GetMap Requests

A GetMap request is the WMS request you’ll use to fetch a map for use in an SOS dataset. These requests contain a lot of parameters in their queries.

http://neowms.sci.gsfc.nasa.gov/wms/wms?version=1.3.0&service=WMS&REQUEST=GetMap&LAYERS=MODAL2_D_CLD_CI&CRS=CRS:84&FORMAT=image/png&HEIGHT=1800&WIDTH=3600&TRANSPARENT=TRUE&BBOX=-180.0,-90.0,180.0,90.0&STYLES=rgb

version=1.3.0

Specifies the version of the service you’re using. Sometimes parameters and response formats can change from version to version, so services allow you to request a specific version

service=WMS

Identifies this request as a WMS request

REQUEST=GetMap

REQUEST specifies the type of WMS request you’re making. In this case, it’s GetMap

LAYERS=MODAL2_D_CLD_CI

Tells the server which “layer” (which map) to return. This will vary depending on the map service you use, as they all offer different data

CRS=CRS:84

Defines the coordinate reference system. SOS requires CRS:84

FORMAT=image/png

Defines the map’s format. In this case, we’re requesting the map as a PNG (an image format)

HEIGHT=1800

Defines the height of the image in pixels

WIDTH=3600

Defines the widht of the image in pixels

TRANSPARENT=TRUE

Sets the transparency of the map’s backgruond

BBOX=-180.0,-90.0,180.0,90.0

Boundary box setting defines which piece of the map you’re looking at in degrees of latitude and longitude. For a world map, the coordinates shown above will show the complete map. However, the SOS team prefers if users use the parameter <BOUNDING_BOX> to define BBOX, like this: BBOX=<BOUNDING_BOX>. This will always give the full map

STYLES=rgb

Defines the “rendering style of the layer”

If you have an existing GetMap request already, chances are you’ll have to check a few things and change a few others. The three changes that are required, minimum, are below:

1. After the HEIGHT= parameter, change whatever number is there to <IMAGE_HEIGHT>, spelled and capitalized exactly like that
2. After the WIDTH= parameter, change the number to <IMAGE_WIDTH>
3. After the BBOX parameter, change whatever numbers are there to <BOUNDING_BOX>

These changes are required for the SOS system, but they won’t work in a browser, because the keywords such as <IMAGE_HEIGHT> were created by the SOS team, not the designers of WMS.

You should also check a few of the parameters to make sure they’re compatible with the SOS format.

1. CRS should equal CRS:84 or EPSG:4326. This parameter can’t be changed, so if it isn’t correct, you’ll need to find a different WMS server
2. FORMAT should equal image/png, image/jpg, or another SOS-supported image format

If these parameters are correct, you’re good to go! See the How to Display WMS Data on the Sphere section to proceed.