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 (https://www.ogc.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