doc:geometry-relations

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Documentation | Other Specifications | **Geometry Relations**

TatukGIS supports a powerful, yet easy to manage, mechanism for querying against spatial relationships between two shapes. This mechanism is known as the Dimensionally Extended 9 Intersection Model (DE-9IM)

The idea is to manage a 9 element mechanism in which each element defines the relationship possibilities between the interiors, exteriors, and boundaries of two shapes. The relationship is defined in terms of intersection types, or lack of an intersection.

The meanings of interior, exterior, and boundary, as they relate to shape types, are defined as follows:

Interior | Boundary | Exterior | |
---|---|---|---|

TGIS_Point | Point itself | Nothing | All except Interior |

TGIS_Multipoint | Points themselves | Nothing | All except Interior |

TGIS_Arc (lines) | Line itself except starting/ending points | Starting & ending points of line | All except Interior & Boundary |

TGIS_Polygon (areas) | Area of polygon | Outline of polygon | All except Interior & Boundary |

The nature of the shape intersections is defined by a set of interior, boundary, and exterior relationship possibilities, forming a 3×3 table.

A\B | Interior | Boundary | Exterior |
---|---|---|---|

Interior | * | * | * |

Boundary | * | * | * |

Exterior | * | * | * |

The table can be represented by a string (row-by-row) like:

"T*F**FFF*"

Each element of the table represents an intersection possibility:

Type | Description |
---|---|

T | Intersection exists |

F | Intersection does not exist |

* | Does not matter |

0 | Intersection is a point (dimension = 0) |

1 | Intersection is a line(dimension = 1) |

2 | Intersection is a polygon (dimension = 2) |

2017/02/11 10:27