重要

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19. 使用矢量瓦片

19.1. 什么是矢量瓦片？

矢量瓦片是地理数据包，打包成预定义的大致正方形的 "瓦片" ，便于在Web传输。结合了预渲染的栅格地图瓦片和矢量地图瓦片。矢量瓦片服务器返回矢量地图数据，该数据已被裁剪到每个瓦片的边界，而不是预渲染的地图图像。裁剪的瓦片表示矢量瓦片服务的缩放级别，该缩放级别源自金字塔方式。与非瓦片的矢量地图相比，使用此结构可以减少数据传输。只需传输当前地图视图以及当前缩放级别的数据。此外，与瓦片栅格地图相比，数据传输也大大减少，因为矢量数据通常比渲染的位图小得多。矢量瓦片未分配任何样式信息，因此QGIS需要应用制图样式来显示数据。

../../../_images/vector_tiles_pyramid_structure.png

图 19.1 具有缩放级别的矢量瓦片的金字塔结构

19.2. 支持的格式

通过以下方式支持矢量瓦片：

  • 远程源 (HTTP/S) - 使用XYZ模板 - type=xyz&url=http://example.com/{z}/{x}/{y}.pbf

  • 本地文件 - 使用XYZ模板 - 例如: type=xyz&url=file:///path/to/tiles/{z}/{x}/{y}.pbf

  • 本地MBTile数据库 - 例如: type=mbtiles&url=file:///path/to/file.mbtiles

要将矢量瓦片数据集加载到QGIS，请使用 数据源管理器 对话框中的 addVectorTileLayer 矢量瓦片 选项卡。更多信息，请参阅 使用矢量瓦片服务 。

19.3. 矢量瓦片数据集属性

The vector tiles Layer Properties dialog provides the following sections:

metadata Information

system Source

symbology Symbology[1]

labelingSingle Labels[1]

rendering Rendering

editMetadata Metadata

[1] 也可在 图层样式面板 中使用

19.3.1. 信息属性

Information 选项卡为只读状态，这是引人关注的位置，可以快速获取当前图层的摘要信息和元数据。提供的信息包括：

  • 基于图层的提供程序：名称、URI、源类型和路径、缩放级别的数量

  • 坐标参照系：名称、单位、方法、精度、参照 (即静态还是动态)

  • 从 已填充的元数据 中提取：访问、范围、链接、联系人、历史记录等

19.3.2. 源属性

The system Source tab displays basic information about the selected vector tile, including:

  • the Layer name to display in the Layers Panel;

  • the Coordinate Reference System: Displays the layer's Coordinate Reference System (CRS). You can change the layer's CRS, by selecting a recently used one in the drop-down list or clicking on the setProjection Select CRS button (see Coordinate Reference System Selector). Use this process only if the layer CRS is wrong or not specified.

../../../_images/vector_tiles_source.png

图 19.2 Vector Tiles Properties - Source Dialog

19.3.3. Symbology and Labels Properties

../../../_images/vector_tiles_symbology.png

图 19.3 矢量瓦片图层符号化

19.3.3.1. Setting rules

As vector tiles consist of point, line and polygon geometries, the respective symbols are available. To apply a cartographic style (with symbology and/or labels), you can either:

  • Use a Style URL when creating the Vector Tiles Connection. The symbology will be shown immediately in the symbology Symbology tab after the layer is loaded in QGIS.

  • Or build your own symbology and labeling in the corresponding tabs of the layer properties. By default, QGIS assigns an identical symbol to the features based on their geometry type.

In both cases, setting a style for a vector tile relies on a set of rules applied to the features, indicating:

  • a vector symbol or label

  • a Label, a title for comprehensive identification of the rule

  • the name of a particular Layer the rule should apply to, if not applied to (all layers)

  • a Min. Zoom and a Max. Zoom, for the range of display. Symbology and labeling can be dependent on the zoom level.

  • a Filter, a QGIS expression to identify the features to apply the style to

Each rule is added pressing the symbologyAdd Add rule button and selecting the type of symbols (Marker, Line, Fill) corresponding to the features geometry type. You can as well symbologyRemove Remove selected rules or symbologyEdit Edit current rule.

At the bottom the Current Zoom is shown. Check the unchecked Visible rules only option at the top of the dialog to filter the list of rules to only those that are visible at the current zoom level. This makes it easier to work with complex vector styling and to locate troublesome rules. The search Filter rules text box also helps you easily find a rule, by searching the Label, Layer and Filter fields.

In 图 19.3 we set up style for the OpenStreetMap landuse layer. For better visibility most of the rules are deselected.

19.3.3.2. Layer rendering

From the Symbology tab, you can also set some options that invariably act on all features of the layer:

  • Opacity: You can make the underlying layer in the map canvas visible with this tool. Use the slider to adapt the visibility of your vector layer to your needs. You can also make a precise definition of the percentage of visibility in the menu beside the slider.

  • Blending mode: You can achieve special rendering effects with these tools that you may previously only know from graphics programs. The pixels of your overlaying and underlaying layers are mixed through the settings described in Blending Modes.

19.3.3.3. Styles

Available at the bottom of most of the tabs, the Styles ► menu provides shortcuts to save, load, create, switch styles to apply to the vector tiles. Vector tiles can have their style saved from QGIS as QML files and they can be imported as:

More details at 保存和共享图层属性.

19.3.4. Rendering Properties

Under unchecked Scale dependent visibility, you can set the Maximum (inclusive) and Minimum (exclusive) scales, defining a range of scales in which features will be visible. Out of this range, they are hidden. The mapIdentification Set to current canvas scale button helps you use the current map canvas scale as boundary of the range visibility. See 可见比例选择器 for more information.

../../../_images/vector_tiles_rendering.png

图 19.4 Vector Tiles Properties - Rendering Dialog

19.3.5. 元数据属性

The editMetadata Metadata tab provides you with options to create and edit a metadata report on your layer. See 元数据 for more information.