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Copyright © 2006 Open Geospatial Consortium, Inc. All Rights Reserved.
A WMS shall render the requested layers by drawing the leftmost in the list bottommost, the next one over that, and so on.
The optional LayerLimit element in the service metadata is a positive integer indicating the maximum number of layers a client is permitted to include in a single GetMap request. If this element is absent, the server imposes no
limit.
7.3.3.4 STYLES
The mandatory STYLES parameter lists the style in which each layer is to be rendered. The value of the STYLES parameter is a comma-separated list of one or more valid style names. There is a one-to-one correspondence
between the values in the LAYERS parameter and the values in the STYLES parameter. Each map in the list of LAYERS is drawn using the corresponding style in the same position in the list of STYLES. Each style Name shall
be one that was defined in a StyleName element that is either directly contained within, or inherited by, the associated Layer element in service metadata. In other words, the client may not request a Layer in a Style
that was only defined for a different Layer. A server shall throw a service exception code = StyleNotDefined if an unadvertised Style is requested. A client may request the default Style using a null value as in “STYLES=”. If
several layers are requested with a mixture of named and default styles, the STYLES parameter shall include null values between commas as in “STYLES=style1,,style2,,”. If all layers are to be shown using the default style,
either the form “STYLES=” or “STYLES=,,,” is valid.
If the server advertises several styles for a layer, and the client sends a request for the default style, the choice of which style to use as default is at the discretion of the server. The ordering of styles in the service metadata does
not indicate which is the default.
7.3.3.5 CRS
The CRS request parameter states what Layer CRS see 6.7.3 applies to the BBOX request parameter. The value of the CRS parameter in a request to a particular server shall be one of the values defined in that server’s
service metadata in a CRS element defined or inherited by the requested layer. The same CRS applies to all layers in a single request.
A WMS server is not required to support all possible CRSs, but it shall advertise in its service metadata those CRSs which it does offer and shall accept requests for all advertised CRSs. If a request contains a CRS not
offered by a particular server, the server shall throw a service exception code = “InvalidCRS”.
Clients are not required to support all possible CRSs. If a client and server do not support any mutually agreeable CRSs, the client may, at its discretion, cease communicating with that server, or search for an intermediary
service provider that performs coordinate transformations, or allow the user to choose other disposition methods.
This International Standard does not define a facility for clients to explicitly request reprojection or coordinate transformation. That is, only a single CRS request parameter is defined, so it is not possible to specify a source
CRS for selecting geographic information and a different target CRS for the portrayal output. Reprojection may occur implicitly, however, if the server offers multiple CRSs but internally stores its geographic information in a
particular CRS.
If the WMS server has declared CRS=CRS:1 for a Layer, as discussed in 6.7.3.5, then the Layer does not have a well-defined coordinate reference system and should not be shown in conjunction with other layers. The client
shall specify CRS=CRS:1 in the GetMap request and the server may issue a service exception otherwise. When this CRS is used in the request, the BBOX parameter units shall be pixels.
Copyright © 2006 Open Geospatial Consortium, Inc. All Rights Reserved.
35 7.3.3.6 BBOX
The mandatory BBOX parameter allows a client to request a particular Bounding Box. Bounding Boxes are defined in 6.7.4. The value of the BBOX parameter in a GetMap request is a list of comma-separated real
numbers see 6.5 in the form minx,miny,maxx,maxy
. These values specify the minimum X, minimum Y, maximum X, and maximum Y values of a region in the Layer CRS of the request. The units, ordering and direction
of increment of the x and y axes are as defined by the Layer CRS see 6.7.3 The four bounding box values indicate the outside limits of the region. The relation of the Bounding Box to the map pixel matrix is that the
bounding box goes around the “outside” of the pixels of the map rather than through the centres of the map’s border pixels. In this context, individual pixels represent an area on the ground.
If a request contains an invalid BBOX e.g. one whose minimum X is greater than or equal to the maximum X, or whose minimum Y is greater than or equal to the maximum Y the server shall throw a service exception.
If a request contains a BBOX whose area does not overlap at all with the BoundingBox element in the service metadata for the requested layer, the server shall return empty content that is, a blank map or an graphic
element file with no elements for that map. Any features that are partly or entirely contained in the Bounding Box shall be returned in the appropriate format.
If the Bounding Box values are not defined for the given CRS e.g. latitudes greater than 90 degrees in CRS:84, the server should return empty content for areas outside the valid range of the CRS.
If the WMS server has declared that a Layer is not subsettable, as described in 7.2.4.7.5, then the client shall specify exactly the declared Bounding Box values in the GetMap request and the server may issue a service
exception otherwise.
7.3.3.7 FORMAT
