[Qgis-developer] QGIS Server and OL3 GetFeatureInfo requests issue

[Mathias Walker]

Hi Giovanni

QGIS Server uses a fixed percentage (1 or 2%) of the image size as a default 
tolerance for GetFeatureInfo requests. This works nicely with a full sized 
image e.g. in the QGIS WebClient. But with the smaller image size in the OL3 
GetFeatureInfo request this results in a single pixel tolerance which requires 
pixel perfect clicks.

There are new parameters in QGIS Server to set the tolerance in GetFeatureInfo 
requests (should be available from QGIS 2.10):

	FI_POINT_TOLERANCE
	FI_LINE_TOLERANCE
	FI_POLYGON_TOLERANCE

The tolerances can be set in pixels per geometry type.

If you add these parameters to your OL3 getGetFeatureInfoUrl() calls, the 
feature info requests should respond to less precise clicks.

Cheers
Mathias

Am Donnerstag, 17. September 2015, 12.07:32 schrieb G. Allegri:

OL3 has changed the way GetFeatureInfo request parameters are generated.
The nre way uses fixed WIDTH/HEIGHT and X/Y (I/J) params: 101 for the first and 
50 latters. Then it builds the BBOX parameter consequently.


The old way they were built from the size and extent of the map, and the query 
coordinate.


The new style makes QGIS Server respond with empty results if the click is not 
exactly on the feature coordinates. 
I've tested the same request on the same layer served by Geoserver, which 
responds even with not so precise clicks.


Can this be caused by coordinates rounding happening inside QGIS Server?


giovanni



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Giovanni Allegri
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