DescribeCoverage Operation |
A DescribeCoverage operation is a necessary operation.
The DescribeCoverage operation allows a client to request a full description of one or more grid layers of that WCS. The server responds to such a request with an XML document describing one or more Coverages.
WCS clients may implement Get request using KVP encoding.
The main parameters of DescribeCoverage operation request are shown in the following table:
Table 1 Parameters in DescribeCoverage operation request
| Request parameters | O/M | Description |
| SERVICE=WCS |
Mandatory |
Service type. Request WCS service. Shall be "WCS". |
| REQUEST=DescribeCoverage |
Mandatory |
Request names. Request name. Shall be "DescribeCoverage". |
|
Version |
Mandatory |
Specification version for operation. |
|
Identifiers |
Mandatory |
Specifies the request layer. identifiers=identifier1, identifier2,…… |
Note: The case of the parameters is not important and the order of the request parameters can be random.
DescribeCoverage operation are as follows:
<ServiceRoot>?SERVICE=WCS&REQUEST=DescribeCoverage&Version=1.1.2&Identifiers=*,*
ServiceRoot is the URI root directory of service and refer to the URI setting of service.
After started the iServer service, the XML document that is returned by GetCapabilities request introduces the current service information and the available Coverage layer information in the data-world/wcs112 service. Please refer to GetCapabilities Operation for more details. It follows that data-world/wcs112 provides two available Coverage layers and the Identifier is 1, 2. The example will set request Identifier=1, namely the detailed information of Day@World, and the request URI is shown in the following:
http://localhost:8090/iserver/services/data-world/wcs112?SERVICE=WCS&REQUEST=DescribeCoverage&Version=1.1.2&Identifiers=1
The returned response result seeResponse example.
The service will return the XML document of every Coverage data that describes request, namely the CoverageDescription of every Coverage.
CoverageDescription contains the following contents:
Table 2 The contents of DescribeCoverage operation returned
| Element Name | O/M | Description |
| (Description) |
Mandatory |
Description of a coverage. |
|
Identifier |
Mandatory |
Unambiguous identifier of this coverage, unique for this WCS server. |
|
Metadata |
Optional |
More metadata about this coverage. |
|
Domain |
Mandatory |
Available coverage locations in space and/or time. See also Domain. |
|
Range |
Mandatory |
Available coverage values. See also Range. |
|
SupportedCRS |
Mandatory |
Coordinate reference system of data that support GetCoverage operation return. |
|
SupportedFormat |
Mandatory |
Identifier of format in which GetCoverage operation response can be encoded. Such as GeoTIFF, HDF-EOS, NITF, CF-NetCDF etc. |
Domain consists of SpatialDomain and TemporalDomain. The former is definition of spatial domain of this coverage and a required parameter. The latter is definition of temporal domain of this coverage and optional parameter.
The main labels of SpatialDomain are shown in the following Table 3.
TemporalDomain is mainly composed of TimeSequence and TimeSequence is decided by TimePositionOrInterval, namely TimePosition and TimePeriod finally decide the temporal domain. Specifies the parameters of TimePeriod, see Table 4.
Table The main contents of SpatialDomain
| Element Name | O/M | Description |
|
BoundingBox |
Mandatory |
The bounding box of the current layer. |
|
GridCRS |
Optional |
The reference coordinate system of current Coverage. |
|
Transformation |
Optional |
Georeferencing coordinate transformation for unrectified coverage. |
|
ImageCRS |
Optional |
If the current coverage does not have GridCRS, the ImageCRS must be used. |
|
Polygon |
Optional |
The Domain polygon that describes the current coverage. |
Table 4 Parameters of TimePeriod
| Element Name | O/M | Description |
|
BeginTime |
Mandatory |
Start of this time period. |
|
EndTime |
Mandatory |
End of this time period. |
|
TimeResolution |
Optional |
Temporal resolution. |
|
frame |
Optional |
Temporal reference system. |
The range of values in the Range is mainly described by Field (required parameter). For example, for grid or temperature data it will describe the temperature and grid range of returned data with this parameter. Description of a field in range records, either scalar-valued or vector-valued. Contains the following parameters:
Table 5 Parameters in Field
| Element Name | O/M | Description |
| (Description) |
Mandatory |
Description of this field. |
|
Identifier |
Mandatory |
Identifier of this field,unique for this coverage. |
|
Definition |
Mandatory |
Further definition of this field, including meaning, units, etc. |
|
NullValue |
Optional |
Value used when valid range values are not available. |
|
InterpolationMethods |
Mandatory |
Spatial interpolation method(s) that server can apply to this field. |
|
Axis |
Optional |
The axis scale value, see Table 6. |
Table 6 Parameters of Axis.
| Element Name | O/M | Description |
| (Description) |
Mandatory |
Description of Axis. |
|
Identifier |
Mandatory |
Identifier of this axis, unique for this field. |
|
AvailableKeys |
Mandatory |
List of values of keys for this axis. Contain child element Key and used to express the key value. |
|
Meaning |
Optional |
Reference to meaning or semantics of this value or set of values. |
|
DataType |
Optional |
Reference to the data type of this set of values. |
|
ValuesUnit |
Optional |
Indicates that this quantity has units or reference system, and provides the value used. |
|
Metadata |
Optional |
Additional metadata about domain of this quantity. |
The server will return XML document as following if Day@World image data performed DescribeCoverage request of the data-world/wcs112 service in the Request example