equipment and topographical field survey. For this purpose the COSMC sector was equiped by :

Unfortunately this technology is dislocated in seven places - on regional cadastral offices and Land Survey Office. The largest concentration of technology is in Cadastral Office in Pardubice, where scanner and single DPW is located. Such distribution of technology is disadvantegous from practical and economical points of view in comparison to single centre. Some problems in data transfers could be anticipated.

Ortofoto production

Most of work on improving of position data should be done over orthophotos, because usual workstations or PCs are enough for the work.

Parameters for aerial photography were set based on former technology for classical maps. Flight should be done in early summer or late autumn, so that minimum vegetation cover is present. Preferably in noon hours. Scale of photographs will be about 1: 25 000, camera focal lenght 150 mm, 60% overlap in flight direction, 35% overlap between rows. The flight axis has the east- west orientation and should correspond to line connecting map sheet centres as much as possible. The aim is to have one picture over centre of map sheet, the following one on the border and so on. In this way every map sheet will be covered by two stereomodels or single image, though all images will be used for ortho production.

Scanning of photographs will be done by SCAI scanner in Pardubice, it's capacity is quite sufficient for whole production. Available pixel sizes are 7, 14, 21, 28, 56, 112 and 224 um. Initialy the 21 m m will be used, believed to be balanced between size and interpretability, with possible changes in future.

Naturaly signalized ground control points will be used, selection of points will be marked on paper copies of aerial photographs. Points will be measured by GPS. The possibility of fixed network of GCP for whole country has yet to be considered.

Aerotriangulation ( internal, relative, absolute orientation ) will be computed and measured on SD 3000 in Liberec, the station will need just about one third of it's capacity for the task.

The 3D contours could easily be used for orthophoto production. Of course after changes are implemented and after some editing in areas not well described by contours - narrow valleys, which tend to be cut in imported data. At some areas new height data has to be created - unwooded hills, mining areas etc. Unfortunately only DPW stations are equiped by 3D superimposition, where editing of elevation model is much easier.

The ortofoto production will be provided by DPW's 770, with orientation data from ORIMA and elevation data from updated ZABAGED contours. If, in the future DPW sttions get too busy with other tasks - editing of DEM for example, the orthophoto production will have to be shifted to some universal PC or workstation, equiped additionaly with necessary software.

Revision and updating of geometry

Updating and rectification of geometry of ZABAGED data will be done over orthophotos. Because accuracy of orthophoto is in close relation to accuracy od used DEM, it's not convenient to struggle to move all vectors exactly into their respective place on image. Some tolerance ill have to be established, maybe different for different classes of elements. So far three meters for buildings and roads appears to be realistic value. But some experiments still have to be done in that area. Build-up areas should be updated in stereovision on SDs, or existing large scale data could be utilised, where available.

Field survey

Field survey will have two main tasks. First one concerns geometry: Providing coordinates of elements not distinguishable on images where simple GPS would be valuable, though still not available for the task., highlighting changed areas, second one concerns the collection of variable attributes data - functionality of buildings, types of areals, names of water streams etc. Copies of sheets with redactional preparation for vectorization should serve as primary basis, where latest known situation is presented. There changes should be marked and additional information added. Also, as part of data preparation for the actualization process, the cadastral boundaries should be checked and differences between water-management map and ZABAGED solved.

Timetable of updating

In year 1998 only the experimental production could proceed. The technology should be tested and improved and also newly received photogrametric equipment should get into operational use.

In 1999 there should already work small updating process with reduced capacity, because filling of database will still go on, swallowing most of resources available. Assigning of attributes should also start in year 1999, so it would be preferable, if geometricaly corrected sheets could be attributed. It would spare some work and a lot of database managenent problems. First updating cycle should be finished by the end of 2005, when there wuold be complete topographical database, corresponding in detail to former 1: 10 000 base maps, with accuracy of about 5 m in position. New base maps should be also produced out of this database.

It's expected the database will be complexly updated once every 5 year, depending on new aerial photography, though some elements could be maintained in shorter periods, maybe even "semi"-continuously.

Conclusion

Data of ZABAGED/1 are already , even though uncomplete and not covering whole country, asked for a lot. The detail level is quite sufficient for most applications, while the scale ensures, that though data are derived from carthographic source, the generalization is almost none. Even more utilization could be expected, when whole country is covered, by the year 2000, and when the relational database is completed. The database should form a backbone of state information system, whatever way it's development takes.

REFERENCES

  1. Uhlír J. : Zabaged - present state and perspective of creation and utilization. Geomatica 98, Materials of adjoining conference "Land surveying and cadastre as information systems" (in czech language), Prague 1998