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IDLnetOGCWMS::GetFeatureInfo

IDLnetOGCWMS::GetFeatureInfo

The IDLnetOGCWMS::GetFeatureInfo function method retrieves a feature information file from a remote OGC WMS server and writes the file to disk. This file contains information about a specific feature. The value of the QUERYABLE tag in the structure returned by IDLnetOGCWMS::GetLayers can be used to determine if the server supports GetFeatureInfo for a particular layer. The OGC WMS server may not offer this support for every layer.

The feature file location is specified by the FEATURE_INFO_FILENAME property, and will be overwritten if this property value remains unchanged between GetFeatureInfo requests.

The URL_PATH and URL_HOSTNAME properties must be set before requesting information from a remote WMS server. You can either set these properties manually or pass a URL to the IDLnetOGCWMS::ParseUrl method prior to making a request. If you are working with a proxy server, you must also set the PROXY_HOSTNAME and PROXY_PORT properties to the correct values.

This method returns only when one of the following occur:

  • Completes retrieval of information from server
  • Encounters an HTTP error
  • Encounters an OGC exception
  • Responds to a cancel request as specified in a callback return value

You can implement a callback to return status information during the request by setting the CALLBACK_FUNCTION property. You can also use a callback to cancel a request. See Using Callbacks with the IDLnetOGCWMS Object for details. This method will throw an error if the GetFeatureInfo request fails.

Syntax


Result = Obj->[IDLnetOGCWMS::]GetFeatureInfo(Feature_Info_Request)

Return Value


The return value is a string containing the path to the file returned by this request or an empty string if no file was returned.

Arguments


Feature_Info_Request

The Feature_Info_Request argument must be a string that contains the required request parameters separated by the & character. These elements can be extracted from the structures returned by the IDLnetOGCWMS::GetLayers method, and many are the same parameters used in the IDLnetOGCWMS::GetMap request. The required elements are shown in the following table, and match those described in the OGC Web Map Service (WMS) specification. See the OGC web site (www.opengeospatial.org) for specification details.

Parameter

Description

SRS=namespace:identifier

Spatial Reference System used in 1.1.1 requests. Required.

Source: The GetMap request parameter, SRS= namespace:identifier.

CRS=namespace:identifier

Spatial Reference System used in 1.3.0 requests. Required.

Source: The GetMap request parameter, CRS= namespace:identifier.

BBOX=minx, miny, maxx, maxy

A coverage subset as defined by the bounding box coordinate pairs defining corners (lower left, upper right), in SRS units. Required.

Source: The GetMap request parameter, BBOX=minx, miny, maxx, maxy.

WIDTH=output_width

Width of map image in pixels. Required.

Source: The GetMap request parameter, WIDTH=output_width.

HEIGHT=output_height

Height of map image in pixels. Required.

Source: The GetMap request parameter, HEIGHT=output_height.

QUERY_LAYERS=layer_list

Comma-separated list of one or more map layers. Required.

Source: Layer names must be one or more of the layer names specified in the LAYERS=layer_list parameter of the IDLnetOGCWMS::GetMap call.

INFO_FORMAT=format

Return format information of feature. Required.

Source: In the Main Layer Structure, see FEATURE_FORMAT.

X=pixel_column

X-coordinate of feature in pixels in map coordinate system. Valid in version 1.1.1 only. Required.

Y=pixel_row

Y-coordinate of feature in pixels in map coordinate system. Valid in version 1.1.1 only. Required.

I=pixel_column

I-coordinate of feature in pixels in map coordinate system. Valid in version 1.3.0 only. Required.

J=pixel_row

J-coordinate of feature in pixels in map coordinate system. Valid in version 1.3.0 only. Required.

FEATURE_COUNT=number

Number of features about which to return information (defaults to 1). Optional

Keywords


None

Examples


See Sample WMS Browser.

Version History


6.4

Introduced

See Also


IDLnetOGCWMS::GetLayers, IDLnetOGCWMS::GetMap



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