DEVELOPING A NEW GEOGRAPHICAL OBJECT DATABASE. EXPERIENCES FROM IDEA TO DELIVERING DATASETS TOP10NL

Transcription

1 DEVELOPING A NEW GEOGRAPHICAL OBJECT DATABASE. EXPERIENCES FROM IDEA TO DELIVERING DATASETS TOP10NL NICO J. BAKKER Topografische Dienst Kadaster Bendienplein SM Emmen, The Netherlands nbakker@tdkadaster.nl ABSTRACT TOP10NL is the new object database at the scale 1:10,000 of the Dutch Topografische Dienst Kadaster. For developing this database the last four years different projects has been started to realise a whole new dataset and production environment. We started with consulting the users of the current CAD-like database to establish their wishes. Together with our user organisation and three universities the new data model was developed and test datasets were produced and spread out to the (potential) users. Important activities are the conversion of the current CAD data to object data and the development of a new production process. Next is the visualisation of the object data.. This paper reviews the different phases in the development of the new database and looks forward to the new possibilities TOP10NL will offer to the users. INTRODUCTION The Dutch National Mapping Agency, the Topografische Dienst Kadaster (TDKadaster), started in 2001 a study into a new database structure for its topographical vector files. Since the beginning of the 80s of the previous century, TDKadaster produced topographical maps and vector files using CAD software, in our case Microstation. The microstation dgn files are provided to a lot of users, particularly local, provincial and governmental organisations, as well as water boards and utilities. Moreover the vector files are used for the production of raster files and paper maps. Therefore we use MapPublisher software from Intergraph since The vector files and derived maps have been available since 1997 for the whole country and are revised in a 4-year cycle. In the middle of the nineties applications in Geographical Information Systems became more and more common practice. This made other demands to geographical datasets. GIS software developed further and the users wanted to execute more complex analyses with the geographical data. In the Netherlands also the demand to a national core dataset was growing. This was reason for TDKadaster in 2001 to start a project to examine the renewal of the database. This paper gives an overview of the development of the data model and the data base and the activities which are related. MARKET RESEARCH To form a notion of the wishes of the customers a rough market research was started. An independent party was involved, a research institute, linked to the Wageningen University. The research institute had made a lot of applications for users and was familiar with the needs of the users. Based on these results a new data model was developed in collaboration with the Technical University of Delft and the ITC in Enschede. Some test datasets were produced according the OGC standard in GML 2.0 and also as shape file. For a broader consultation of the customers a demo CD- ROM was produced and distributed under the users and other who were interested, together with a questionnaire. Based on the answers the data model was revised. CHARACTERISTICS OF TOP10NL Designing the data-model and its structure the following user requirements were taken into account: - Object-oriented data-model with unique ID s, - Structured attributes with the possibility to add new attributes, - Based on international standards (ISO, OGC), - Change-only data instead of complete update delivery,

2 - Availability of object life cycle information, - Meta data on object level, - Distinction between Digital Landscape Model and Digital Cartographic Model, - Seamless database, - Integration TOP10vector (roads as polygon) and TOP10roads (roads as centre-line), - Prepared for automatic generalisation and scale less database, - Linkage with user data-models (e.g. environment, water) and user datasets. The features, already stored in the current database were rearranged according the new defined object types. See figure 1. Geo objects Objecttypes - Road segment - Railroad segment - Water segment - Terrain - Building - Specific terrain element/ construction - Administrative area - Geographic area - Functional area Figure 1: Object types of TOP10NL In the Netherlands recently the national standard for modelling geographical data is revised. This standard is meant for reference data as well as thematic data. The old model dates from 1996, and was not in accordance with the international standards from ISO and OGC. In 2004/2005 these standard was reconsidered under the name Basismodel Geo-Informatie (NEN3610 version 2) (Base model for Geo Information). TOP10NL has been harmonised with this new standard. Corresponding object classes are described in accordance with NEN3610 version 2 standard. The specific Figure 2: Detail of the UML model TOP10NL

3 contents which specifies TOP10NL is modelled separately within the standard structure of NEN3610 v.2. This contributes to the fact that in the future the exchange with other geo-datasets must be flexible. The data model is modelled in UML (Unified Modelling Language). A detail of the data model in UML is shown in figure 2. After the determination of the TOP10NL data model we built a new database structure. For storing the geo-objects an entirely new database structure has to be set up. For the database has been chosen for Oracle 9i. On the basis of conceptual data model the technical implementation of the database was developed. CONVERSION OF TOP10VECTOR TO TOP10NL An important project concerns the conversion of the current TOP10vector data to the new object-oriented data structure in accordance with the data model of TOP10NL. The TOP10vector dgn-files are built with encoded points and line features. In many cases the lines are coded with multi coding. A line feature in TOP10vector can be a roadside, as well as a watercourse and also a line of trees, specially when these features are parallel line elements in reality. Moreover the lines are provided with left and right for coding for coding adjacent areas. Additionally, within closed polygons centrepoints are digitised which have the code of the land use of that area. Next to TOP10vector with coded polygons for road elements another dataset is available with centre-lines of the roads (TOP10roads). Features from both datasets will be included in the TOP10NL objects. The new dataset TOP10NL is object-oriented, this means that all the (geo-)objects have an unique ID and have descriptive, temporal and meta information as attributes of the objects. The conversion of TOP10vector elements to TOP10NL means a analysing of the CAD-features in loose parts and these are put together to objects according to the data model. The conversion process is carried out in different steps. The challenge was to perform the conversion process as much automatically as possible. The first phase concerns producing road crossing objects. This is done for approx. 80% automatically. For that purpose special software has been developed. Complex situations are carried out manually by cartographers. Then so-called pre-objects are composed. For this extremely complex process a conversion diagram has been built within the software FME (Feature Manipulating Engine) of SAFE software. This conversion composes objects from separate line elements which were analysed from the CAD files. In this process also as many attributes as possible are filled automatically from the original dgn file. Also text features, which are stored as loose text elements in the CAD files are linked as attributes to the objects they belong to. However not all the information can be joined directly to the objects. After automatic conversion follows a final process in which the quality control plays an important role. In the conversion process as well as in the filled database several checks are carried out on correct and complete conversion and the consistency of the files. This is possible by means of constraints, which are defined in the database environment. In the final step of the conversion the cartographer adds and improves manually the object attributes. OBJECT EDITOR To produce object-oriented TOP10NL data and to update these data, we examined existing production software that should be able to edit data in the new data structure. We decided to develop a new production process for production and updating the geometry and attributes of the objects. For the selection of off-the-shelf software a benchmark was carried out between five software vendors. Finally for this part of the production ArcGIS 9 of ESRI has been chosen. Figure 3: Example old and new interface However for an efficient production workflow and connection to the existing production processes, much additional software has been developed. Also the standard interface has been considerably adapted to the wishes of the

4 topographers. An important pre-condition was also that the topographers could work both offline and online with same the functionality. A part of the work is done at the office, when a connection to the central database is possible, another part in the field. For the production of TOP10NL a new interface has been designed (see figure 3). An important question is how to deal with object updates, the lifecycles of objects: when a new object comes into existence, when it is considered as a modified object with conservation of the object ID and when an object ends to exist (but remains as historical object in the database). We talk about new objects, disappeared objects, aggregation and splitting of objects, geometrical modifications and attribute modifications. For that purpose a number rules are established which ensure the allocation of new object-id's, and for conservation of the ID's with a new version date. This allocation should be done automatically, without intervention of the topographer/operator. The updates of objects takes place in a copy of (a part of) the central database, the work set. For update of the work in progress a part of the Core database is copied to a work set. Objects get temporal object-id s. After the update activities the work set is written back to the core, where the modified objects are compared with the existing objects in the core. By means of the so-called life-cycle protocol new object-id's or new version dates of objects are automatically allocated to existing objects. See figure 4. Produce orthophotos Delivery Terrain Reconnaiss ance Water boards Process External Sources Managing tasks Planning Control Workset Update & lifecycle GBKN buildings Process External Data rules Manage Model TOP10NL Core delivery TOP10NL GML SHAPE Figure 4: Workflow TOP10NL The architecture of the new production environment is shown in figure 5. Figure 5: New architecture of TOP10NL production For efficient updating of the objects special functionality is developed in ArcGIS 9. A function called punching helps to resolve creating of new objects and the splitting and merging of existing objects when an update activity takes place.

5 In figure 6 the successive steps are shown. Figure 6a shows the existing objects and the contours of a new road (in green). Figure 6b shows the polygons of the new road, created by one button push, above the existing terrain polygons. In figure 6c the punch functionality is running and creates new objects and splits the underlying objects in smaller ones. Figure 6d shows the new situation. Figure 6a Figure 6b Figure 6c Figure 6d LIFECYCLE OF OBJECTS What happens with a modified object depends on the size of modification. At 'small' modifications an object gets a new version date. At 'large' modifications the original object terminates and a new object is erected with a new TOP10_ID and a starting date. Then the original object is considered as disappeared, and gets an end date. If a modification is 'small' or 'large', is subjective. For that reason rules have been defined, to judge to what extent object modifications leads up to a new version date or new TOP10_ID. When there is a modification, it can be a modification of the object type, a change of attributes or the geometry has changed. Depending on the kind of modification certain rules are applied. Small changes of the geometry won t cause a change of object ID. Using a certain buffering around the original object, and when the changes are within the buffer, the object keeps the same object-id and alone the version date is changed. When an attribute has changed, in the most cases only the version date is changed. - Aggregation of objects For this case a rule is defined to prevent that there can be more TOP10_ID's allocated to one object and is applied when objects are joined together. When the size of the new object amounts less than 200% of the size of one of the original objects, then it gets the existing TOP10_ID with a new version date. When the size of a new object amounts 200% or more, compared to the original object, then it does not get the original TOP10_ID (see figure 7)

6 Figure 7: Application of the aggregation rule. The size of the new object is more than 200% of the size of the original object with TOP10_ID This TOP10_ID does not get the riginal ID. When the size however is less than 200% of the size of the original object with TOP10_ID 0012, this TOP10_ID is kept. - Splitting rule This rule prevents that several new objects get the same TOP10_ID by splitting up an object. When the size of a new object is more than 50% of the size of the original object, then it obtains the same TOP10_ID with a new version date. The other new erected objects obtain a new TOP10_ID (see figure 8) Figure 8: Application of the splitting rule. The area of the small new object is less than 50% of the area of the original object. It doesn t take over the TOP10_ID but gets a new OP10_ID. The area of the large new object is more than 50% of the surface of original object and takes over the TOP10_ID Other examples The object characteristic metalling of a road changed from ' unpaved ' in ' paved or metalled '. In this situation the object only gets a new version date. See figure Figure 9: Attribute change of river The boundaries of to areas are changed: a terrain area becomes larger, at the cost of another terrain area. The light coloured area takes, according to the aggregation rule, the TOP10_ID of the original area (0491). The other area takes the TOP10_ID of the original dark coloured area (0492). See figure Figure 10: Changing area A watercourse gets another course. The new water course overlaps enough with the original watercourse, that it, according to the overlap rule takes over the TOP10_ID. See figure 11. Figure THE EXCHANGE STANDARD GML From the start of the research to the new database, also the existing exchange formats of data played an important role in the considerations. The current TOP10vector files are provided to the customers in five different exchange formats, depending on the software used by the customers. This means on one hand that a lot of time is put in the conversion of vector files to the different formats, on the other hand with some conversions a part of the data were lost.

7 Also extra memory space is needed to store all the different data formats. In 2002, the first version of GML came available, developed by the open GIS consortium (OGC). For the production of the first prototypes we waited to the availability of GML 2.0, because this version should be backwards compatible. Although most large GIS software vendors are member of the OGC, it was not yet clear or all of them effectively supported the GML format. To this purpose the developers of the Technical University of Delft, in cooperation with TDKadaster organised three GML relays the last years. At these relays several software suppliers were invited to test the TOP10NL test data set, trying to prove that the software was able to read and write the GML data. After a little change in the data the dataset was written in GML again and handed over to the next participant to read it with their software. The first GML relay in 2002 provided only a limited result. Only 2 of the 7 participants were able to read the data. In November 2004 the third relay took place. Five software suppliers had submitted an application. They were all able to read in the data. However reading in by other participants after an update, caused still problems in some cases. In the meanwhile a new version GML has become available (GML 3.1). The primary delivery of TOP10NL data by TDKadaster will be in GML. At the end of 2005 the last final GML relay will take place, preceding to the definite supply of TOP10NL in VISUALISATION One of the advantages of the new structure is that the user is able to visualise the TOP10NL data according to their own needs. Nowadays a limited number of visualisations have been defined for raster data and paper maps. Creating other visualisations of the data are rather complicated in the used software. With the new structure of the data and the use of modern GIS software a lot of other customer specified presentations of the data are possible. The object types and a combination of attribute values can be used as parameter for special visualisation purposes. TDKadaster will define a limited numbers of visualisations for paper maps and web use. COMMUNICATION The new product TOP10NL will be released in For the introduction several activities are undertaken. Two projects are Early Adaptors and Application Developers. In the early adaptors project, preceding the market introduction, a number of end-users are invited to test a dataset in their own production environment. One of the tests will be the possibility to read and write the GML data in their own software. Another question is the way they can use the new data structure of TOP10NL compared with the existing TOP10vector dgn files. For the early adaptors program users from several user communities are selected, as municipalities, provinces and national governmental institutes. A second introduction activity aims at GIS software companies who develop applications for end-users. In many end-applications the geographical data are only one part of a lot of datasets combined with specific functionality. It s important to communicate with the applications developers that they have to integrate object-oriented data in stead of CAD files, so they can change there applications in time. Other manners of communication to inform the users are of course publications, leaflets, presentations, newsletters, website, workshops and conferences. CONCLUSIONS Conversion of the topographical CAD files to GIS data as objects takes a long time. The most important steps from whole conversion process are (see figure 12): - market research, inventory of the customer wishes, and research to the new technical possibilities, both in the field of hardware, and sophisticated software, - development of new object oriented data model, taking into account national and international standards, - Designing, building and arranging a new database for storing the data, - Conversion of the existing data to the new data structure, - Establish a new production workflow which optimally supports the new date structure, including education of the software developers, administrators and topographers, - Communication of the new product to the market, the users by means of publications, presentations, newsletters, test data sets and pilots.

8 Figure 12: Time sequence of TOP10NL development TDKadaster will start the delivery of the new TOP10NL data in ###