[BUG] WCS Error?

[Ben Tuttle]

This has been added to bugzilla:
http://mapserver.gis.umn.edu/bugs/show_bug.cgi?id=1983


On 12/7/06, Frank Warmerdam <warmerdam at pobox.com> wrote:
> Ben Tuttle wrote:
> > Hi all-
> > I have two questions related to mapserver and WCS. First, I am running
> > mapserver 4.10.0 on linux. I am trying to set up WCS access to global
> > 30 arcsec data sets.
> > Question 1:
> >  It seems that mapserver does not respect resx and resy. Example: if
> > I make the following request
> > http://www.ngdc.noaa.gov/eog/maps/test5.php?SERVICE=WCS&REQUEST=GetCoverage&Coverage=vis_mosaic&STYLES=&CRS=EPSG:4326&BBOX=-125,30,-115,40&resx=0.00833333&resy=0.00833333&Format=geotiff
> >
> > the data comes back as  0.00834028,-0.00834028 instead of
> > 0.00833333,-0.00833333 (the native resolution of the data is
> > 0.00833333,-0.00833333). Additionally the given bounding box actually
> > covers an area 1201px by 1201px in the data. However, the returned
> > image is 1200px by 1200px. If compared to the original data one can
> > see that mapserver has resampled the returned image to fit the area
> > which is 1201 by 1201 into an image that is 1200 by 1200, which
> > explains the change in the resolution (I'd be happy to provide more
> > examples or information to anyone who is interested. It seems to me
> > that this may not be the the desired behaviour for WCS. I would expect
> > to get my data back at the same resolution requested. I haven;t seen
> > any bug reports on this (I did a search for WCS and only found 6
> > reports that matched wcs and none seemed to be about this issue). So
> > does someone know if I this is a bug or if I don't fully grasp WCS and
> > this is the desired response? Or is there a way to override this
> > behaviour or is there perhaps something wrong wiht my build?
>
> Ben,
>
> I'd appreciate it if you could file a bug on this.  You can assign it
> to me if you wish.  I've run into some "quirky" issues that may be
> related as I test my WCS client support in GDAL against mapserver.
> I think there may be some poor rounding choices and/or some
> "middle of pixel vs. top left corner of pixel" origin issues at play.
>
> > Question 2:
> >  We would like to return data to people at the actual resolution they
> > requested. To this end I am working on using wxs mapscript and php to
> > examine the request and return the correct resolution. I want to be
> > sure I don't stomp all over the WCS standard in the process though. So
> > the question is does anyone have any thoughts onteh following process.
> > If a user specifies no resx/resy or width/height I would calculate the
> > appropriate width and height for the bbox to return full res data. If
> > they specify resx/resy, but not width and height I'll caculate the
> > appropriate width and height to return the data at the requested resx
> > and resy for the bbox. If a user specifies a width and height I will
> > assume they know how the width and height and bbox relate and return
> > the data as requested. Does anyone feel like this goes againt the WCS
> > standard?
>
> Providing a full resolution default if no resx/resy or width/height
> are provided seems reasonable, though I personally prefer for the
> mapserver core wcs functionality to continue to treat this as an
> unspecified condition and issue an error.
>
> You write "If they specify resx/resy, but not width and height I'll
> calculate the appropriate width and height to return the data at the
> requested resx and resy for the bbox."  Doesn't this already happen?
> Are you just looking to fiddle with things a bit to work around the
> problem in point (1)?  If so, I think fixing the underlying problem
> would be the best approach.
>
> Best regards,
> --
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
>
>