Snapping¶

QWC2 ships a plugin for snapping support while drawing (redlining / measuring / editing). To enable it, make sure the SnappingSupport plugin is enabled in appConfig.js (see the sample sample js/appConfig.js). Then, for each theme for which you want snapping to be available, you can add a snapping block to your theme item in themesConfig.json as follows:

...
"snapping": {
  "snaplayers": [
    {
      "name": "<layername>",
      "min": <min_scale>,
      "max": <max_scale>
    }
  ],
  "featureCount": <feature_count>,
  "wfsMaxScale": <wfs_max_scale>
}
...

where:

• layername is the name of the theme sublayer from which to retreive the snapping geometries.
• min is the minimum scale denominator (inclusive) from which this layer should be used for snapping.
• max is the maximum scale denominator (exclusive) up to which this layer should be used for snapping.
• feature_count is the maximum number of snapping geometries to retreive for the current map extent (default: 500).
• wfs_max_scale is the maximum scale denominator (exclusive) up to which loaded WFS layers should be used for snapping.

Note: Snapping works by querying the geometries of all snapping layers inside the scale range via WMS GetFeatureInfo and refreshing the geometries every time the map extent changes. Therefore, it is recommended to ensure the geometry complexity of the snap layers is appropriate for the specified scale ranges to avoid overloading the server with the GetFeatureInfo requests. Also, the QGIS project will need to be configured so that snap layers are queryable and that feature info responses contain geometries.

For the Redlining, Measure and Editing plugins, the availability of snapping can be independently configured:

{
  "name":"<Redlining|Measure|Editing>",
  "cfg": {
    "snapping": <true|false>,
    "snappingActive": <true|false>,
    ...
  }
}

where:

• snapping determines whether snapping is available for the specified plugin
• snappingActive determines whether snapping is active by default for the specified plugin

When snapping is available, a small toolbar appears on the bottom border of the map with the possibility to toggle snapping.