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Exercise 4 - Tiles of geospatial data via OGC API - Tiles

OGC API - Tiles provides a Web API to deliver tiles of geospatial information. Different forms of geospatial information are supported, such as tiles of vector features ("vector tiles"), coverages, maps (or imagery) and potentially eventually additional types of tiles of geospatial information. The standard is available on this document:

Note

OGC API - Tiles extends the collections/* URL structure (tilesets are listed under /collections/example/tiles:

https://demo.pygeoapi.io/collections/lakes/tiles/WorldCRS84Quad/{tileMatrix}/{tileRow}/{tileCol}?f=mvt

pygeoapi support

pygeoapi supports the core OGC API - Tiles specification, and is able to advertise an existing tileset. Note that pygeoapi itself does not render tiles from source data. It supports publishing pre-rendered tiles from a static url or from a tile server with a xyz url template.

Note

The OGC API - Tiles URL structure is compatible with XYZ layers in common libraries such as OpenLayers, Leaflet and MapML

Note

See the official documentation for more information on supported tile backends

Publish pre-rendered vector tiles

In this scenario, tiles must be pre-rendered before serving. Existing tools to create tiles include, but are not limited to:

For this exercise, you will publish a vector dataset of the greater Hyderabad municipal corporation ward boundaries, from the location below:

  • data: workshop/exercises/data/greater_hyderabad_municipal_corporation_ward_Boundaries.geojson

Let's generate the tiles as the first step using tippecanoe:

Using tippecanoe to generate vector tiles

cd workshop/exercises
docker run -it --rm -v $(pwd)/data:/data emotionalcities/tippecanoe \
tippecanoe --output-to-directory=/data/tiles/ --force --maximum-zoom=16 --drop-densest-as-needed --extend-zooms-if-still-dropping --no-tile-compression /data/greater_hyderabad_municipal_corporation_ward_Boundaries.geojson


cd workshop/exercises
docker run -it --rm -v ${pwd}/data:/data emotionalcities/tippecanoe tippecanoe --output-to-directory=/data/tiles/ --force --maximum-zoom=16 --drop-densest-as-needed --extend-zooms-if-still-dropping --no-tile-compression /data/greater_hyderabad_municipal_corporation_ward_Boundaries.geojson

Update the pygeoapi configuration

Open the pygeoapi configuration in a text editor. Add a new dataset section as follows:

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    hyderabad:
        type: collection
        title: Greater Hyderabad Municipal Corporation ward boundaries
        description: The city ward boundaries represent the administrative and electoral boundary areas of the city. It plays a great role in planning of the city, for each council of the municipal corporation.
        keywords:
           - Boundaries
           - Administrative
           - Ward
        links:
            - type: text/html
              rel: canonical
              title: information
              href: https://livingatlas-dcdev.opendata.arcgis.com/datasets/a090c89d52f1498f96a82e97b8bfb83e_0/about
              hreflang: en-US
        extents:
            spatial:
                bbox: [78.2379194985166180,17.2908061510471995,78.6217049083810764,17.5618443356918768]
                crs: http://www.opengis.net/def/crs/OGC/1.3/CRS84
            temporal:
                begin: 2011-11-11
                end: null  # or empty
        providers:
            - type: feature
              name: GeoJSON
              data: /data/greater_hyderabad_municipal_corporation_ward_Boundaries.geojson
              id_field: objectid
            - type: tile
              name: MVT
              data: /data/tiles
              options:
                metadata_format: tilejson # default | tilejson
                zoom:
                    min: 0
                    max: 16
                schemes:
                    - WorldCRS84Quad
              format:
                    name: pbf
                    mimetype: application/vnd.mapbox-vector-tile

Save the file and restart Docker Compose. Navigate to http://localhost:5000/collections to evaluate whether the new dataset has been published.

Additional check for the following tile specific endpoints in the Hyderabad collection:

TileSet

Publish vector tiles from Elasticsearch

Elasticsearch provides a middleware that renders an index on the fly, as vector tiles. This middleware is also supported by the pygeoapi mvt backend.

If you want to explore publishing vector tiles using Elasticsearch clone this fork of pygeoapi:

git checkout -b ogcapi-ws https://github.com/doublebyte1/pygeoapi.git

Then change into the docker/examples/elastic folder, and run the docker-compose file:

cd docker/examples/elastic

docker-compose up

This configuration, enables publishing greater_hyderabad_municipal_corporation_ward_boundaries.geojson as both OGC API - Features and OGC API - Tiles:

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    greater_hyderabad_municipal_corporation_ward_boundaries:
        type: collection
        title: Greater Hyderabad Municipal Corporation ward boundaries
        description: The city ward boundaries represent the administrative and electoral boundary areas of the city. It plays a great role in planning of the city, for each council of the municipal corporation.
        keywords:
           - Boundaries
           - Administrative
           - Ward
        links:
            - type: text/html
              rel: canonical
              title: information
              href: https://livingatlas-dcdev.opendata.arcgis.com/datasets/a090c89d52f1498f96a82e97b8bfb83e_0/about
              hreflang: en-US
        extents:
            spatial:
                bbox: [78.2379194985166180,17.2908061510471995,78.6217049083810764,17.5618443356918768]
                crs: http://www.opengis.net/def/crs/OGC/1.3/CRS84
            temporal:
                begin: 2011-11-11
                end: null  # or empty
        providers:
            - type: feature
              name: Elasticsearch
              # note: elastic_search is the Docker container name as defined in docker-compose.yml
              data: http://elastic_search:9200/greater_hyderabad_municipal_corporation_ward_boundaries
              id_field: objectid
            - type: tile
              name: MVT
              data: http://elastic_search:9200/greater_hyderabad_municipal_corporation_ward_boundaries/_mvt/geometry/{z}/{x}/{y}?grid_precision=0
              # index must have a geo_point
              options:
                metadata_format: none # default | tilejson
                zoom:
                    min: 0
                    max: 16
                schemes:
                    - WorldCRS84Quad
              format:
                    name: pbf
                    mimetype: application/vnd.mapbox-vector-tile

Client access

QGIS

QGIS supports OGC API Vector Tiles via the Vector Tiles Layer. Although OGC API - Tiles are not natively supported, you can customize the generic connection in order to access them in QGIS.

Access OGC API Vector Tiles from QGIS

Before entering QGIS, access your pygeoapi installation page on the browser and follow these steps.

Follow these steps to connect to a service and access vector tiles:

  • locate the vector tiles service on the left hand side browser panel. Note that you can also use the top menu and navigate to Layer > Add Layer > Vector Tile Layer

  • right-click to bring up the context menu and choose New Generic connection
  • fill the required values. For URL, use the URL you noted from the previous step, replacing {tileMatrix}/{tileRow}/{tileCol} with {z}/{x}/{y}.
  • press OK to add the service. At this point, if you are using the browser you should see the collection appearing in the menu, below "Vector Tiles"
  • double-click in the collection to add it to the map
  • zoom in to Hyderabad to visualize your dataset

LeafletJS

LeafletJS is a popular JavaScript library to add interactive maps to websites. LeafletJS does not support OGC API's explicitely, however can interact with OGC API by using the results of the API directly.

Add OGC API - Tiles to a website with LeafletJS

  • copy the HTML below to a file called vector-tiles.html, or locate this file in workshop/exercises/html
  • open the file in a web browser

The code uses the LeafletJS library with the leaflet.vectorgrid plugin to display the lakes OGC API - Tiles service on top of an OpenStreetMap base layer.

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<html>
<head><title>OGC API - Tiles exercise</title></head>
<body>
<div id="map" style="width:100vw;height:100vh;"></div>
<link rel="stylesheet" href="https://unpkg.com/leaflet@1.0.3/dist/leaflet.css" />
<script type="text/javascript" src="https://unpkg.com/leaflet@1.3.1/dist/leaflet.js"></script>
<script type="text/javascript" src="https://unpkg.com/leaflet.vectorgrid@1.3.0/dist/Leaflet.VectorGrid.bundled.js"></script>
<script>    
map = L.map('map').setView({ lat: 17.425181, lng: 78.5493906 }, 11);
map.addLayer(
    new L.tileLayer('https://server.arcgisonline.com/ArcGIS/rest/services/NatGeo_World_Map/MapServer/tile/{z}/{y}/{x}', {
    attribution: 'Tiles &copy; Esri &mdash; National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, iPC',
    minZoom: 1,
    maxZoom: 16,
    }));
function getColor(val){
    if (val < 40) {return "#f2e6c7"}
    else if (val < 80) {return "#8fa37e"}
    else if (val < 100) {return "#f0d17d"}
    else if (val < 120) {return  "#d7ded1"}
    else return "#c2d0d9";
}
var vectorTileStyling = {
    greater_hyderabad_municipal_corporation_ward_Boundaries: function(properties) {
        return ({
            fill: true,
            fillColor: getColor(properties.objectid),
            color: "#ffffff",
            fillOpacity: 1.0,
            weight: 5,
            //color: "#ffffff",
            opacity: 1.0,
        });
    }
} 
    var mapVectorTileOptions = {
        rendererFactory: L.canvas.tile,
        interactive: true,
        vectorTileLayerStyles: vectorTileStyling,
        };
    var pbfURL='http://localhost:5000/collections/hyderabad/tiles/WorldCRS84Quad/{z}/{x}/{y}?f=mvt';
    var pbfLayer=L.vectorGrid.protobuf(pbfURL,mapVectorTileOptions).on('click',function(e) {
        console.log(e.layer);
    L.DomEvent.stop(e);
    }).addTo(map); 
</script>
</body>
</html>

Tip

Try adding a different pygeoapi vector tiles layer by updating the code in workshop/exercises/html/vector-tiles.html.

If you want to render the tiles from the Elasticsearch example, you can check out the code from this repository: 

git clone -b ogcapi-ws https://github.com/doublebyte1/vtiles-example.git

Tip

See the official LeafletJS documentation

OpenLayers

OpenLayers is a popular JavaScript library to add interactive maps to websites. OpenLayers natively supports OGC API - Tiles.

Tip

See the official OpenLayers documentation

Summary

Congratulations! You are now able to publish tiles to pygeoapi.