DescribeCoverage Operation |
The DescribeCoverage action is a required action.
The DescribeCoverage operation allows a client to request a full description of one or more raster layers of a WCS service. The server returns a description of the requested XML document for the Coverage layer detailed information.
The client should send a Get request encoded in KVP.
The main request parameters of DescribeCoverage operation are shown in the following table:
Table 1 Main Parameters of DescribeCoverage Operation Request
| Request parameters | Whether it is required | Description |
| SERVICE=WCS |
Yes |
Service type Request WCS service. The request type needs to be set to " WCS ". |
| REQUEST=DescribeCoverage |
Yes |
Request name Request DescribeCoverage operation, the request name needs to be set to 'DescribeCoverage'. |
|
Version |
Yes |
The version of the requested WCS service. |
|
Identifiers |
Yes |
Specify the layer to request. identifiers=identifier1, identifier2,…… |
Note: The case of the parameters is not required, and the order of the request parameters can also be arranged in any order.
DescribeCoverage operations are requested as follows:
<ServiceRoot>?SERVICE=WCS&REQUEST=DescribeCoverage&Version=1.1.2&Identifiers=*,*
ServiceRoot is the URI root directory of the service. Please refer to URI Settings .
FFor example, after the local iServer service is started, the XML document returned by the GetCapabilities request to the data-world/wcs112 service introduces the relevant information of the current service and the Coverage layer information available in the service. Please refer to the GetCapabilities operation for details. From this, it can be seen that data-world/wcs112 provides two available Coverage layers, with Identifiers 1 and 2 respectively. In this example, we request Identifier=1, that is Day@World The detailed information and request URI are as follows:
http://localhost:8090/iserver/services/data-world/wcs112?SERVICE=WCS&REQUEST=DescribeCoverage&Version=1.1.2&Identifiers= 1
See the Response example for the returned response results.
The server will return an XML document describing the detailed information of each requested Coverage data, that is, each Coverage CoverageDescription.
CoverageDes cription contains the following key elements:
Table 2 Contents returned by Describe Coverage Operation
| Element name | Whether it is required | Description |
| (Description) |
Yes |
Description of Coverage. |
|
Identifier |
Yes |
Unique identification of the current Coverage. |
|
Metadata |
No |
More information on current Coverage. |
|
Domain |
Yes |
The available space-time extent of the current Coverage. See Domain for details. |
|
Range |
Yes |
The range of the current Coverage value. See Range for details. |
|
SupportedCRS |
Yes |
A coordinate reference system that supports the data returned by the Get Coverage operation. |
|
SupportedFormat |
Yes |
Supports the format of the data returned by the Get Coverage operation. Such as GeoTIFF, HDF-EOS, NITF, CF-NetCDF Etc. |
Domain is divided into SpatialDomain (spatial domain, required parameter) and TemporalDomain (time domain, optional parameter). The former represents the spatial range of the current coverage, while the latter represents the time point sequence or time interval sequence of the current coverage.
The main labels of SpatialDomain are shown in Table 3.
TemporalDomain is mainly composed of Timestamp sequence, which is determined by TimePositionOrInterval, that is, TimePosition and TimePeriod ultimately determine the time domain. The parameters for defining TimePeriod are shown in Table 4.
Table 3 Main Contents of SpatialDomain
| Element name | Whether it is required | Description |
|
BoundingBox |
Yes |
The bounding box of the current layer. |
|
GridCRS |
No |
The coordinate reference system of the current Coverage. |
|
Transformation |
No |
Current Coverage If projection conversion is required, use this projection conversion method. |
|
ImageCRS |
No |
If the current Coverage does not have GridCRS, you need to use ImageCRS. |
|
Polygon |
No |
The polygon that describes the Domain of the current Coverage. |
Table 4 Parameters of TimePeriod
| Element name | Whether it is required | Description |
|
BeginTime |
Yes |
Start time of the current segment. |
|
EndTime |
Yes |
The end time of the current segment. |
|
TimeResolution |
No |
Time resolution. |
|
frame |
No |
Time frame of reference. |
The range of values in Range is mainly described by Field (required parameter). For example, for grid elevation data or temperature data, this parameter can be used to describe the elevation range or temperature range that can be returned. And Field is a description of a Range in terms of scalar-valued or vector-valued and contains the following parameters:
Table 5 Main Parameters of the Field
| Element name | Whether it is required | Description |
| (Description) |
Yes |
A brief description of the current scope. |
|
Identifier |
Yes |
Unique identification of the current scope. |
|
Definition |
Yes |
More definition information for the current scope, including meaning, units, etc. |
|
NullValue |
No |
If there are no legal range values, this parameter is used. |
|
InterpolationMethods |
Yes |
Difference value method, the difference value method supported by the server for the available value range (Field) of current Coverage. |
|
Axis |
No |
The control variables of the vector range, i.e., the coordinate axis scale values, are detailed in Table 6. |
Table 6 Main Parameters of Axis
| Element name | Whether it is required | Description |
| (Description) |
Yes |
Brief description of Axis. |
|
Identifier |
Yes |
Unique identification of the current Axis. |
|
AvailableKeys |
Yes |
List of Key values for the current Axis. Contains the child element Key, which is used to represent a key value. |
|
Meaning |
No |
The meaning or significance of the current Axis value. |
|
DataType |
No |
Current Axis value data type. |
|
ValuesUnit |
No |
If necessary, the unit reference system of the current Axis value is provided through this parameter. |
|
Metadata |
No |
Complementary to these numerical domain meta-information. |
Request for the data world/wcs102 service in the example Day@World After executing the DescribeCoverage request on the image data, the XML document returned by the server is as follows: