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is there a way to specify pixel tolerance when requesting feature info via GetFeatureInfo WMS request for an ArcGIS Server WMS-published map service? I have not been able to find any such information in the documentation.

The OGC WMS standard does not specify any request parameters for coordinate tolerance, I just wonder if there's similar setting somewhere which could make retrieving feature info a bit more convenient for the user, especially for point features.

Thanks in advance for your help.

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The WMS spec does not provide any direction on how a server should implement the GetFeatureInfo response.

In some systems the "pixel tolerance" is a function of the client (web browser or desktop client) - a clicked point can be buffered and the resulting polygon is sent as the query geometry. However, GetFeatureInfo only accepts a point input so that's a dead end.

However, if you scale down the image size in your GetFeatureInfo request, and also scale down the X and Y coordinate of your query, you can effectively increase the pixel tolerance. Consider the following queries based on the Cities layer for the region surrounding Minneapolis/St.Paul:

WMS GetImage, 400 x 400 pixels

If I issue a GetFeatureInfo request at 138, 145 on a 400x400 map gets me Elk River:

WMS GetFeatureInfo, 138,145, 400x400 - gets results

If I re-issue the request at 140, 140 I get no results:

WMS GetFeatureInfo, 140,140, 400x400 - no results

However, if I halve all values and issue the request at 70,70 on a 200x200 map, it works:

WMS GetFeatureInfo, 70,70, 200x200 - gets results

It's extra work to do this sort of viewport adjustment on-the-fly but should do what you want.

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Sorry but that is absolutely false. The WMS spec defines a particular set of parameters in the query URL. Physical image coordinates in pixels are the input to the GetFeatureInfo method, as well as the information about the original image dimensions and real-world extent. Also, there's no way to specify non-point geometry in GetFeatureInfo operation, so buffering the point also is not an option. –  Petr Krebs Mar 30 '11 at 7:21
    
OK, I'll reword my answer to make more sense. –  mwalker Mar 30 '11 at 16:38
    
mwalker: not the solution I was hoping for, but seems to be as close as you can get. Thanks! –  Petr Krebs Mar 30 '11 at 21:20
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