Exercise 4 - Maps of geospatial data via OGC API - Maps¶

OGC API - Maps provides a Web API to access any geospatial data as a georeferenced map image.

• OGC API - Maps

Here are a few things that a client can request from a OGC API - Maps server:

• Request a visual representation of one or more geospatial data layers in different styles;
• Select by area, time and resolution of interest;
• Change parameters such as the width, height and coordinate reference systems.

pygeoapi support¶

pygeoapi supports the OGC API - Maps specification, using MapServer MapScript and a WMS facade as core backends.

Publish a vector dataset¶

In this section we'll be exposing a Geopackage file available at workshop/exercises/data/airport.gpkg location using MapServer MapScript. This data can be consumed with various clients which are compliant with OGC APIs - Maps. List of few such clients can be found here. Here we can also pass style in .sld format. Which can be generated on Geoserver, QGIS, etc.

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airports:
    type: collection
    title: airports of the world
    description: Point data representing airports around the world with various metadata such as name, Code, etc.
    keywords:
        - airports
        - natural earth
    links:
        - type: text/html
          rel: canonical
          title: information
          href: https://www.naturalearthdata.com/downloads/10m-cultural-vectors/airports/
          hreflang: en-US
    extents:
        spatial:
            bbox: [-180,-90,180,90]
            crs: http://www.opengis.net/def/crs/OGC/1.3/CRS84
        temporal:
            begin:
            end: null  # or empty
    providers:
        - type: map
          name: MapScript
          data: /data/airport.gpkg
          options:
              type: MS_LAYER_POINT
              layer: airport
              style: /data/airport.sld
          format:
              name: png
              mimetype: image/png
        - type: feature
          name: SQLiteGPKG
          data: /data/airport.gpkg
          id_field: fid
          table: airport

After the server has started you can access the collection page here:

http://localhost:5000/collections/airports

And the map here:

http://localhost:5000/collections/airports/map?f=png

The map comes with the default CRS84 CRS, but you can easily change it with the crs parameter:

http://localhost:5000/collections/airports/map?f=png&crs=EPSG:3857

You can also adjust other parameters (such as bounding box (bbox), bounding box CRS (bbox-crs), as well as width and height to create custom maps:

http://localhost:5000/collections/airports/map?f=png&bbox-crs=OGC:CRS84&bbox=-142,42,-52,84

http://localhost:5000/collections/airports/map?f=png&width=400&height=400

Note

OGC API - Maps supports CRS from Compact URIs (CURIEs, i.e. EPSG:4326, CRS84), safe CURIEs (e.g.: [EPSG:4326], [CRS84]) and URIs:

http://localhost:5000/collections/airports/map?f=png&crs=https://www.opengis.net/def/crs/EPSG/0/3857

http://localhost:5000/collections/airports/map?f=png&crs=https://www.opengis.net/def/crs/EPSG/0/3395

EPSG:4326	EPSG:3857	EPSG:3395

You can read more about the different ways of expressing CRSs on the maps section of the pygeoapi documentation.

OPTIONAL: pygeoapi as a WMS proxy¶

You can check the "pygeoapi as a Bridge to Other Services" section to learn how to publish WMS as OGC API - Maps.

Client access¶

QGIS¶

QGIS added support for API's providing rendered image layers via its raster support.

OWSLib¶

OWSLib is a Python library to interact with OGC Web Services and supports a number of OGC APIs including OGC API - Maps.

pip3 install owslib

pip3 install owslib

>>> from owslib.ogcapi.maps import Maps
>>> m = Maps('http://localhost:5000')
>>> data = m.map('airports', width=1200, height=800, transparent=False)
>>> with open("output.png", "wb") as fh:
...     fh.write(data.getbuffer())

>>> from owslib.ogcapi.maps import Maps
>>> m = Maps('http://localhost:5000')
>>> data = m.map('airports', width=1200, height=800, transparent=False)
>>> with open("output.png", "wb") as fh:
...     fh.write(data.getbuffer())

Summary¶

Congratulations! You are now able to serve an OGC WMS via pygeoapi and OGC API - Maps.