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IDLnetOGCWMS::GetLayers

IDLnetOGCWMS::GetLayers

The IDLnetOGCWMS::GetLayers function method provides access to the layer details that were returned and parsed by the IDLnetOGCWMS::GetCapabilities method. You can return information for all layers or a subset of the layers, which can be useful when:

  • A large number of layers would require significant amounts of memory to return all of them at a single time
  • A user interface needs to display a subset of the available items

Note: Use IDLnetOGCWMS::GetServiceSection to return information related to the service section of the layer information.

Syntax


Result = Obj->[IDLnetOGCWMS::]GetLayers ([, COUNT=variable], [, NUMBER=value] [, INDEX=value])

Return Value


The return value is an array of structures containing one or more layers. Use the COUNT keyword to verify that layers are available since the returned value can be zero when layers are not available. The layer structure contains single values, arrays of strings, and structures.

Layer Structure

The layer structure is complex. Some elements in the main structure return other structures, as shown in the following figure:

Main Layer Structure

The following table contains a list of tags found in the main level Layer structure. All items return string values unless otherwise noted. All tags are valid in versions 1.1.1 and 1.3.0 unless otherwise noted.

Field Name

Description

LAYER

Contains the zero-based layer number as a convenience. Layers are numbered sequentially as they are encountered in the XML file returned by GetCapabilities. This value is generated by IDL.

PARENT

Contains the layer number of the parent of this child level as a convenience. If the layer is at the root level, the value is -1. This value is generated by IDL.

LEVEL

Contains the nesting level of the layer as a convenience. Layers at the root level have a LEVEL value of 1, children of the root level have a value of 2. This value increases with increasing nesting level and is generated by IDL.

VERSION

1.1.1 XML source: <WMT_MS_Capabilities><version>
1.3.0 XML source: <WMS_Capabilities><version>

UPDATE_SEQUENCE

1.1.1 XML source: <WMT_MS_Capabilities><updatesequence>
1.3.0 XML source: <WMS_Capabilities><updatesequence>

NAME

1.1.1, 1.3.0 XML source: <layer><name>

TITLE

1.1.1, 1.3.0 XML source: <layer><title>

ABSTRACT

1.1.1, 1.3.0 XML source: <layer><abstract>

NUM_MAP_FORMAT

Provides the number of map formats as a convenience. This value is generated by IDL.

MAP_FORMAT

Array of strings (0 to many).

1.1.1, 1.3.0 XML source: <capability><request><getmap><format>

NUM_FEATURE_FORMAT

Provides the number of feature formats as a convenience. This value is generated by IDL.

FEATURE_FORMAT

Array of strings (0 to many).

1.1.1, 1.3.0 XML source: <capability><request><getfeatureinfo><format>

NUM_KEYWORD

Provides the number of keywords as a convenience. This value is generated by IDL.

KEYWORD

Array of strings (0 to many).

1.1.1, 1.3.0 XML source: <layer><keywordlist><keyword>

NUM_SRS

Provides the number of SRS elements as a convenience. This value is generated by IDL.

Valid in version 1.1.1 only (version 1.3.0 always returns 0).

SRS

Array of strings (0 to many).

1.1.1 XML source: <layer><srs>

NUM_CRS

Provides the number of CRS elements as a convenience. This value is generated by IDL.

Valid in version 1.3.0 only (version 1.1.1 always returns 0).

CRS

Array of strings (0 to many).

1.3.0 XML source: <layer><crs>

LAT_LON_BBOX

Returns a structure. See Lat_Lon_Bbox Structure for details.

1.1.1 XML source: <layer><latlonboundingbox>

Valid in version 1.1.1 only.

EX_GEOBOX

Returns a structure. See Ex_GeoBox Structure for details.

1.3.0 XML source: <layer><ex_geographicboundingbox>

Valid in version 1.3.0 only.

NUM_BOUNDING_BOX

Provides the number of BOUNDING_BOX elements as a convenience. This value is generated by IDL.

BOUNDING_BOX

Returns an array of structures (0 to many). See Bounding_Box Structure for details.

1.1.1, 1.3.0 XML source: <layer><bounding_box>

NUM_EXTENT

Provides the number of EXTENT elements as a convenience. This value is generated by IDL.

Valid in version 1.1.1 only (version 1.3.0 always returns 0).

EXTENT

Returns an array of structures (0 to many). See Extent Structure for details.

1.1.1 XML source: <layer><extent>

NUM_DIMENSION

Provides the number of DIMENSION elements as a convenience. This value is generated by IDL.

DIMENSION

Returns an array of structures (0 to many). See Dimension Structure for details.

1.1.1, 1.3.0 XML source: <layer><dimension>

ATTRIBUTION

Structure. See Attribution Structure for details.

1.1.1, 1.3.0 XML source: <layer><attribution>

NUM_AUTHORITY

Provides the number of AUTHORITY elements as a convenience. This value is generated by IDL.

AUTHORITY

Returns an array of structures (0 to many). See Authority Structure for details.

1.1.1, 1.3.0 XML source: <layer><authority>

NUM_IDENTIFIER

Provides the number of IDENTIFIER elements as a convenience. This value is generated by IDL.

IDENTIFIER

Returns an array of structures (0 to many). See Identifier Structure for details.

1.1.1, 1.3.0 XML source: <layer><identifier>

NUM_METADATA_URL

Provides the number of METADATA_URL elements as a convenience. This value is generated by IDL.

METADATA_URL

Returns an array of structures (0 to many). See Metadata_URL Structure for details.

1.1.1, 1.3.0 XML source: <layer><metadataurl>

NUM_DATA_URL

Provides the number of DATA_URL elements as a convenience. This value is generated by IDL.

DATA_URL

Returns an array of structures (0 to many). See Data_URL Structure for details.

1.1.1, 1.3.0 XML source: <layer><dataurl>

NUM_FEATURE_URL

Provides the number of FEATURE_URL elements as a convenience. This value is generated by IDL.

FEATURE_URL

Returns an array of structures (0 to many). See Feature_URL Structure for details.

1.1.1, 1.3.0 XML source: <layer><featurelisturl>

NUM_STYLE

Provides the number of STYLE elements as a convenience. This value is generated by IDL.

STYLE

Returns an array of structures (0 to many). See Style Structure for details.

1.1.1, 1.3.0 XML source: <layer><style>

MIN_SCALE

1.1.1 XML source: <layer><scalehint><min>
1.3.0 XML source: <layer><minscaledenominator>

MAX_SCALE

1.1.1 XML source: <layer><scalehint><max>
1.3.0 XML source: <layer><maxscaledenominator>

QUERYABLE

1.1.1, 1.3.0 XML source: <layer><queryable>

CASCADED

1.1.1, 1.3.0 XML source: <layer><cascaded>

OPAQUE

1.1.1, 1.3.0 XML source: <layer><opaque>

NO_SUBSETS

1.1.1, 1.3.0 XML source: <layer><nosubsets>

FIXED_WIDTH

1.1.1, 1.3.0 XML source: <layer><fixedwidth>

FIXED_HEIGHT

1.1.1, 1.3.0 XML source: <layer><fixedheight>

Lat_Lon_Bbox Structure

This child structure is accessed through the LAT_LON_BBOX field of the parent layer structure. All elements are strings unless otherwise noted.

Field

Description

MINX

1.1.1 XML source: <layer><latlonboundingbox><minx>

Valid only in version 1.1.1.

MINY

1.1.1 XML source: <layer><latlonboundingbox><miny>

Valid only in version 1.1.1.

MAXX

1.1.1 XML source: <layer><latlonboundingbox><maxx>

Valid only in version 1.1.1.

MAXY

1.1.1 XML source: <layer><latlonboundingbox><maxy>

Valid only in version 1.1.1.

Ex_GeoBox Structure

This child structure is accessed through the EX_GEOBOX field of the parent layer structure. All elements are strings unless otherwise noted.

Field

Description

WEST

1.3.0 XML source: <layer><ex_geographicboundingbox><westboundlongitude>

Valid only in version 1.3.0.

EAST

1.3.0 XML source: <layer><ex_geographicboundingbox><eastboundlongitude>

Valid only in version 1.3.0.

SOUTH

1.3.0 XML source: <layer><ex_geographicboundingbox><southboundlatitude>

Valid only in version 1.3.0.

NORTH

1.3.0 XML source: <layer><ex_geographicboundingbox><northboundlatitude>

Valid only in version 1.3.0.

Bounding_Box Structure

This child structure is accessed through the BOUNDING_BOX field of the parent layer structure. To determine the number of Bounding_Box structures, access the NUM_BOUNDING_BOX field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

SRS

1.1.1 XML source: <layer><boundingbox><srs>

Valid only in version 1.1.1.

CRS

1.3.0 XML source: <layer><boundingbox><crs>

Valid only in version 1.3.0.

MINX

1.1.1, 1.3.0 XML source: <layer><boundingbox><minx>

MINY

1.1.1, 1.3.0 XML source: <layer><boundingbox><miny>

MAXX

1.1.1, 1.3.0 XML source: <layer><boundingbox><maxx>

MAXY

1.1.1, 1.3.0 XML source: <layer><boundingbox><maxy>

RESX

1.1.1, 1.3.0 XML source: <layer><boundingbox><resx>

RESY

1.1.1, 1.3.0 XML source: <layer><boundingbox><resy>

Extent Structure

This child structure is accessed through the EXTENT field of the parent layer structure. To determine the number of Extent structures, access the NUM_EXTENT field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

NAME

1.1.1 XML source: <layer><extent><name>

Valid only in version 1.1.1.

DEFAULT

1.1.1 XML source: <layer><extent><default>

Valid only in version 1.1.1.

NEAREST_VALUE

1.1.1 XML source: <layer><extent><nearestvalue>

Valid only in version 1.1.1.

EXTENT

1.1.1 XML source: <layer><extent>

Valid only in version 1.1.1.

Dimension Structure

This child structure is accessed through the DIMENSION field of the parent layer structure. To determine the number of Dimension structures, access the NUM_DIMENSION field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

NAME

1.1.1, 1.3.0 XML source: <layer><dimension><name>

UNITS

1.1.1, 1.3.0 XML source: <layer><dimension><units>

UNIT_SYMBOL

1.1.1, 1.3.0 XML source: <layer><dimension><unitsymbol>

DEFAULT

1.3.0 XML source: <layer><dimension><default>

Valid only in version 1.3.0.

MULTIPLE_VALUES

1.3.0 XML source: <layer><dimension><multiplevalues>

Valid only in version 1.3.0.

NEAREST_VALUE

1.3.0 XML source: <layer><dimension><nearestvalue>

Valid only in version 1.3.0.

CURRENT

1.3.0 XML source: <layer><dimension><current>
Valid only in version 1.3.0.

DIMENSION

1.1.1, 1.3.0 XML source: <layer><dimension>

Attribution Structure

This child structure is accessed through the ATTRIBUTION field of the parent layer structure. All elements are strings unless otherwise noted.

Field

Description

TITLE

1.1.1, 1.3.0 XML source: <layer><attribution><title>

ONLINE

1.1.1, 1.3.0 XML source: <layer><attribution><onlineresource>

LOGO_FORMAT

1.1.1, 1.3.0 XML source: <layer><attribution><logourl><format>
 

LOGO_ONLINE

1.1.1, 1.3.0 XML source: <layer><attribution><logourl><onlineresource>

LOGO_WIDTH

1.1.1, 1.3.0 XML source: <layer><attribution><logourl><width>

LOGO_HEIGHT

1.1.1, 1.3.0 XML source: <layer><attribution><logourl><height>

Authority Structure

This child structure is accessed through the AUTHORITY field of the parent layer structure. To determine the number of Authority structures, access the NUM_AUTHORITY field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

NAME

1.1.1, 1.3.0 XML source: <layer><authorityurl><name>

ONLINE

1.1.1, 1.3.0 XML source: <layer><authorityurl><onlineresource>

Identifier Structure

This child structure is accessed through the IDENTIFIER field of the parent layer structure. To determine the number of Identifier structures, access the NUM_IDENTIFIER field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

ID

1.1.1, 1.3.0 XML source: <layer><identifier>

AUTHORITY

1.1.1, 1.3.0 XML source: <layer><identifier><authority>

Metadata_URL Structure

This child structure is accessed through the METADATA_URL field of the parent layer structure. To determine the number of Metadata_URL structures, access the NUM_METADATA_URL field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

TYPE

1.1.1, 1.3.0 XML source: <layer><metadataurl><type>

FORMAT

1.1.1, 1.3.0 XML source: <layer><metadataurl><format>

ONLINE

1.1.1, 1.3.0 XML source: <layer><metadataurl><onlineresource>

Data_URL Structure

This child structure is accessed through the DATA_URL field of the parent layer structure. To determine the number of Data_URL structures, access the NUM_DATA_URL field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

FORMAT

1.1.1, 1.3.0 XML source: <layer><dataurl><format>

ONLINE

1.1.1, 1.3.0 XML source: <layer><dataurl><onlineresource>

Feature_URL Structure

This child structure is accessed through the FEATURE_URL field of the parent layer structure. To determine the number of Feature_URL structures, access the NUM_FEATURE_URL field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

FORMAT

1.1.1, 1.3.0 XML source: <layer><featurelisturl><format>

ONLINE

1.1.1, 1.3.0 XML source: <layer><featurelisturl><onlineresource>

Style Structure

This child structure is accessed through the STYLE field of the parent layer structure. To determine the number of Style structures, access the NUM_STYLE field value. The number of structures can be 0 to many. All elements are strings unless otherwise noted.

Field

Description

NAME

1.1.1, 1.3.0 XML source: <layer><style><name>

TITLE

1.1.1, 1.3.0 XML source: <layer><style><title>

ABSTRACT

1.1.1, 1.3.0 XML source: <layer><style><title>

LEGEND_FORMAT

1.1.1, 1.3.0 XML source: <layer><style><legendurl><format>

LEGEND_ONLINE

1.1.1, 1.3.0 XML source: <layer><style><legendurl><onlineresource>

LEGEND_WIDTH

1.1.1, 1.3.0 XML source: <layer><style><legendurl><width>

LEGEND_HEIGHT

1.1.1, 1.3.0 XML source: <layer><style><legendurl><height>

SHEET_FORMAT

1.1.1, 1.3.0 XML source: <layer><style><stylesheeturl><format>

SHEET_ONLINE

1.1.1, 1.3.0 XML source: <layer><style><stylesheeturl>
<onlineresource>

STYLE_FORMAT

1.1.1, 1.3.0 XML source: <layer><style><styleurl><format>

STYLE_ONLINE

1.1.1, 1.3.0 XML source: <layer><style><styleurl><onlineresource>

Arguments


None

Keywords


COUNT

Set this keyword to a variable that will contain the number of layer structures returned in this method’s structure array. This value can be zero.

NUMBER

Set this keyword to the number of layers to return. If this keyword is not set, all layers will be returned minus the number of those skipped up to the INDEX keyword, if it is set. If this value is zero, zero layers will be returned. If the value is greater than the number of available layers, then this value is ignored and the number of available layers (COUNT) is returned.

Note: When populating a user interface, it is useful to set this keyword equal to the number of rows in the table.

INDEX

Set this keyword to the zero-based index of the first layer to return, skipping over all preceding layers. If this keyword is not set, all layers will be returned. You can use this property to enable navigation through a list of layers displayed in a user interface. For example, suppose there are 10 rows in a table. On the first call to GetLayers, set this value to 0 and NUMBER to 10. To display the next set of values, you would set this keyword to 10 (skip the first 10 values and display the next ten).

Examples


The following code parses the URL of WMS server, queries its capabilities (using GetCapabilities) and then extracts information from the returned XML file using GetLayers and GetServiceSection. Information is printed to the IDL Output Log.

Note: You may need to replace the URL in the following example as there is no guarantee that the given OCG server will be available when you attempt to establish the connection.

FUNCTION ogcwms_callback,  StatusInfo, CallbackData
 
PRINT, StatusInfo
 
; Indicate all is well.
vCancelFlag = 1
RETURN, vCancelFlag
 
END
 
PRO ogc_wms_getlayers_doc
 
; Use the GetLayers method to access data returned in
; the XML file by the GetCapabilities method.
 
; This example queries an OGC server at the following URL. Change
; the value of this variable to access a server of your choice.
url="http://mydataserver.com:80/cgi-bin/mapserv.exe?" + $
   "map=/OGC_Data/WMS/wms_demo.map&service=WMS"
 
; Catch error.
CATCH, errorStatus
IF (errorStatus NE 0) THEN BEGIN
   CATCH,/CANCEL
   PRINT, !ERROR_STATE.MSG
   IF OBJ_VALID(oWms) THEN OBJ_DESTROY, oWms
   RETURN
ENDIF
 
; Create an IDLnetOGCWMS object and parse a known, working URL 
; to set mandatory properties. Use /VERBOSE to show additional 
; information.
oWms = OBJ_NEW("IDLnetOGCWMS", $
   CALLBACK_FUNCTION="ogcwms_callback", /VERBOSE)
oWms->ParseUrl, url
 
; Return and parse a description of all data holdings on
; the WMS server.
count = oWMS->GetCapabilities()
 
; Make sure the server returned some layers.
If (count NE 0) THEN BEGIN
 
   ; Use the GetLayers method to translate the
   ; parsed XML data into an array of IDL structures. The NAME
   ; field of this structure is used to identify what layer 
   ; to request data for from the server.
   layerStruct = oWMS->GetLayers $                          
      (COUNT=layercount, NUMBER=5, INDEX = 1)
   PRINT, "Returning structures for ", + layercount, + " layers"
 
   ; Access elements of the GetLayers structure.
   FOR x=0, layerCount-1 DO BEGIN
      PRINT, 'Layer = ', strtrim(x,2)
      PRINT, '  parent          = ', layerStruct[x].parent
      PRINT, '  level           = ', layerStruct[x].level
      PRINT, '  name            = ', layerStruct[x].name
      PRINT, '  title           = ', layerStruct[x].title
      PRINT, '  version         = ', layerStruct[x].version
      PRINT, '  authority_url   = ', layerStruct[x].authority
      PRINT, '  num styles      =  ', layerStruct[x].num_style
      FOR j=0, layerStruct[x].num_style-1 do begin
        PRINT, '  style name   = ' , layerStruct[x].style[j].name
        PRINT, '  style title  = ' , layerStruct[x].style[j].title
      ENDFOR
   ENDFOR
 
   ; Use the GetServiceSection method to get the Service section
   ; data from the XML file containing the layer info.
   serviceStruct = oWMS->GetServiceSection()
 
   PRINT, 'Service Section'
   PRINT, '  name              = ', serviceStruct.name
   PRINT, '  title             = ', serviceStruct.title
   PRINT, '  abstract          = ', serviceStruct.abstract
   HELP, serviceStruct.keyword
   PRINT, '  keywords          = ', serviceStruct.keyword
   PRINT, '  accessConstraints = ', serviceStruct.access
ENDIF ELSE BEGIN
   void = DIALOG_MESSAGE("No information available " $
      + "from WMS Server", /ERROR)
   RETURN
ENDELSE
 
; Cleanup.
OBJ_DESTROY, oWms
 
END

Tip: Also see Sample WMS Browser.

Version History


6.4

Introduced

See Also


IDLnetOGCWMS::GetCapabilities, IDLnetOGCWMS::GetServiceSection



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