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29.2.5. 위상 점검기 플러그인

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그림 29.14 위상 점검기 플러그인

위상(topology)이란 지리적 지역의 객체를 표현하는 포인트, 라인 및 폴리곤 간의 관계를 말합니다. 위상 점검기 플러그인을 사용해서 사용자 벡터 파일을 살펴보고 여러 위상 규칙을 기준으로 위상을 점검할 수 있습니다. 이런 규칙들은 사용자 객체가 서로 ‘동등(equal)’ 한지, ‘포함(contain)’ 하는지, ‘커버(cover)’ 하는지, ‘커버되는(CoveredBy)’ 지, ‘공간교차(cross)’ 하는지, ‘분절(disjoint)’ 되는지, ‘교차(intersect)’ 하는지, ‘중첩(overlap)’ 하는지, ‘접촉(touch)’ 하는지, 또는 서로의 ‘내부(within)’ 에 있는지 그 공간 관계를 점검합니다. 이 관계는 사용자 벡터 데이터에 개별적으로 어느 위상 규칙을 적용하느냐에 따라 달라집니다. (예를 들면, 일반적으로 라인 레이어에서는 오버슛(overshoot)을 허용하지 않지만, 오버슛이 막다른 길을 표현하는 경우 사용자 벡터 레이어에서 제거하지 않을 것입니다.)

QGIS는 위상 편집 기능을 내장하고 있는데, 오류가 없는 새 객체를 생성하는 데 매우 유용합니다. 그러나 기존 데이터의 오류 및 사용자가 발생시킨 오류를 찾기란 어렵습니다. 이 플러그인을 사용하면 일련의 규칙을 통해 그런 오류들을 찾을 수 있습니다.

To enable the Topology checker plugin:

  1. Go to Plugins menu

  2. Open showPluginManager Manage and Install plugins and choose pluginInstalled Installed

  3. Enable checkbox topologyChecker Topology checker

  4. Close the Plugin manager dialog. A topologyChecker Topology checker entry is added to the Vector menu.

After you enabled topologyChecker Topology checker open it and choose options Configure to create your topology rules.

포인트 레이어 상에서 다음 규칙들을 사용할 수 있습니다:

  • Must be covered by: Here you can choose a vector layer from your project. Points that aren’t covered by the given vector layer occur in the ‘Error’ field.

  • Must be covered by endpoints of: Here you can choose a line layer from your project.

  • Must be inside: Here you can choose a polygon layer from your project. The points must be inside a polygon. Otherwise, QGIS writes an ‘Error’ for the point.

  • Must not have duplicates: Whenever a point is represented twice or more, it will occur in the ‘Error’ field.

  • Must not have invalid geometries: Checks whether the geometries are valid.

  • Must not have multi-part-geometries: All multi-part points are written into the ‘Error’ field.

라인 레이어 상에서 다음 규칙들을 사용할 수 있습니다:

  • End points must be covered by: Here you can select a point layer from your project.

  • Must not have dangles: This will show the overshoots in the line layer.

  • Must not have duplicates: Whenever a line feature is represented twice or more, it will occur in the ‘Error’ field.

  • Must not have invalid geometries: Checks whether the geometries are valid.

  • Must not have multi-part geometries: Sometimes, a geometry is actually a collection of simple (single-part) geometries. Such a geometry is called multi-part geometry. If it contains just one type of simple geometry, we call it multi-point, multi-linestring or multi-polygon. All multi-part lines are written into the ‘Error’ field.

  • Must not have pseudos: A line geometry’s endpoint should be connected to the endpoints of two other geometries. If the endpoint is connected to only one other geometry’s endpoint, the endpoint is called a pseudo node.

폴리곤 레이어 상에서 다음 규칙들을 사용할 수 있습니다:

  • Must contain: Polygon layer must contain at least one point geometry from the second layer.

  • Must not have duplicates: Polygons from the same layer must not have identical geometries. Whenever a polygon feature is represented twice or more it will occur in the ‘Error’ field.

  • Must not have gaps: Adjacent polygons should not form gaps between them. Administrative boundaries could be mentioned as an example (US state polygons do not have any gaps between them…).

  • Must not have invalid geometries: Checks whether the geometries are valid. Some of the rules that define a valid geometry are:

    • 폴리곤 고리는 닫혀 있어야만 합니다.

    • 구멍을 정의하는 고리는 외부 경계선을 정의하는 고리 내부에 있어야만 합니다.

    • 고리가 스스로 교차해서는 안 됩니다. (혼자 접촉하거나 공간교차해서는 안 됩니다.)

    • 고리는 한 포인트에서 접촉하는 경우 외엔 서로 접촉해서는 안 됩니다.

  • Must not have multi-part geometries: Sometimes, a geometry is actually a collection of simple (single-part) geometries. Such a geometry is called multi-part geometry. If it contains just one type of simple geometry, we call it multi-point, multi-linestring or multi-polygon. For example, a country consisting of multiple islands can be represented as a multi-polygon.

  • Must not overlap: Adjacent polygons should not share common area.

  • Must not overlap with: Adjacent polygons from one layer should not share common area with polygons from another layer.

When you create a New rule click on the symbologyAdd Add rule to include it to the Current rules. You can enable or disable individual rules by clicking on the checkbox. Right-clicking over a rule provides the following options:

  • Select All the rules

  • Activate or Deactivate the selected rules

  • Toggle activation of selected rules

  • Delete selected rules. This can also be achieved with the symbologyRemove Delete selected rules button.

Press OK and then choose from the Topology checker panel:

  • validateAll Validate All: applies the active rules to all the features of the involved layer(s)

  • or validateExtent Validate Extent: applies the active rules to the features of the involved layer(s), within the current map canvas. The button is kept pushed and the results will update as the map canvas extent changes.

Errors will show up in the table of results containing type of error, layer and feature ID. Use Filter errors by rule menu to filter the errors to a specific error type.

Check checkboxShow errors on the canvas to show error location on the canvas. Clicking a row in the table will zoom the map canvas to the concerned feature, where you can use QGIS digitizing tools to fix the error.