[mapserver-dev] WMS exception for requests width height=1

Worth Lutz wal3 at mindspring.com
Wed Apr 10 12:00:38 PDT 2013

If I understand correctly, it is because MapServer is based upon a cell size
of center of pixel to center of pixel.


With 1 pixel you have nothing. With 2 pixels you have 1 cell.


Worth Lutz


From: mapserver-dev-bounces at lists.osgeo.org
[mailto:mapserver-dev-bounces at lists.osgeo.org] On Behalf Of Martin Kofahl
Sent: Wednesday, April 10, 2013 2:40 PM
To: MapServer Dev Mailing List
Subject: [mapserver-dev] WMS exception for requests width height=1



currently, I see wms clients (qgis, arcgis 10) doing getmap requests with
height=1. MapServer (6.2) throws an exception: 


msDrawMap(): Image handling error. Unable to initialize image.

msCalculateScale(): General error message. Invalid image extent, minx=nan,
miny=nan, maxx=nan, maxy=nan.


The reason is in msAdjustExtent(), where the cell size is calculated using
MS_CELLSIZE(miny,maxy,height), defined as ((max - min)/(d-1)). Formally, I
don't see any reasons against 1 pixel requests. What are the reasons for




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