Web Map Service (WMS) General Information
A Web Map Service (WMS) is a standard protocol for serving geo-referenced map images over the Internet that are generated by a map server. The specification was developed and first published by the Open Geospatial Consortium in 1999 (Open Geospatial Consortium).
A WMS server can provide support to temporal requests (WMS-T), this is done by providing a TIME parameter with a time value in the request.
WMS is a way for a client (web browser, GIS application etc.) to request map images from a server. The client sends a request to a map server, then the map server generates an image based on parameters passed to the server in the request and the server returns an image.
The WMS server generates an image from whatever source material, which could be vector data, raster data, or a combination of the two
Type of WMS Requests
There are a number of WMS requests that can be made. Here is a list of some of the most useful.
WMS GetCapabilities
This requests information on the WMS server itself, returned as the 'capabilities document'.
The capabilities document is an XML response that details the supported image formats, projections, and map layers being served by that WMS.
WMS GetMap
A GetMap request retrieves a map from a WMS site. GetMap allows the client to specify a set of parameters as distinct layers, the spatial reference system, the geographic area, and other parameters describing the returned map format.
Upon receiving the GetMap request, a WMS site will either satisfy the request or send an error message in accordance with the exception instructions contained in the GetMap request.
The tables below list some of the parameters that can be requested for a GetMap for EFAS and GLoFAS.
| EFAS GetMap Parameters | ||
| Parameter | Example value | Comment |
|---|---|---|
| Version | 1.1.1 | WMS version. Default is 1.3.0 |
| Request | GetMap | Name of request |
| Layers | Countries, Catchments | List of layers requested in the service |
| CRS | EPSG:4326 | Spatial reference value. This example uses geographic WGS 1984 |
| BBOX | -124.21,-66.49 | Bounding box in spatial reference system coordinates of the map. In this example, the coordinates are in decimal degrees. |
| Width | 600 | Width in pixels of the returned image |
| Height | 400 | Height in pixels of the returned image |
| Format | image/png | Image file format |
| Example of a GetMap Request for EFAS | ||
REQUEST=GetMap&SERVICE=WMS&VERSION=1.3.0&LAYERS=Countries,Catchments&FORMAT=image/png&STYLES=&CRS=EPSG:3857 &BBOX=-5009377.085,2817774.6103125,4070118.8815625003,11897270.576875&WIDTH=600&HEIGHT=600 | ||
GloFAS GetMap Parameters | ||
| Parameter | Example value | Comment |
|---|---|---|
| Version | 1.3.0 | WMS version. Default is 1.3.0 |
| Request | GetMap | Name of request |
| Layers | AccRain | List of layers requested in the service |
| CRS | EPSG:4326 | Spatial reference value. This example uses geographic WGS 1984 |
| BBOX | 23.07970000000000255,-44.29690000000000083,73. 77580000000000382,76.99219999999999686 | Bounding box in spatial reference system coordinates of the map. In this example, the coordinates are in decimal degrees. |
| Width | 1439 | Width in pixels of the returned image |
| Height | 602 | Height in pixels of the returned image |
| Format | image/png | Image file format |
| Example of a GetMap Request for GloFAS | ||
https://ows.globalfloods.eu/glofas-ows/ows.py?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=23.07970000000000255,-44.29690000000000083,73. 77580000000000382,76.99219999999999686&CRS=EPSG:4326&WIDTH=1439&HEIGHT= 602&LAYERS=AccRainEGE&STYLES=&FORMAT=image/png&DPI=96&MAP_RESOLUTION=96& FORMAT_OPTIONS=dpi:96&TRANSPARENT=TRUE | ||
WMS GetFeatureInfo
GetFeatureInfo retrieves feature information by identifying a point on a map based on its pixel location. The GetFeatureInfo request embeds many of the parameters required in the GetMap request along with parameters specific to querying layers.
In the OGC WMS specification, GetFeatureInfo is optional. The specification leaves the response format open, and there is no standard.
Credentials for accessing CEMS-Flood WMS-T (Web Map Service Time)
CEMS-Flood WMS-T gives access to the CEMS-Flood layers in a GIS environment or via a web browser. Is it possible to access the WMS layers using any WMS client viewer, such as Quantum GIS (QGIS) or ESRI ArcMap.
The EFAS WMS-T is freely accessible for non authenticated users but those users have access to a limited number of layers and non real-time forecasts (only forecasts older than 30 days). EFAS partners users can access real time forecasts and all the available EFAS layers (depending on their access credentials - see section below for details on access).
For GloFAS WMS-T access, no credentials are needed as GloFAS is open source.
How to access the EFAS WMS-T
For EFAS users:
You need to retrieve your WMS access token through the web-interface as follows (this is a one time only operation):
- Log-in into https://www.efas.eu
- Navigate to the EFAS Web Services page (https://www.efas.eu/efas-web-services)
- In the service type table, copy the url address for the EFAS WMS together with your access token i.e. https://www.efas.eu/api/wms/?token=[your_personal_access_token]
- DO NOT share your personal token with anybody
- Follow the instructions on accessing CEMS-Flood WMS via web browser
NON EFAS users:
- Navigate to the EFAS Web Services page (https://www.efas.eu/efas-web-services)
- In the service type table copy the url address for the EFAS WMS
- Follow the instructions on accessing CEMS-Flood WMS via web browser