Oregon Relational Spatial Topology ORST Representation

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Oregon Relational Spatial Topology (ORST)
Representation

• By
• David Hunt
• Research guided by Dr. Minoura

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Intro

• ORST- DB representation for storing geometry day
  used within GIS applications
• Designed parser for a proprietary third data
  format
• Implemented spatial manipulation features for
  polygon data

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Technology

• Postgres
• PostGIS
• PHP
• JavaScript

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GIS

• Geographic Information System
• WebGD
• Google Earth
• County, City, State, World

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Applications

• Cadastral
• Disaster relief
• Crime statistics
• Commerce
• Etc.

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Geometry objects

• POINT
• X Y coordinate pair
• (1 5)

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Geometry objects

• LineString/Arc
• Collection of points
• (11, 5 1, 5 5)

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Geometry Objects

• Polygon/MultiPolygon
• Collection of lines strings
• (((1 1, 5 1, 5 5,1 5, 1 1)))
• First and last point must match

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Geometry Objects

• What is a hole?
• (((1 1, 5 1, 5 5 , 1 5, 1 1), (2 2, 4 2, 4 4, 2
  4, 2 2)))

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GIS Application Usage??

• Add features
• Points
• Lines
• Polygons
• Insertion is controlled

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Relating the Geometries

• We have the below set of polygons.
• How can they be related?

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Relating the Geometries

• Label points and arcs of each polygon
• Give only one label for points and arcs shared by
  polygons.
• Graphical representation of ORST.

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Relating the Geometries

• ORST ERD

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ORST

• Easy to use ORST if using new data.
• What if data already exists?
• Format not always controllable
• What is the most common data format.
• ESRI Shapefile

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ESRI

• Who is ESRI?
• What is a shapefile?
• Geospatial vector format
• Does not explicitly represent topological
  relations

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Shapefile

• Polygons in a shapefile
• Only polygon data
• No arcs and points
• MULTIPOLYGON(((7484618.05180716
  335828.990845255,7488367.78663952
  334126.654085287,7487669.20970841
  336977.533051373,7485769.42293307
  337978.739260576,7484618.05180716
  335828.990845255)))

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Shapefile

• How do we get Shapefile data into ORST.
• Make a coverage
• Use E00 Format

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E00

• What is E00?
• Propriety text format representation of coverage
  data.
• Partial publication of E00 specification has been
  done.
• How do you get an E00 file?

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Format of E00

• ARC sets of data on the arcs
• CNT center points of the polygons
• LAB sets of labels for polygons
• LOG coverage edit history
• PAL repeating sets of data on the polygons
• PRJ map projection data
• SIN spatial index
• TOL multiple lines defining the tolerance type,
  the tolerance status, and the tolerance value
• TXT annotations
• TX6/TX7 annotations
• RXP associations of polygons within a region
  and the PAL section
• RPL - sets of data on the polygons for regions
• PAT attributes for polygon

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Format of E00

• Only ARC and RPL sections essential
• Other sections have potential use for other
  manipulation features.

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ARC

• 1 1 5 1 -1 3
  3
• 6.00000000000000E06 6.00000000000000E05
• 6.00000000000000E06 1.00000000000000E05
• 1.00000000000000E06 1.00000000000000E05
• 1.00000000000000E06 6.00000000000000E05

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ARC

• 1 1 5 1 -1 3
  3
• 1 coverage number not converted
• 1 coverage ID not converted
• 5 from node id of the first point in the
  current arc
• 1 to node id of the last point in the current
  arc
• -1 left polygon id of the polygon on the left
  of the arc
• 3 right polygon id of the polygon on the
  right of the arc
• 3 number of coordinates number of point
  geometries in the arc

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RPL

• 3 1.00000000000000E06 1.00000000000000E05
  6.00000000000000E06 6.00000000000000E05
• 7 0 0 -5 0
  0
• -4 0 0
• 3 number of arcs in the current polygon
• 1.00000000000000E06 x min of the current
  polygon
• 6.00000000000000E05 y min of the current
  polygon
• 6.00000000000000E06 x max of the current
  polygon
• 6.00000000000000E05 y max of the current
  polygon

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RPL

• 7 0 0 -5 0
  0
• -4 0 0
• 7 Arc_Id ID of the arc contained in the
  current polygon
• 0 From_Node_Id - not converted
• 0 Adjacent_Polygon_Id - not converted

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RPL

• What if polygon has a hole?

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Parsing E00

• How did I use the E00 file?
• Took advantage of the structured format to parse
  file
• Noticed that data we worked with contained only a
  single region
• Allowed for parsing the RPL section instead of
  PAL
• Do not need to use data in PAT section.
• Able to use id from original shapefile to link
  attributes.

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Parsing E00

• Create SQL statements to populate ORST
  representation.
• Coordinates in ARC section populated table point
• Used arcs contained in ARC section for table arc
• RPL section used to populate table poly_arc
• Table poly is populated by using the ordering of
  arcs for a polygon in the RPL section

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Parsing E00

• Why not use something out there?
• Final output not compatible with ORST
• Output just more readable
• Converts into other formats
• Required installing a full blown GIS application
• Used entire file

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What is ORST Good for

• User can manipulate polygons while maintaining
  the relationships dynamically
• Move Point
• Merge Polygons
• Split Polygon
• Can be implemented in GIS applications that
  already support some spatial operations
• WEBGD

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Spatial Operations

• Why might we desire operations such as
• Move point
• Merge polygons
• Split polygon
• Do such operations already exists?

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Move Point

• Currently only moving end points

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Move Point

• Find all arcs adjacent to point
• Update arc geometries with new point in table arc
• Update geometry for point in table point
• Use arc ids to obtain all polygons affected by
  move.
• Update geometry of polygon

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Merge Polygons
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Merge Polygons

• Arcs of new polygon
• arcs(P3) (arcs(P1) ? arcs(P2)) (arcs(P1) ?
  arcs(P2))
• Done completely with SQL

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Merge Polygons

• Remove selected arc
• Must also delete any arcs that are connected to
  this arc that share the same polygon. (case c of
  image)
• Delete end points no longer used

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Merge Polygons

• Create new polygon
• Update existing arcs left and right polygon
  attributes
• Update polygon that arcs are associated with
• Remove the merged polygons

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Split Polygon

• Single polygon becomes two polygons
• Split line does not have to be straight
• a) Splitting polygon P1 by intersecting arc A1
  and A3.

b) Splitting polygon P1 by intersecting arc A1
twice.
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Split Polygon

• Use split arc to calculate intersection points
• Obtain arcs that were not intersected by split
• Calculate new arcs from the split arc(s)
• Create new polygons

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Split Polygon

• Insert new arcs in table arc and entries in table
  poly_arc
• Delete split polygon
• Update data for left or right polygon of arc(s)
  that were intersected by the split arc
• Delete intersected arc(s)

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Conclusion

• Coverage data can be maintained with an
  open-source DBMS
• Reduce errors caused by manipulation features not
  stored in a coverage representation such as ORST.

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QA

• Thanks
• Have a great Labor Day