重要

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29.2.5. トポロジチェッカープラグイン

図 29.14 トポロジチェッカープラグイン

トポロジとは、地理的領域の地物を表すポイント、ライン、およびポリゴン間の関係を表すものです。トポロジチェッカープラグインを使用すると、ベクタファイルを調べて、いくつかのトポロジルールでトポロジを確認することができます。これらのルールは、地物の空間関係がお互いに「等しい」か、「含んでいる」か、「覆っている」か、「覆われている」か、「交わっている」か、「離れている」か、「交差している」か、「重複している」か、「接触している」か、または「範囲内にある」かどうかをチェックします。ベクタデータにどのトポロジルールを適用するかは、個別の質問によります。（たとえば、ラインレイヤのはみ出しは通常は容認しないでしょうが、これが道路の行き止まりを表している場合には、ベクタレイヤからそれらを削除することはしないでしょう）。

QGISには、新たな地物をエラーなしで作成するのに最適な、組み込みのトポロジ編集機能があります。しかし、既存のデータエラーやユーザに起因するエラーを見つけるのは困難です。このプラグインは、ルールのリストを通じてこのようなエラーを見つけるのに役立ちます。

To enable the Topology checker plugin:

1. Go to Plugins menu

2. Open Manage and Install plugins and choose Installed

3. Enable Topology checker

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

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

ポイントレイヤ に対しては、次のルールが利用可能です:

• 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.

ラインレイヤ に対しては、次のルールが利用可能です:

• 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.

ポリゴンレイヤ に対しては、次のルールが利用可能です:

• 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:

  • ポリゴンのリングは閉じている必要があります。

  • 穴を定義するリングは、外側の境界を定義するリングの内側にある必要があります。

  • リングは自己交差してはいけません（互いに接触することも交差することもできません）。

  • リングは、1点で接触する場合を除き、他のリングに接触できません。

• 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 ^{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 ^{Delete selected rules} button.

Press OK and then choose from the Topology checker panel:

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

• or ^{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 Show 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.