[mapserver-dev] Better resolution handling for printing

[Tamas Szekeres]

Alan,

I think this issue is more about a theoretical than a technical problem. It
depends on how do we define the concept of the resolution related to the
size and sizeunit settings.
For example when we set sizeunit=MS_PIXELS and setting the symbolsize to 8,
I consider the every would expect to draw the symbol at exactly 8 pixels in
width regardless of the actual resolution setting.

On the other hand we could declare alternative concepts as well. For example
we declare that this is only the case when the resolution is set exactly to
72.0 dpi and at any other setting the actual drawing width will
increase/decrease proportionately. If this concept is acceptable then you
could safely multiply the scalefactor with resolution/72.0 when drawing the
symbols/labels in the code.

However you might want to allow the user to set this magnification factor
manually either by using this new parameter or the using
resolution/default_resolution concept mentioned by Daniel before.

Best regards,

Tamas



2009/2/18 Alan Boudreault <aboudreault at mapgears.com>

> Tamas,
>
> I would like to add the resolution handling for printing transparently
> without
> the necessity to use another keyword. And if we decide to add the
> "magnification" keyword ulteriorly, we will probably be able to use the
> same
> code/functions.
>
> Any other thoughts about how could we achieve the better resolution
> handling?
> Else, i'll begin to check in code for the best way to increase/decrease all
> values dependently of the resolution value.
>
> Alan
>
> On February 11, 2009 05:19:10 pm Tamas Szekeres wrote:
> > Daniel,
> >
> > I would introduce a new parameter of the map called 'magnification' which
> > would be multiplied with the resolution when calculation the scale. In
> > addition the scalefactor should also multiplied with this in
> msPrepareImage
> > to achieve the desired effect.
> > I guess it wouldn't be annoying for the user that by setting
>  magnification
> > = 2.0 would increase the width of the map elements 2 times.
> > magnification = 1.0 would be the default value.
> >
> >
> > Best regards,
> >
> > Tamas
> >
> >
> >
> >
> >
> > 2009/2/11 Daniel Morissette <dmorissette at mapgears.com>
> >
> > > Dev's,
> > >
> > > When using MapServer to generate a printable map at higher resolution
> > > than the default screen resolution, say 300dpi instead of 72dpi, it is
> > > not sufficient to update the map->resolution setting since all the
> label
> > > and symbol sizes as well as line widths also need updating if you want
> to
> > > maintain the same map appearance.
> > >
> > > This issue has been discussed a few times before and I even think some
> > > have worked on this at their end. We have a client who needs a fix for
> > > this so I'd like to open a discussion on this before we go ahead and
> > > prepare a RFC.
> > >
> > > The approach I was thinking of using is to add a new map->defresolution
> > > (better names welcome) that would be the default resolution of a given
> > > mapfile, that is the reference resolution for which all sizes in
> labels,
> > > classes and styles are set.
> > >
> > > In normal web browsing operation, map->defresolution should be set to
> the
> > > same value as map->resolution (e.g. 72dpi). When you want to print a
> > > 300dpi map, then you'd set map->resolution=300, and MapServer would
> > > automagically apply a factor of map->resolution/map->defresolution to
> all
> > > size values in the mapfile before rendering. For instance, if your
> > > mapfile is set for a defresolution of 72dpi and you request a output
> > > resolution of 300dpi, all size values would be multiplied by
> 300/72=4.16
> > > and labels, lines and symbols on the resulting map would have the
> > > same/expected relative sizes.
> > >
> > > I think I've read suggestions of setting resolution as an outputformat
> > > option before, but this may not work well with remote (e.g. WMS)
> > > services, we need something better integrated and with the proposed
> > > approach just passing a new vendor-specific resolution param in the WMS
> > > GetMap URL could do the trick.
> > >
> > > Does my explanation make sense? Has anyone worked on this problem
> > > already? Any thoughts on this before we start working on a RFC?
> > >
> > > Daniel
> > > --
> > > Daniel Morissette
> > > http://www.mapgears.com/
> > > _______________________________________________
> > > mapserver-dev mailing list
> > > mapserver-dev at lists.osgeo.org
> > > http://lists.osgeo.org/mailman/listinfo/mapserver-dev
>
>
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