1 / 36

ICA Workshop on Geospatial Analysis and Modeling 8 July 2006 Vienna

ICA Workshop on Geospatial Analysis and Modeling 8 July 2006 Vienna. A TOOL PERFORMING TOPOLOGICAL CORRECTION IN GIS. Eva Savina Malinverni - Università Politecnica delle Marche - Ancona (Italy) e.s.malinverni@univpm.it.

niyati
Download Presentation

ICA Workshop on Geospatial Analysis and Modeling 8 July 2006 Vienna

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ICA Workshop on Geospatial Analysis and Modeling 8 July 2006 Vienna A TOOL PERFORMING TOPOLOGICAL CORRECTION IN GIS Eva Savina Malinverni - Università Politecnica delle Marche - Ancona (Italy) e.s.malinverni@univpm.it Stefano Bellesi - Regione Marche - Ancona (Italy) stefano.bellesi@regione.marche.it

  2. GENERALITY THE GIS DATA STRUCTURE THE DATA MAINTENANCE APPLICATIONS

  3. TOPICS 1 ANALYSIS OF THE TOPOLOGICAL INCONSISTENCY IN SPATIAL DATABASES COMING FROM NUMERICAL CARTOGRAPHY ORGANIZED IN INFORMATIVE LAYERS 2 GENERALIZATION IN THE GIS PRESERVING THE CORRESPONDENCES AND THE DATA STRUCTURES IMPLEMENTATION OF A NEW TOOL “TOPOLOGY ”IN A COMMERCIAL SOFTWARE TO SOLVE SOME TOPOLOGICAL PROBLEMS

  4. TYPOLOGIES OF DATA STRUCTURES • VECTOR MODEL:objects which have a position in the space (2D-3D) • TOPOLOGY: spatial relationships among the objects (2D) • ATTRIBUTE: the description of the objects However ……the spatial relations, typically derived from positional information, are often imprecise and they can produce some results in conflict with the geometric representation of the real objects…...

  5. VECTOR MODEL in the sense that object-face relationships are not preserved “NON -TOPOLOGICAL” MODEL The vector model is the most natural computer graphic translation of real objects • Every object is represented by a single entity • Every entity is represented by a single primitive • It is possible to have duplicated primitives Disadvantages: • Redundancies • Incongruities

  6. TOPOLOGICAL MODEL • There are not primitives parzially or totally overlapped • It needs to divide the entities according to the primitives • Different entities can share the same primitives • This type of data manipulation involves concepts such as adjacency, connectivity and containment The topological model repeats the traditional drawing in cartography Advantages: THE SPATIAL RELATIONSHIPS PLAY AN IMPORTANT ROLE IN THE SPATIAL DATABASE, SINCE THEY ARE USUALLY THE BASE FOR A CORRECT USE OF THE QUERIES

  7. A TOPOLOGICAL MODEL CAN BE UNDERSTOOD AS A PLANAR NETWORK THAT DEFINES THE CONNECTION WITH THE FOLLOWING PRIMITIVES nodes arcs polygons

  8. DATA MAINTENANCE REQUIREMENTS TO MAINTAIN RELATIONSHIPS BETWEEN THE PRIMITIVES TO USE TOPOLOGICAL RELATIONS TO DETECT AND CORRECT ERRORS IN GIS DATA SETS Spatial relations are typically derived by data manipulation such that the check of the topological inconsistency involves not only the control of the stored data, but also the control of the data manipulation results

  9. TOPOLOGICAL CORRECTION APPROACH A COMPLETE APPROACH REQUIRES THREE DIFFERENT TASKS: THE DEFINITION OF THE ERRORS THE CHECK OF THE DATABASE THE CORRECTION OF THE ERRORS Since an error is defined as a forbidden topological relation between the objects, the way to correct it will be to create the correct topological relationships between these objects

  10. TOPOLOGICAL INCONSISTENCY THE MOST FREQUENT PROBLEMS WHICH CAN HAPPEN ARE: double and redundant vertices overlapped arcs double and tangent arcs missed tangency between two arcs • Data quality • Computational geometry Why topology is so important?

  11. TOPOLOGICAL CHECK If the datum is already topologically consistent it is possible to create, without mistakes, the topological structure before to verify the correctness of the data from a geometric point of view and successively to create the topological relationships SOME TOPOLOGICAL CONTROLS ARE APPLICABLE TO MONO-DIMENSIONAL ELEMENTS

  12. A TOPOLOGICAL CORRECTION TOOL Some commercial GIS software have some evident gaps performing a topological investigation These software do not deal with topological relations or consider only few relations so that the correction tools do not always work in an automatic way but sometimes require the support of an human operator How to create a correct topological model? MAPINFO PROFESSIONAL 7.5 MAPBASIC 7.0

  13. THE VISUAL INTERFACE FOR END-USERS Menu Toolbar To choice the type of topological checks Message Windows To help and inform about the performances

  14. THE SOFTWARE TOPOLOGY MANY SUBROUTINES PERFORM SPECIFIC TASKS

  15. THE APPLICATION TO A CADASTRAL MAP The first application regards the topological control and correction of a cadastral map related to Genga (Ancona – Italy) at the scale 1:2000

  16. THE DATA ORGANIZATION THE FIRST TASK CREATES THE TABLES TO PERFORM THE TOPOLOGICAL RELATIONSHIPS SUCCESSIVELY Point entity NODE ATTRIBUTE TABLE Linear entity ARC ATTRIBUTE TABLE Region entity POLYGON ATTRIBUTE TABLE

  17. Subroutine ‘ Arctable’ Sub Arctable prepares the data Create Table AAT Create Map For AAT Create Table NAT Create Map For NAT Commit Table AAT Commit Table NAT Alter menu “Table AAT and NAT” End Sub

  18. Node Attribute Table (NAT) The Node Attribute Table contains the corresponding starting and ending nodes

  19. Arc Attribute Table (AAT) The Arc Attribute Table organizes all the linear entities

  20. Polygon Attribute Table (PAT) Polygon Attribute Table (PAT) contains all the areas in the map identified by the coordinates of their own centroid

  21. MONO-DIMENSIONAL ENTITIES CHECK A dedicated dialogue box in the software requires some parameters and a window notifies the found errors USE A CONTROL DISTANCE Delete the double or redundant nodes USE A COLINEARITY DISTANCE Line up the polylines

  22. A message windowrefers how many errors have been localized The buffer value is choice by the end-user OVERLAPPED POLYLINES To recognize the overlapped polylines a buffer is traced around every linear element The found overlapped entities can be: • automatically deleted This verifies that any other polyline is not entirely contained in this area of control • verified and manually deleted • unchanged

  23. Buffer valuebased on the graphic error multiplied by the scale of the map WARNING: if the buffer value is too small, the program requires another value CHECK OF THE PERFECT CLOSURE IN CORRESPONDENCE OF THE NODES Node Attribute Table The nodes are counted at least twice Topological error correction • buffer around the node • test of the presence of another node or polyline • closure of the polylines

  24. MISSED TANGENCY Node of a polyline next to an arc USE A CONTROL DISTANCE A way to correct such an error is to create an intersection point and to split the polyline in the tangent points

  25. BI-DIMENSIONAL ENTITIES CHECK Area containing holes inside Overlapped Areas REGION topological control Test the adjacency of every area Bi-dimensional entities directly depend on the mono-dimensional ones The HOLE is filled The software automaticallyverifies the exixtence of the overlaps If these entities do not contain topological errors also the areas are correct The overlapped areas are highlighted and cut USE A THRESHOLD VALUE TO IDENTIFY THE HOLE

  26. SOME REMARKS The use of the program has underlined two problems during the correction phases ONE REGARDS THE OPENED ARCS WITHOUT INTERSECTION They are not automatically removed, but the operator, examining the map, decides to make some changes and the procedure can be iterated SECOND ONE REGARDS THE CLOSURE OF ARCS IN CORRESPONDENCE OF THE NODES Where the control area value is too small to perform the closure, it is necessary to perform a manual correction

  27. GENERALIZATION OF TECHNICAL MAPS AT DIFFERENT SCALES The aim of this other application regards the construction, representation and generalization in the GIS of different map scales by standard procedure, preserving the correspondences and the data structures GENERALIZATION changes the representation of scale-dependent phenomena, eliminating redundant details and simplifying the appearance and density of objects to improve the analysis capabilities DB 1:10.000 RESPECT TOPOLOGICAL RULES DB 1:25.000

  28. CASE OF STUDY To derive from a correct data structure at the scale 1:10.000 a new valid geometric and topological data structure suitable to the scale 1:25.000 LAYER : ROADS AND RAILWAYS Marche Region Technical Maps at the scale 1:10.000 (DB10, year 1999) IGMI new maps at the scale 1:25.000 (DB25, year 1993) AN IMPORTANT REQUIREMENT Topological consistency must be maintained both within individual features and among the co-displayed features for all the scales at which they may be retrieved

  29. ROAD NETWORK REPRESENTATION BY NODES AND ARCS List of all the features in the map organized by code, description and geometric primitives In the DB25 there are much more classes than in the DB10 and different types of symbolic representations

  30. DEFINITION AND COMPARISON OF THE ENTITIES ROAD AND RAILWAY Verify network scheme by the specifications of the map DB 1:10.000 DB 1:25.000 POLYLINE FEATURES TOPOLOGICAL RECONSTRUCTION POLYLINE FEATURES POINT FEATURES TOPOLOGICAL RULES OK POINT FEATURES POINT FEATURES EXISTING TOPOLOGY POLYGON FEATURES POLYGON FEATURES

  31. DB25 NETWORK SCHEME CONSTRUCTION To construct the symbology correctly and to test the polylines we used a specific buffer value POLYLINES DB 1:10.000 CHECK OF THE OVERLAPPED AREAS BUFFER HALF VALUE OF THE SYMBOL HALF VALUE OF THE TOLERANCE ROAD SYMBOLIC REPRESENTATION THE OVERLAPPED AREAS ARE DELETED AND THE POLYLINES SHIFTED NOTE: THE RAILWAY, REPRESENTED BY POLYLINES, USES AS BUFFER ONLY THE TOLERANCE VALUE

  32. The change of the network scheme risks to lose the topological consistency of the data structure THREE POSSIBLE CASES OF ALTERATION case (a) deletes a non connected arc case (b) detects two new dangle nodes (regarding the bridge) which are automatically corrected by means of a tolerance value case (c) simplifies the intersections POLYLINE FEATURES TOPOLOGICAL RECONSTRUCTION (case b) POLYLINE FEATURES POINT FEATURES

  33. USE OF THE GRAPH TO REALIZE A CORRECT SYMBOLIC REPRESENTATION Completed the generalization we have constructed the layers related to the railway, bridges and roads

  34. SOME REMARKS NO BUFFER FLAT MAPINFO SOFTWARE DISADVANTEGES NO MERGE NO CHECK on lines and symbols of millimeter size NEW DEVELOPMENTS OF THE TOOL “TOPOLOGY” ADDING MORE COMMANDS RECONSTRUCTION OF OTHER NETWORKS HYDROGRAPHY TECHNOLOGICAL NETWORKS AND SO ON

  35. CONCLUSIONS The increase of automatic procedures needs to standardize entity definitions with their spatial and logical relationships Line and polygon generalization procedures must guarantee simplifications topologically consistent It’s necessary, to fix for each entity in every different scale the type of representation (symbolical or real measure), the metric tolerance (graphic error, minimum surface) and the possible characteristic of the object (shape) A further topic of future research is the development of incremental update procedures to maintain large databases of topologically consistent multi-scaledata

  36. Thank you for your attention

More Related