This extension for the Geoserver adds the possibility to deliver Mapnik Vector Tiles in Protocol Buffers outputformat as result of an WMS or Slippy Map Tile request. This Version (0.3.X) has been developed and tested with Geoserver 2.12 but might also work with preceding versions. Starting with Geoserver 2.14 and its upgrade to Geotools 20.0 this PlugIn will not work because of changes in the used JTS Library Version. For Geoserver Versions 2.14 the migration from jts 1.14 - jts 1.15+ is required. This process will be done in an seperate branch.
The resulting Vector Tiles can e.g. be rendered by WebGL JS clients like Mapbox GL JS or Tangram.
For building the plugin the geoserver source code is required. It is available at the boundless maven repository or on GitHub.
You can build gs-mvt-0.3.X.jar with maven or directly download it from here. In order to get started the gs-mvt-0.3.X.jar package and the depending library protobuf-java-2.6.1.jar have to be copied to the geoserver's lib directory geoserver/WEB-INF/lib. After starting the GeoServer the format application/x-protobuf is shown in the WMS Format list of the layer preview.
Mandatory for the WMS getMap request are the bbox, witdh and height parameters. The bbox describes the requested source coordinate system. The width and height the target coordinate system (tile local). The MVT format uses a local coordinate system within each tile. By default this is 0 to 256 on x and y axis. An example WMS Request could be:
http://localhost/geoserver/test/wms?STYLES=&LAYERS=test:streetsegments&FORMAT=application/x-protobuf&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&bbox=9.499057554653266,46.410057509506515,17.1504898071289,49.0165481567383&WIDTH=256&HEIGHT=256
As result all features of the requested clip are returned. Additionally a TopologyPreservingSimplifier simplifies these geometries. By default the algorithm uses a generalisation factor based on the zoom level. See Generalisation.
The default behaviour of the plugin choose a generalisation factor based on the zoom level. Large zoom levels will be generalised with a smaller factor then smaller ones.
The Plug-In provides 3 sets of different generalisation configurations (LOW,MID,HIGH) which can be selected by adding the gen_level ENV parameter to the WMS request (or apply the parameter to the Slippy Map Tiles Request).
An example WMS Request could be:
http://localhost/geoserver/test/wms?STYLES=&LAYERS=test:streetsegments&FORMAT=application/x-protobuf&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&bbox=9.499057554653266,46.410057509506515,17.1504898071289,49.0165481567383&WIDTH=256&HEIGHT=256&ENV=gen_factor:LOW
Generalisation Configuration
| Zoom | gen_factor - LOW | gen_factor - MID | gen_factor - HIGH |
|---|---|---|---|
| 0 | 0.7 | 0.8 | 1.0 |
| 1 | 0.7 | 0.8 | 1.0 |
| 2 | 0.6 | 0.8 | 1.0 |
| 3 | 0.6 | 0.7 | 1.0 |
| 4 | 0.6 | 0.7 | 1.0 |
| 5 | 0.6 | 0.7 | 1.0 |
| 6 | 0.6 | 0.7 | 1.0 |
| 7 | 0.6 | 0.7 | 0.9 |
| 8 | 0.6 | 0.7 | 0.9 |
| 9 | 0.5 | 0.6 | 0.8 |
| 10 | 0.4 | 0.5 | 0.7 |
| 11 | 0.35 | 0.45 | 0.7 |
| 12 | 0.3 | 0.4 | 0.7 |
| 13 | 0.25 | 0.35 | 0.6 |
| 14 | 0.2 | 0.3 | 0.5 |
| 15 | 0.15 | 0.25 | 0.4 |
| 16 | 0.1 | 0.2 | 0.3 |
| 17 | 0.05 | 0.1 | 0.2 |
| 18 | 0.01 | 0.05 | 0.1 |
| 19 | 0.005 | 0.025 | 0.05 |
| 20 | 0.001 | 0.01 | 0.01 |
per default MID is used
If the configuration shiped in the Plug-In dosn´t suite the needs of a data set or any special behaviour is required the generalisation level can be overwritten by using the WMS ENV parameter gen_factor (or apply the parameter to the Slippy Map Tiles Request). If this factor is present in the WMS Request it will be applied to the generalisation algorithm, the value defined in the generalisation level will not be used in this request.
zero or negative gen_factor can be used to turn the generalisation off!
A typically use case could be:
- fixed generalisation level
- custom generalisation set per zoom level (e.g. in conjunction with a client that alters the factor in the url when the map is zoomed)
- turning generalisation off
An example WMS request could be:
http://localhost/geoserver/test/wms?STYLES=&LAYERS=test:streetsegments&FORMAT=application/x-protobuf&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&bbox=9.499057554653266,46.410057509506515,17.1504898071289,49.0165481567383&WIDTH=256&HEIGHT=256&ENV=gen_level:0.07
Per default the Plug-In will skip small geometries (short lines or polygons with small areas). The treshold is currently fixed with 0.05. This behaviour can be turned changed by setting the WMS ENV Parameter small_geom_threshold to a double value (or apply the parameter to the Slippy Map Tiles Request).
A positive double value means that lines shorter or polygons with a smaller area are skipped in output. If the parameter is zero or negative no geometries will be skipped in output.
Slippy Map Tiles describes the tile format used by Google, Bing and OSM. Usually a tile cache delivers the result to the client. But the GeoWebCache used by the Geoserver does not allow to be extended with additional MimeTypes (e.g. application/x-protobuf) without a change to core classes. Update: In GWC 1.8 the class will be extended and the protobuf MimeType will be supported. Therefore a basic Slippy Map Tile Controller has been provided with this extension, that translates the slippy map tile names into a WMS redirect. The Slippy Tile request has the following format:
http://localhost/geoserver/slippymap/{layers}/{z}/{x}/{y}.{format}
| Path Variable | Description | Type |
|---|---|---|
| layers | layer or layer names | String or comma separated string list |
| z | zoom level | integer |
| x | tile column | integer |
| y | tile row | integer |
| format | output format | one of pbf,png,gif,jpg,tif,pdf,rss,kml,kmz |
To adjust the WMS parameters the following Request Parameters (in query String) are additionally allowed:
| Request Parameter | Description | Type |
|---|---|---|
| buffer | buffer size | integer default 10 |
| tileSize | size of result coordinate system (width and height) | integer default 256 |
| styles | used styles for the layer(s) | String or comma separated Strings if more than one layer |
| time | translated to WMS time parameter | Date String |
| cql_filter | translated to WMS cql_filter parameter | String |
| viewparams | translated to WMS viewparams parameter | String |
| bboxToBoundsViewparam | if set to true adds the WMS bounds as a viewparams value (can than be used e.g. to improve performance in Geoserver SQL Views) | Boolean |
| sld | External Style Sheed Descriptor | URL (Location of SLD to be used) |
| sld_body | Style Description | SLD XML |
| gen_level | generalisation level | String (ENUM) Values LOW/MID/HIGH default MID |
| gen_factor | generalisation factor | Double default null |
| small_geom_threshold | threshold for short lines / small areas, smaller ones then defined will be skipped in output | Double default 0.05 |
http://localhost/geoserver/slippymap/streets/13/4390/2854.pbf?buffer=5&styles=line
Since the vector features are usualy styled on client side only the filter rules and not the symbolizers of a GeoServer Style Sheet (SLD) are considered. Using scale denominators the filter rules can be adjusted so that for example some features are not delivered at higher zoom levels. This prevents unnecessary delivery of features that are not rendered on the client anyway.
Following example shows an GeoServer Style Sheet (SLD) filtering features by a frc value.
<?xml version="1.0" encoding="ISO-8859-1"?>
<StyledLayerDescriptor version="1.0.0" xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc"
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd">
<NamedLayer>
<Name>test_filter</Name>
<UserStyle>
<Name>test</Name>
<Title>Test Filter Style for Geoserver</Title>
<Abstract>A sample style for pbf tiles that filters features according to its frc property</Abstract>
<FeatureTypeStyle>
<FeatureTypeName>Feature</FeatureTypeName>
<Rule>
<MaxScaleDenominator>500000</MaxScaleDenominator>
<ogc:Filter>
<ogc:PropertyIsGreaterThanOrEqualTo>
<ogc:PropertyName>frc</ogc:PropertyName>
<ogc:Literal>3</ogc:Literal>
</ogc:PropertyIsGreaterThanOrEqualTo>
</ogc:Filter>
</Rule>
<Rule>
<MaxScaleDenominator>1000000</MaxScaleDenominator>
<ogc:Filter>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>frc</ogc:PropertyName>
<ogc:Literal>2</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:Filter>
</Rule>
<Rule>
<MaxScaleDenominator>2000000</MaxScaleDenominator>
<ogc:Filter>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>frc</ogc:PropertyName>
<ogc:Literal>1</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:Filter>
</Rule>
<Rule>
<ogc:Filter>
<ogc:PropertyIsEqualTo>
<ogc:PropertyName>frc</ogc:PropertyName>
<ogc:Literal>0</ogc:Literal>
</ogc:PropertyIsEqualTo>
</ogc:Filter>
</Rule>
</FeatureTypeStyle>
</UserStyle>
</NamedLayer>
</StyledLayerDescriptor>In this example features with the property frc=0 are never filtered. All other features containing a frc value are filtered if the requested ScaleDenominator exceeds the defined MaxScaleDenominator.