Constraints in geo-information models and their implementations in systems

1. Constraints in geo-information models and their implementations in systems Peter van Oosterom GIS technology, OTB

2. Contents • Introduction • Constraints in a landscape design VR system • Constraints in a cadastral data set (topology) • Constraints in a topographic base data set • Constraints in web feature service transactions • Classification of constraints • Support for constraints • Conclusions and further research

3. IntroductionGeo-information models • OMG’s Model Driven Architecture (MDA): the model forms the foundation for further system development • The data aspect of the model is often described in a UML class diagram (Unified Modeling Language), which defines for a class: • Attributes (names and types) • Methods • Associations (generalization, aggregation) • However, often constraints are ignored

5. IntroductionConstraints • Constraints are conditions, which always have to be fulfilled by the user and/or by the data processing operators of the system • Constraints can be related to properties of the object itself and/or to relationships between the objects Example:Tree must never stand in the water

6. Introduction • More attention for constraints needed as they add meaning/semantics to the model • Constraints enable further consistency checking • Constraints should be explicitly modeled, specified once and used throughout system: • Create/edit objects (in GIS/CAD editor) • Storage/manage objects (in geo-DBMS) • Exchange objects (in communication, XML)

7. Contents • Introduction • Constraints in a landscape design VR system • Constraints in a cadastral data set (topology) • Constraints in a topographic base data set • Constraints in web feature service transactions • Classification of constraints • Support for constraints • Conclusions and further research

8. The SALIX-2 system • Landscape architectural design • Interactive planting trees, bushes • Growing simulation Constraints to improve the interactivity! Originally developed by Wageningen University Adding constraints: MSc-thesis project of Jildou Louwsma

9. The SALIX-2 system: User Interface

10. Three classes objects: trees, bushes and ground surface Trees and bushes: CorAve, CorMAs, FraxExc, QueRob, RosCAn Ground surface: water, paving, grass and bridge. UML class diagram for SALIX-2

13. Constraints in SALIX-2 (1) • Direction:A bush always has to placed south of a tree • Topology: Bushes always have to be disjoint or meet water; A bush always has to meet or be disjoint paved areas (also thematic constraint) • Metric: Trees always have to be positioned > 1 meter from paving • Temporal: An oak always grows for 70 years • Quantity: There must always be at least 10 trees on the specified ground surface

14. Constraints in SALIX-2 (2) • Thematic: A bush always has to meet or be disjoint paved areas (also topological constraint) • Complex: The distance between trees inside water always is > 8 m AND the distance between the tree and the edge of the water always has to be < 0,5 meter AND the species must be a salix;Trees of type 1 always have to be placed west of trees of type 2 AND the distance between trees of type 1 and trees of type 2 must always be 7 meters (pattern)

15. All SALIX-2 constraints specified as assertions (SQL92 standard) CREATE ASSERTION <assertion_name> CHECK <constraint_body> Bushes never lie inside water: create assertion constraint_1 check (not exists ( select * from prcv_treesrd_point t, prcv_gvkrd_poly g where t.treetype in (‘CorAve’, ‘CorMas’, ‘RosCan’) AND g.descript = ‘water’ AND sdo_relate (g.geom., t.geom., ‘mask=inside, querytype=window’) =’TRUE’)) However, not available in any mainstream DBMS

16. SALIX-2 constraints hand-coded in Oracle Triggers/Procedures CREATE OR REPLACE TRIGGER ast_salix AFTER INSERT ON prcv_treesrd_point BEGIN -- constraint 1: a bush must never be placed inside water the existing -- table with all objects has no bushes inside the water, so only -- after each update or insert a check has to take place if -- the new location of a bush is inside water. This can be -- an after statement trigger. IF pck_salix.treetype_io IN ('CorMas', 'RosCan', 'CorAve') THEN -- the object is a bush, so all constraints concerning -- bushes must be run. DBMS_OUTPUT.PUT_LINE('the involved object is a bush'); pck_salix.pr_topology_c1; ELSE raise_application_error(-20099,'the object is a tree, no constraints have to be checked.'); END IF; END;

17. Triggers/Procedures in SALIX-2 PROCEDURE pr_topology_c1 IS description varchar2(15); xrd_io number; yrd_io number; bush_in_water EXCEPTION; BEGIN SELECT g.descript, t.geom.sdo_point.x, t.geom.sdo_point.y INTO description, xrd_io, yrd_io FROM prcv_gvkrd_poly g, prcv_treesrd_point t WHERE t.treeid = pck_salix.treeid_io AND sdo_relate(g.geom, t.geom, 'mask=anyinteract, querytype=window') ='TRUE' GROUP BY g.descript, t.geom.sdo_point.x, t.geom.sdo_point.y; IF description = 'water' THEN raise bush_in_water; ELSE DBMS_OUTPUT.PUT_LINE('1: the bush is not placed in water'); END IF; EXCEPTION WHEN bush_in_water THEN raise_application_error (-20001, '1: The bush (x='||to_char(xrd_io)||', y='||to_char(yrd_io)||') is placed inside water, but a bush may never be placed in water. Place the bush on another location.') END pr_topology_cl;

18. Never in Water (example)

19. Some lessons, VR landscape design • Constraints occurs at different places: VR user interface and data storage • When designing: immediate feedback to user is important • DBMS support of assertions is non existent! • Simulation adds an other ‘dimension’ to constraints: when creating an initial plantation layout everything may be correct, but after 5 years of simulated growth there may be conflicts; trees get too close

20. Contents • Introduction • Constraints in a landscape design VR system • Constraints in a cadastral data set (topology) • Constraints in a topographic base data set • Constraints in web feature service transactions • Classification of constraints • Support for constraints • Conclusions and further research

21. Netherlands Cadastral map (1:1000) • Based on winged edge topology stored in DBMS • Redundancy in references; e.g. both object_id left/right and parcel_number left/right • Considered as a topological very clean data set • Hard coded topology checks build in editor and check-in software; at DBMS server sided, but not in DBMS • Data set with history 1997-2004: • Boundaries/polylines: total 67.000.000 (22.000.000) • Parcels/faces: total 28.000.000 (7.000.000 actual)

22. ll_line_id l_obj_id lr_line_id fl_line_id r_obj_id fr_line_id Topology references

23. Spatial types, topology references(boundary: polyline, or circular arc)

24. Some, of the about 50, constraints (‘create assertion’ part skipped) • find closed ‘arcs’ (circles not allowed, not l/r side)SELECT object_id, numpoints(shape), anypoint(shape, 1), anypoint(shape, 2), anypoint(shape, 3)FROM xfio_boundary WHEREnumpoints(shape)=3 and interp_cd=3 and tmax = 0 and ogroup = 6 and(anypoint(shape, 1) = anypoint(shape, 3)); • find straight ‘arcs’ • parcel reference point not in bboxSELECT object_id from lki_parcel WHERE inside(location, geo_bbox) != 1;

25. Enlarged (cell=5mm) Closed ‘circular arc’ & geometric 1 mm gap

26. Enlarged (cell=5m) Straight line coded as circular arc

27. Topology reference exist • Boundary: left or right parcel obj_id does not existSELECT l_obj_idFROM lki_boundaryWHERE l_obj_id not in (select object_id from lki_parcel); • Boundary-boundary reference does not existSELECT object_id, fl_line_id FROM lki_boundary WHERE abs(fl_line_id) not in (select object_id from lki_boundary) • Parcel: outer boundary reference does not existSELECT object_id, line_id1 FROM lki_parcelWHERE abs(line_id1) not in (select object_id from lki_boundary); • Parcel: island boundary reference does not exist or wrong number of island references, l_num-1

28. Island reference is missing

29. Topology reference correct • Two consecutive boundaries must have same parcels at the side; 8 combinationsSELECT s.object_id, s.fl_line_idFROM xfio_boundary s, xfio_boundary rWHERE s.fl_line_id > 0 and s.fl_line_id=r.object_id ands.tmax=0 and s.ogroup=6 and r.tmax=0 and r.ogroup=6 ands.r_obj_id <> r.l_obj_id; • End point of one boundary is start of next; 8 combSELECT s.object_id, s.fl_line_idFROM xfio_boundary s, xfio_boundary rWHERE s.fl_line_id > 0 and s.fl_line_id=r.object_id ands.tmax=0 and s.ogroup=6 and r.tmax=0 and r.ogroup=6 and(anypoint(s.shape, 1) <> anypoint(r.shape, 1)); • Check if island boundary has parcel at the right side, check if first coordinate of island is within bbox parcel

30. Parcel refers to wrong island boundary

31. More consistency checks… • Boundary  Parcel references not consistentSELECT s.object_id, s.line_id1FROM xfio_parcel s, xfio_boundary rWHERE s.line_id1 > 0 and s.line_id1=r.object_id and s.tmax=0 and s.ogroup=46 and r.tmax=0 and r.ogroup=6 and(s.object_id <> r.r_obj_id); • Redundant double references, via object_id and parcel_number, not consistent • Geometric/survey and admin/right/owners side of parcel not consistentSELECT count(*),municip FROM mo_objectWHERE pp_i_ltr='G' and x_akr_objectnummer not in (select x_akr_objectnummer from lki_parcel)GROUP BY municip;

32. Some lessons, cadastral data • Never trust on front-end and/or middle ware alone for consistency checking  check within DBMS • Even if the errors may not be noticed in the production environment, they may be harmful in the environments of others; e.g. straight ‘circular arcs’ • Not yet all aspects checked; e.g. • time intervals of two consecutive versions of an object should touch • the complete domain is covered with parcels • at one moment in time no (straight line or circular arc) boundary may cross, only touch at end points is allowed

33. Contents • Introduction • Constraints in a landscape design VR system • Constraints in a cadastral data set (topology) • Constraints in a topographic base data set • Constraints in web feature service transactions • Classification of constraints • Support for constraints • Conclusions and further research

34. Designed with constraints included in one single source model • New topographic product TOP10NL (from 1 jan 2006) • New production system: from files to DBMS • New exchange format: GML3-based and NEN3610-v2 • Initially constraints designed for validating conversion • However, same constraints will be used during future production editing • Constraints specified in one source in own XML-format (by Vertis and Topographic Service)

35. Types of constraints (as defined by Vertis and Topographic Service) • Single entity, single attribute (thematic)0 < road.num_lanes <= 10 • Single entity, multiple attributes (thematic) road.A-number <> ‘’ then road.type=‘highway’ • Geometry (besides some general rules minimum length of line and minimum size of area)road.width_class ‘<2m’ then geometry is line else area • Topology (several subtypes: covering_without_gaps, no_overlap, coincide, …)road, water and terrain may not overlap at same height • Relationshipevery feature must have at least 1 specified source

36. XML encoding of domains, ex. 1range type (width of water) <Domein> <Naam>dWaterBreedte</Naam> <Registreren>J</Registreren> <Beschrijving>Breedte voor Waterdeel</Beschrijving> <Type>Range</Type> <DataType>int</DataType> <CodedValueData/> <RangeData> <Minimum>1</Minimum> <Maximum>500</Maximum> <Default>6</Default> </RangeData> <SplitRegel>Duplicate</SplitRegel> <MergeRegel>DefaultValue</MergeRegel> </Domein>

37. XML encoding of domains, ex. 2enumeration type (type of railroad) <Domein> <Naam>dSpoorTypering</Naam> <Registreren>J</Registreren> <Beschrijving>Typeringen voor Spoorbaandeel</Beschrijving> <Type>CodedValue</Type> <DataType>int</DataType> <CodedValueData> <Code>44</Code> <Value>verbinding</Value> <Default>J</Default> </CodedValueData> <CodedValueData> <Code>45</Code> <Value>kruising</Value> <Default>N</Default> </CodedValueData> <RangeData> <Minimum/> <Maximum/> <Default/> </RangeData> <SplitRegel>Duplicate</SplitRegel> <MergeRegel>DefaultValue</MergeRegel> </Domein>

38. Single entity, multiple attributesconstraint ‘att007a’ <AttribuutRegel> <Nummer>att007a</Nummer> <VervolgNummer/> <Categorie/> <Beschrijving>Als Naam_Aweg is ingevuld, dan WegType moet 'autosnelweg' bevatten</Beschrijving> <FoutMelding>WegType bevat niet autosnelweg</FoutMelding> <TriggerNiveau>1</TriggerNiveau> <VervolgOperator/> <FeatureKlasse>EDT_WEG_VLAK</FeatureKlasse> <AlsAttribuut>NAAM_AWEG</AlsAttribuut> <AlsOperator>!=</AlsOperator> <AlsWaarde>""</AlsWaarde> <DanAttribuut>WEGTYPE</DanAttribuut> <DanOperator>MVCONTAINS</DanOperator> <DanWaarde>|autosnelweg|</DanWaarde> </AttribuutRegel>

39. Topology constraint ‘top04’ <AttribuutRegel> <Nummer>top04</Nummer> <VervolgNummer/> <Categorie/> <Beschrijving>Indien Wegvlak overlapt met Wegvlak dan moet HOOGTENIVEAU verschillend zijn</Beschrijving> <FoutMelding>Wegvlak overlapt Wegvlak</FoutMelding> <TriggerNiveau>1</TriggerNiveau> <VervolgOperator/> <FeatureKlasse>EDT_WEG_VLAK</FeatureKlasse> <AlsAttribuut>OBJECTID</AlsAttribuut> <AlsOperator>AREAOVERLAPAREA</AlsOperator> <AlsWaarde>EDT_WEG_VLAK</AlsWaarde> <DanAttribuut>HOOGTENIVEAU</DanAttribuut> <DanOperator>!=</DanOperator> <DanWaarde>FEATURE2.HOOGTENIVEAU</DanWaarde> </AttribuutRegel>

40. Relationship (count)constraint ‘brn01’ <AttribuutRegel> <Nummer>brn01</Nummer> <VervolgNummer/> <Categorie/> <Beschrijving>Iedere feature moet een Bron hebben</Beschrijving> <FoutMelding>Geen Bron</FoutMelding> <TriggerNiveau>1</TriggerNiveau> <VervolgOperator/> <FeatureKlasse>EDT_WEG_VLAK</FeatureKlasse> <AlsAttribuut>OBJECTID</AlsAttribuut> <AlsOperator>&gt;=</AlsOperator> <AlsWaarde>0</AlsWaarde> <DanAttribuut>OBJECTID</DanAttribuut> <DanOperator>BRONCOUNT&gt;</DanOperator> <DanWaarde>0</DanWaarde> </AttribuutRegel>

41. 1. New feature overlaps with existing features 2. No source for feature

42. Some lessons, topographic base data • Own (XML) encoding of constraints, maybe a standard would have been better; e.g. OCL • Same encoding of constraints used in different subsystems: • at data storage side/DBMS check-in and • at data edit side • Constraints not yet included in exchange format: some could possibly included in standard GML/XML; e.g. domains, but more research needed for others

43. Contents • Introduction • Constraints in a landscape design VR system • Constraints in a cadastral data set (topology) • Constraints in a topographic base data set • Constraints in web feature service transactions • Classification of constraints • Support for constraints • Conclusions and further research

44. Constraints in Web Feature Service transactions Applied to case ‘notary drafts Parcel boundary’ MSc-thesis project Thijs Brentjens

45. OGC Web Feature Services (WFS) • Defines interface to retrieve and edit geodata • Based on common web technologies: • HyperText Transfer Protocol (HTTP) • eXtensible Markup Language (XML) • Geography Markup Language (GML) • Basic WFS: Discovering and querying data • Transactional WFS: Insert, Update, Delete, Lock

46. Case study: Notary drafts parcel boundary • Cadastral transaction: • Transfer • Merge • Split • Notary drafts: • Preliminary boundaries • Annotation • Legal after surveying

47. The WFS protocol http://130.161.150.109:8080/geoserver/wfs/wfs?request= DescribeFeatureType&typeName=DRAFT_BOUNDARY,DRAFT_PARCEL • Pose a request (get two types of features): • XML/GML (geo-information, 2-way directions): <gml:MultiLineString srsName= "http://www.opengis.net/gml/srs/epsg.xml#28992"> <gml:lineStringMember> <gml:LineString> <gml:coordinates decimal="." cs="," ts=" "> 106417204,448719275 106367184,448675614 </gml:coordinates> </gml:LineString> </gml:lineStringMember> </gml:MultiLineString> </cad:SHAPE> <cad:OBJECT_ID>341411971</cad:OBJECT_ID> <cad:CLASSIF>31</cad:CLASSIF> <cad:STATUS_CD>0</cad:STATUS_CD>

49. Evaluation of Transactional WFS • WFS enables sharing & editing in heterogeneous, interoperable environment possible • Functions over the Web, limited to simple editing • Beyond simple editing: application logic? • Integrity constraints only on single features, not between features (XML/GML schema encoded) • Transferring (general) constraint knowledge to client not possible • Also constraints on operations (valid actions)? • WFS-T does not support true transactions, as a transaction may be partially successful

50. Contents • Introduction • Constraints in a landscape design VR system • Constraints in a cadastral data set (topology) • Constraints in a topographic base data set • Constraints in web feature service transactions • Classification of constraints • Support for constraints • Conclusions and further research