[mapserver-dev] Better resolution handling for printing

[Alan Boudreault]

Hi Tamas,

I think the "magnification" concept could be good. I suppose that the 
resolution parameter will simply set internaly the magnification setting. What 
could be the behavior if the user use the magnification and the resolution? Is 
it a problem if we lost some precision with all integer values ? ie: if the 
magnification is set to "2.34", all interger values will be multiplied... but 
probably rounded after.

Thanks for you thoughts!
Alan 

On February 18, 2009 02:26:04 pm Tamas Szekeres wrote:
> 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/
> > > > _______________________________________________
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> >
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