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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 A TOOL PERFORMING TOPOLOGICAL CORRECTION IN GIS Stefano Bellesi Stefano Bellesi - Regione Marche - Ancona (Italy) Eva Savina Malinverni Eva Savina Malinverni - Università Politecnica delle Marche - Ancona (Italy)

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GENERALITY THE GIS DATA STRUCTURE THE DATA MAINTENANCE APPLICATIONS

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TOPICSTOPICS ANALYSIS OF THE TOPOLOGICAL INCONSISTENCY IN SPATIAL DATABASES COMING FROM NUMERICAL CARTOGRAPHY ORGANIZED IN INFORMATIVE LAYERS 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

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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 ……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…... However

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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 object is represented by a single entity Every entity is represented by a single primitive Every entity is represented by a single primitive It is possible to have duplicated primitives It is possible to have duplicated primitives VECTOR MODEL Redundancies Incongruities Disadvantages: in the sense that object-face relationships are not preserved

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There are not primitives parzially or totally overlapped There are not primitives parzially or totally overlapped It needs to divide the entities according to the primitivesIt needs to divide the entities according to the primitives Different entities can share the same primitives Different entities can share the same primitives This type of data manipulation involves concepts such as adjacency, connectivity and containmentThis 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 TOPOLOGICAL MODEL

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A TOPOLOGICAL MODEL CAN BE UNDERSTOOD AS A PLANAR NETWORK THAT DEFINES THE CONNECTION WITH THE FOLLOWING PRIMITIVES nodesarcspolygons

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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

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TOPOLOGICAL CORRECTION APPROACH A COMPLETE APPROACH REQUIRES THREE DIFFERENT TASKS: THE DEFINITION OF THE ERRORS THE CHECK OF THE DATABASE THE CHECK OF THE DATABASE THE CORRECTION OF THE ERRORS THE CORRECTION OF THE ERRORS A COMPLETE APPROACH REQUIRES THREE DIFFERENT TASKS: THE DEFINITION OF THE ERRORS THE CHECK OF THE DATABASE THE CHECK OF THE DATABASE THE CORRECTION OF THE ERRORS 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

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

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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

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MAPINFO PROFESSIONAL 7.5 MAPBASIC 7.0 MAPINFO PROFESSIONAL 7.5 MAPBASIC 7.0 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?

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

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MANY SUBROUTINES PERFORM SPECIFIC TASKS THE SOFTWARE TOPOLOGY

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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

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

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Subroutine Arctable Subroutine Arctable Sub Arctable Create Table AAT Create Table NAT Create Map For AAT Create Map For NAT Commit Table AAT Commit Table NAT Alter menu Table AAT and NAT End Sub prepares the data

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

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

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

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

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To recognize the overlapped polylines a buffer is traced around every linear element This verifies that any other polyline is not entirely contained in this area of control The buffer value is choice by the end-user OVERLAPPED POLYLINES The found overlapped entities can be: ٠ automatically deleted ٠ verified and manually deleted ٠ unchanged A message window refers how many errors have been localized

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Topological error correction Node Attribute Table The nodes are counted at least twice ٠ buffer around the node ٠ test of the presence of another node or polyline ٠ closure of the polylines Buffer value based 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

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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 MISSED TANGENCY

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

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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

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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 OF TECHNICAL MAPS AT DIFFERENT SCALES AT DIFFERENT SCALES GENERALIZATION OF TECHNICAL MAPS AT DIFFERENT SCALES AT DIFFERENT SCALES GENERALIZATION changes the representation of scale-dependent phenomena, eliminating redundant details and simplifying the appearance and density of objects to improve the analysis capabilities DB1: DB1: RESPECT TOPOLOGICAL RULES RESPECT

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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 Marche Region Technical Maps at the scale 1: (DB10, year 1999) IGMI new maps at the scale 1: (DB25, year 1993) Marche Region Technical Maps at the scale 1: (DB10, year 1999) IGMI new maps at the scale 1: (DB25, year 1993) CASE OF STUDY LAYER : ROADS AND RAILWAYS To derive from a correct data structure at the scale 1: a new valid geometric and topological data structure suitable to the scale 1: AN IMPORTANT REQUIREMENT

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

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ROAD AND RAILWAY DB 1: TOPOLOGICAL RECONSTRUCTION RECONSTRUCTIONTOPOLOGICAL DB 1: POLYLINE FEATURES POINT FEATURES POLYGON FEATURES POLYLINE FEATURES POINT FEATURES POLYGON FEATURES POINT FEATURES Verify network scheme by the specifications of the map DEFINITION AND COMPARISON OF THE ENTITIES EXISTINGTOPOLOGYEXISTINGTOPOLOGY

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

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

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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

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

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CONCLUSIONSCONCLUSIONS 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 Its 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-scale data

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Thank you for your attention Thank you for your attention

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