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Spatial Information Systems (SIS) COMP 30110 Formats and Standards

Spatial Information Systems (SIS) COMP 30110 Formats and Standards. Standards and Formats. GIS vendors provide their own proprietary formats Examples : Shapefile (ESRI ArcView format): based on a non-topological representation (as for spaghetti data structure)

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Spatial Information Systems (SIS) COMP 30110 Formats and Standards

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  1. Spatial Information Systems (SIS) COMP 30110 Formats and Standards

  2. Standards and Formats GIS vendors provide their own proprietary formats Examples: Shapefile (ESRI ArcView format): based on a non-topological representation (as for spaghetti data structure) Coverages (ESRI ArcInfo format): based on a topological representation DXF (Drawing Interchange Format: developed within Autodesk’s AutoCAD sw) etc.

  3. Shapefiles Shapefile (ESRI ArcView format): based on a non-topological representation (as for spaghetti data structure) Topological/connectivity relations are calculated on-the-fly A map is composed of different layers (non-overlayed approach) Idrography layer Road network layer Entities from the two layers intersect

  4. Note ArcView is a desktop GIS: Used for visualisation more than for map making Does not provide all full functionality provided by ArcInfo Easily integrates with other applications, DBMSs etc. ArcInfo is a dedicated GIS system: Used more for map making Provides complete GIS functionality It was not designed to be integrated with other applications No high-level (SQL-like) query language

  5. Standards and Formats (cont.d) Formats defined by official organisations (standards): TIGER (Topologically Integrated Geographic Encoding and Referencing): system and DB developed by the US Census Bureau: based on topological representation SDTS (Spatial Data Transfer Standard: developed by the US Geological Survey): based on a complex topological representation etc.

  6. TIGER files Based on topological representation All objects in one single layer: overlayed approach All intersections are stored explicitly even if they do not correspond to geographic objects This intersection point is stored explicitly (i.e., lines are split)

  7. TIGER files (cont.d) • Based on topological representation • Entities: • points • chains (endnodes and shape points) • polygons • Relations: • VE • FE • EV • EF • Additional information: polygon centroids, attribute information, isolated points, dangling edges, etc.

  8. x-y>0^ x<7^ y>1^ y<3^ Other ways of representing vector data: Half-plane representation Half plane representation: polygons are defined as intersection of a number of half planes (each corresponding to one of their sides) The points that belong to the interior of the polygon satisfy the constraints aix+biy<0 (corresponding to half planes) Example:

  9. Other ways of representing vector data: Realms (Güting and Schneider 1993) Realms: planar graphs defined over discrete domains (i.e., grids - not the Euclidean plane) Realm objects: points, lines and regions defined in terms of finite representations Lines and regions defined in terms of realm points and segments Intersections of lines occur only at realm points

  10. Realms (cont.d) Intersections of lines occur only at realm points Therefore a realm is represented by means of a set of points and a set of non-intersecting segments (they only “touch” at their endpoints)

  11. Realms (cont.d) A realm

  12. Realms: remarks More complicated sets of data: not just a polygonal subdivision but also isolated points and dangling edges (inside and outside faces) Classical data structures (e.g., DCEL) must be extended to be able to capture these cases

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