[mapserver-dev] Support for the MapInfo style zoom layering option.

[Steve Lime]

So how is a current ZOOM value computed? How would this impact symbol and font scaling?

Steve

>>> On 6/16/2008 at 7:53 AM, in message
<f3b73b7d0806160553j3d7ebb4u50c7d9ec60ed83ce at mail.gmail.com>, "Tamas Szekeres"
<szekerest at gmail.com> wrote:
> Hi All,
> 
> I have been asked to incorporate in mapserver a support for the
> MapInfo style zoom layering functionality.
> By using this approach the displayable range of the layer could be
> specified in map units in addition to the current
> MINSCALEDENOM/MAXSCALEDENOM parameters.
> 
> An example of the related changes in the mapfile could be considered as:
> 
> LAYER
>        NAME 'test'
>        ...
>        DISPLAYRANGE ZOOM
>        MINZOOM 1000
>        MAXZOOM 5000
> 
>        MINSCALEDENOM 10000  # Would be ignored because layer's zoom type is 
> ZOOM
>        MAXSCALEDENOM 20000  # ''
> END
> 
> 
> Depending on the DISPLAYRANGE setting (the possible values could be
> ZOOM and SCALE) the visibility of the layer could be determined based
> on
> the extent of the layer (in map units) or by using the current scale
> based approach.
> 
> The main difference between these options is how the display range
> depends on the screen size. Zoom layering (MapInfo style) appears to
> be screen size independent,
> however the zoom scaling depends on the width of the screen in pixels
> (which affects the scale).
> 
> 
> The proposed solution (above) will require to add 3 new elements (an
> integer and 2 doubles) to the related objects (not only the layerObj-s
> will be affected)
> by adding a slight increment in the memory usage of the application.
> Though it would be comfortable by the user having both of the values
> stored, but we could eventually save 2 doubles by
> storing the minzoom/maxzoom values in minscaledenom/maxscaledenom (in
> exchange for a slight confusion about the names)
> 
> 
> Before getting forward to write an RFC for this addition I would like
> to see whether this kind of implementation or any variant would be
> acceptable by the PSC or not, so let me know your thoughts.
> 
> 
> Best regards,
> 
> Tamas
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