ScaleHint in GetCapabilities resquest

[Jacolin Yves]

Thanks Bart :)

Y.
Le Monday 22 October 2007 13:21:07 Bart van den Eijnden, vous avez écrit :
> Hi Yves,
>
> Mapserver's default resolution is 72 dpi, that should explain your
> difference.
>
> However I would encourage you to change this in the MAP file if you are
> running an OGC service, you should use:
>
> MAP
>   ..
>   RESOLUTION 90.714
>   ..
>
> instead according to the OGC.
>
> Best regards,
> Bart
>
> On 10/22/07, Jacolin Yves <yjacolin at free.fr> wrote:
> > Le Friday 19 October 2007 16:24:03 Daniel Morissette, vous avez écrit:
> > > Jacolin Yves wrote:
> > > > Hi list,
> > > >
> > > > After a GetCapabilities resquest on a mapserver server, I find this
> >
> > line
> >
> > > > inside my xml file:
> > > > <ScaleHint min="9.97805696859274" max="249.451424214819" />
> > > >
> > > > In my mapfile, I defined min et max scale values with:
> > > >    MINSCALE 20000
> > > >    MAXSCALE 500000
> > > >
> > > > How can I convert the scaleHint value to the mapfile value? In other
> > > > words, what does scaleHint values means?
> > >
> > > WMS defines the scalehint values as the ground distance in meters of
> > > the southwest to northeast diagonal of the central pixel of a map.
> > > ScaleHint values are the min and max recommended values of that
> > > diagonal. (See WMS 1.1.0 sect. 7.1.5.4)
> > >
> > > It is calculated in msWMSPrintScaleHint() in MapServer's mapwms.c:
> > >
> > >    diag = sqrt(2.0);
> > >
> > >    if (minscaledenom > 0)
> > >      scalehintmin =
> > > diag*(minscaledenom/resolution)/msInchesPerUnit(MS_METERS,0);
> > >    if (maxscaledenom > 0)
> > >      scalehintmax =
> > > diag*(maxscaledenom/resolution)/msInchesPerUnit(MS_METERS,0);
> > >
> > >
> > > The use of inchesPerUnit conversion is because resolution is in pixels
> > > per inch, and we need the result in meters.
> > >
> > > I'll leave it as an exercise to you to figure out the reverse
> > > conversion (scalehint -> scaledenom). ;)
> > >
> > > Daniel
> >
> > Daniel,
> >
> > Does the default resolution of a map is 75 dpi?
> >
> > The reversion conversion should be : minScale =
> > (ScaleHint/diag)*resolution
> > with diag = sqrt(2.0);
> > resolution in pixel/m -> 2.54 E-02 pixel/inch (equal to dpi?)
> >
> > so minScale = (9.97805696859274/sqrt(2.0))*75/2.54*100
> > minScale = 20 833 (instead of 20 000)
> > maxScale = 520 833 (500 000)
> >
> > Does this differences are normal?
> >
> > Thanks,
> >
> > Y.
> > --
> > Yves Jacolin
> > ---
> > http://softlibre.gloobe.org



-- 
Yves Jacolin
---
http://softlibre.gloobe.org