WMS GetFeatureInfo access

The GetFeatureInfo operation (optional) returns information about features near the specified point on the map. Allows users to click on a pixel to query a feature's schema and metadata.

GetFeatureInfo is an optional operation. This operation is only supported for layers with the attribute queryable="1" (true). If a WMS client makes a request to a layer that does not support this operation, a formatted service exception will be returned.

TA WMS may provide the optional GetFeatureInfo operation, and a WMS that provides this operation calls its map "queryable". The client can add a position parameter (such as (X, Y) value, that is, the offset from the upper left corner of the picture) or the number of elements that need to query information near the point, to the URL of the requested map, information about the corresponding feature on the map can now be requested.

Since WMS is stateless, the GetFeatureInfo request should also include all the parameters in the original GetMap request (except Version and Request). Based on the spatial context information (BBOX, SRS, Width and Height) in the GetMap request and the (X, Y) location selected by the user, the WMS returns more information about that location.

Also included in the GetFeatureInfo request parameter is the Query_Layers parameter, which specifies the layers from which feature information is obtained. The layers in this parameter list must be those contained in the WMS Capabilities XML document.

The optional Info_Format parameter in the GetFeatureInfo request specifies the format in which the feature's information is returned. The format is defined as a MIME type in the WMS Capabilities XML document. Such as Info_Format=application/vnd.ogc.gml table does not return results described in GML.

The optional Feature_Count parameter in the GetFeatureInfo request indicates the maximum number of features to return feature information. The default value is 1 . The X,Y parameters represent the pixel coordinates of the point of interest on the map. The X,Y values are within the Width and Height parameter values, respectively. The origin of the coordinates is in the upper left corner of the picture.

If GetFeatureInfo request is valid, WMS will respond according to Info_Format. The nature of the response will be at the discretion of the WMS server, but generally corresponds to the closest element to the point (X,Y).

GetFeatureInfo request using WMS service in MapServer

This describes the GetFeatureInfo access to the published MapServer WMS service.

The first is Mapfile:

01 MAP
02     NAME "EX2_"
03     IMAGETYPE "png24"
04     EXTENT -180 -90 180 90
05     SIZE 600 300
06     SHAPEPATH "/gdata"
07     SYMBOLSET "../symbols/symbols35.sym"
08     FONTSET "../fonts/fonts.list"
09     OUTPUTFORMAT
10         NAME "png"
11         DRIVER "AGG/PNG"
12         MIMETYPE "image/png"
13         IMAGEMODE RGB
14         EXTENSION "png"
15         FORMATOPTION "GAMMA=0.75"
16     END
17     WEB
18         TEMPLATE "tmpl_ogc.html"
19         IMAGEPATH "/owg/ms_tmp/"
20         IMAGEURL "/ms_tmp/"
21         METADATA
22             "wms_title" "WMS Demo Server"
23             "wms_version" "1.3.0"
24             "wms_onlineresource" "http://webgis.pub/cgi-bin/mapserv?map=/owg/mfb2.map&"
25             "wms_srs" "EPSG:4326"
26             "wms_enable_request" "*"
27             "ows_enable_request" "*"
28             "wms_feature_info_mime_type" "text/html"
29             "wms_format" "image/png"
30         END
31     END
32     PROJECTION
33         "init=epsg:4326"
34     END
35     LAYER
36         NAME "topo"
37         DATA "land_shallow_topo_8192.tif"
38         STATUS OFF
39         TYPE RASTER
40         PROCESSING "BANDS=1,2,3"
41         PROJECTION
42             "init=epsg:4326"
43         END
44     END
45     LAYER
46         NAME "states"
47         DATA "wcountry.shp"
48         STATUS OFF
49         TYPE POLYGON
50         TEMPLATE "tmpl_ogc.html"
51         METADATA
52             "wms_title" "test2"
53             "wms_version" "1.3.0"
54             "wms_srs" "EPSG:4326 EPSG:3857"
55             "wms_enable_request" "*"
56             "ows_enable_request" "*"
57             "wms_feature_info_mime_type" "text/html"
58             "wms_format" "image/png"
59         END
60         PROJECTION
61             "init=epsg:4326"
62         END
63         CLASS
64             NAME "States"
65             STYLE
66                 COLOR 232 232 232
67                 OUTLINECOLOR 32 32 32
68             END
69         END
70     END
71     LAYER
72         NAME "states_line"
73         DATA "wcountry.shp"
74         STATUS OFF
75         TYPE LINE
76         TEMPLATE "tmpl_ogc.html"
77         METADATA
78             "wms_title" "test3"
79             "wms_version" "1.3.0"
80             "wms_srs" "EPSG:4326 EPSG:3857"
81             "wms_enable_request" "*"
82             "ows_enable_request" "*"
83             "wms_feature_info_mime_type" "text/html"
84             "wms_format" "image/png"
85         END
86         PROJECTION
87             "init=epsg:4326"
88         END
89         CLASS
90             NAME "State Boundary"
91             STYLE
92                 COLOR 132 132 32
93             END
94         END
95     END
96 END

Compared to the previous mfb1.map:

This Mapfile is configured with the WMS service. View function:

Open a link

View the map

Access using GetFeatureInfo

Use GetFeatureInfo

The above results are output using a template.

Note

WMS, Web Mapping Server, is a specification published by OGC.

GetFeatureInfo is an access method supported by WMS.