[ka-Map-users] max_extents and EXTENT

[ramesh karra]

Thank you Tim!

This really helps! I really appreciate your prompt 
and very informative responses.

I made the changes accordingly and the map displays
and does not allow me to drag at the highest
scale/zoom level in Firefox, exactly as I wanted.

But when I use Internet Explorer, the behavior is
slightly different. In Internet Explorer, the map is
moved very slightly, at the highest scale/zoom level.
Basically, the picture 'shakes' when I try to drag at
the highest scale.

Do you know of any browser dependencies that I should
take care of?

Thanks
Ramesh


--- Tim Schaub <tim at commenspace.org> wrote:

> > Is there a better way to determine these values
> other than 
> > trial and error? i.e., for a given extent, is
> there a formula 
> > to determine exact maximum scale value for a given
> display 
> > image size (of Width x Height)?
> 
> This is not ka-Map specific, but you can figure out
> map units given
> scale, resolution, and screen units.
> 
> Given a scale, to get the width of your extent in
> map units:
> 
> Extent Width = Display Width x Scale Denominator /
> (Resolution x Inches
> per Map Unit)
> 
> where "Display Width" is the width of your map
> viewport in pixels,
> "Scale Denominator" is the mapserver scale,
> "Resolution" is the
> resolution according to mapserver (default is 72
> dpi), and "Inches per
> Map Unit" depends on your map units (inches: 1,
> feet: 12, miles: 63360,
> meters: 39.3701, kilometers: 39370.1, decimal
> degrees: 4374754).
> 
> So, for example, if you have a 400 pixel viewport
> and you want to know
> the width of your extent in meters for a scale of
> 1:250000, use
> 
> EW = 400 pixels x 250000 / (72 dpi x 39.3701 inches
> per meter) = 35228 m
>  
> If you know of a point that you want centered,
> subtract & add half of
> that width to get the minx & maxx portion of your
> extent.  Do similar
> for the height, miny & maxy.  If you have an extent
> width (or height)
> and want scale, you should be able to flip that
> around.
> 
> Hope that helps,
> Tim
> 
> 
> > 
> > Thanks
> > Ramesh
> > 
> > --- Tim Schaub <tim at commenspace.org> wrote:
> > 
> > > Hey Ramesh-
> > >  
> > > > Sorry for not mentioning that my EXTENT and
> > > max_extents are
> > > > exactly same! In that case I do not expect any
> > > difference in
> > > > the behavior!
> > > 
> > > I should have mentioned that both EXTENT and
> max_extents 
> > can both be 
> > > overridden by scale.
> > > 
> > > It could be that I am misunderstanding your
> problem, but 
> > I'm guessing 
> > > that your largest scale (in mapserver terms)
> forces ka-Map 
> > to render 
> > > an area larger than your EXTENT (and
> max_extents).  If this is the 
> > > case, your EXTENT will be centered in the map
> viewport - but the 
> > > viewport will show an area beyond your EXTENT
> (and you 
> > should not be 
> > > able to pan around due to max_extents).  When
> you zoom in 
> > to your next 
> > > scale, you can no longer pan to the area outside
> of your EXTENT 
> > > because of your max_extents.
> > > 
> > > So, the bottom line is that you'll always be
> able to 
> > specify a scale 
> > > that violates your EXTENT and max_extents.  Note
> that this is a 
> > > dangerous practice (to specify a scale that
> requires tiles to be 
> > > rendered outside of your EXTENT) if you are
> relying on pre-caching 
> > > tiles.  The pre-caching script doesn't know how
> big your 
> > viewport is 
> > > going to be, so it assumes that you don't need
> more than a 
> > 1 metatile 
> > > buffer around your EXTENT or max_extents - if
> specified.
> > > 
> > > Tim
> > > 
> > > > 
> > > > Ramesh
> > > > 
> > > > --- Tim Schaub <tim at commenspace.org> wrote:
> > > > 
> > > > > Hey Ramesh-
> > > > > 
> > > > > > I have a question regarding max_extents
> > > METADATA.
> > > > > I have both
> > > > > > EXTENT and METADATA max_extents defined in
> my
> > > map
> > > > > file. At
> > > > > > the highest zoom level(maximum scale), the
> map
> > > > > shows a point
> > > > > > X which is very close to the left border
> of
> > > > > 'max_extents' I
> > > > > > have defined. But when I zoom-in one level
> I
> > > > > cannot see this. 
> > > > > > Basically, I cannot drag that far left.
> Any
> > > ideas
> > > > > on why this
> > > > > > could be happening?
> > > > > 
> > > > > The max_extents METADATA option does not
> > > override your
> > > > scale settings.
> > > > > So, if you have a max_extent defined that is
> > > smaller than
> > > > the extent
> > > > > of the map at your highest zoom level (at
> some
> > > browser
> > > > window size),
> > > > > ka-Map will still display the area outside
> the
> > > max_extents.
> > > > >  So, the zoom level
> > > > > (scale) has precedence when there is a
> conflict.
> > > > > 
> > > > > When you zoom in a bit, you are restricted
> in
> > > panning by
> > > > max_extents.
> > > > > 
> > > > > Let me know if you think something else is
> going
> > > on.
> > > > > 
> > > > > Tim
> > > > > 
> > > > > > 
> > > > > > Thanks
> > > > > > Ramesh
> > > > > > 
> > > > > >
> > >
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> >
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