Web Map Service (WMS)

NCI’s GSKY Data Server supports the Open Geospatial Consortium (OGC) Web Map Service (WMS), which is a standard protocol for serving geospatial data as images (e.g., PNG).

Constructing WMS Requests

To request a spatial subset of data through GSKY using WMS, a GetMap URL defining the subset has to be constructed. This URL can be used within a web browser to communicate to the GSKY Data Server, which will return the requested map image of the subset.

For example, the GetMap request takes the following form:

http://gsky.nci.org.au/ows/dea?service=WMS&version=1.3.0&request=GetMap&layers=value&crs=value &styles=value &format=value &bbox=value&width=value &height=value &colorscalerange=value &transparent=value&time=value&Styles=value

where red indicates required fields, blue are optional, and green are where input values relevant to the dataset and user request need to be defined.

GetMap parameters:

Parameter Required/Optional Input
service Required WMS
version Required 1.1.1 **, 1.3.0 (default)
request Required GetMap
layers Required <variable>
crs Required <crs_value>
format Required image/png, image/png;mode=32bit, image/gif, image/jpeg
bbox Required <ymin,xmin,ymax,xmax>
width Required Image width in pixels
height Required Image height in pixels
colorscalerange Optional <min,max>
transparent Optional True, False
time Optional <time_value>
Styles Optional <style_name>

** Syntax differences for v1.1.1 GetMap requests:

  • Use src in place of crs
  • The order of bbox values are: <xmin,ymin,xmax,ymax>

WMS GetCapabilities request

Where do you find valid input values?

In order to contruct the GetMap URL, a GetCapabilities request can be made to the server. This requests returns an xml describing the available WMS parameters (metadata, services, and data) made available by NCI’s GSKY server.

GetCapabilities example:

../_images/gsky_wms1.png

WMS GetMap request

Using the information returned from a GetCapabilities request, a GetMap URL can be constructed and then entered into the address bar of any web browser.

Example GetMap request:

service=WMS&
layers=landsat8_nbart_16day&
crs=EPSG:4326&
format=image/png&
request=GetMap&
height=512&
width =512&
version=1.3.0&
bbox=-37,147,-35,148&
time=2013-04-20T00:00:00.000Z&
transparent=FALSE&
Styles=tc

http://gsky.nci.org.au/ows/dea?service=WMS&layers=landsat8_nbart_16day&crs=EPSG:4326&format=image/png &request=GetMap&height=512&width=512&version=1.3.0&bbox=-37,147,-35,148 &time=2013-04-20T00:00:00.000Z&transparent=FALSE&Styles=tc

If the URL is correctly formed, the requested map will be displayed.

../_images/gsky_wms2a.png