[Mapserver-users] Limiting min and max scale when usingMapScript

[Lowell Filak]

I also use the trial & error method on the scales.
There is one other option for limiting the zooms:
If your using 4.0 you should be able to use the new methods for
mapObjzoom that Sean Gillies added.
The new methods appear to have zoom limits built in.
Lowell

The following message was sent by Eric Bridger <eric at gomoos.org> on 31
Jul 2003 10:47:45 +0000.

> I always set min and max scales by trial and error.  In a template you
> can display [scale] to see the current scale.  In mapscript I use a perl
> function taken from the C code.
> 
> When using mapscript you can use MINXSCALE and MAXSCALE for LAYER's,
> etc. but since you don't have a WEB object (the script must create the
> WEB html by itself) setting $map->{web}->{maxscale} will have no affect.
> 
> Here's the perl code I use to prevent zooming out beyond the original
> map extent:
> #########################
> # @imgext is the current map extent from the map form
> # default is original extent
> my $mapext = join(' ',
>
$map->{extent}->{minx},$map->{extent}->{miny},$map->{extent}->{maxx},$map->{extent}->{maxy});
> if($zoom_direction < 0){
>   my $max_scale = calculateScale($map, $map->{extent}->{minx},
> $map->{extent}->{maxx});
>   my $current_scale = calculateScale($map, $imgext[0], $imgext[2]);
>   if($current_scale  >= $max_scale){
>      return $mapext;
>   }
> }
> #########################################
> # from mapserver3.6.4: mapscale.c msCalculateScale().  This is not a
> precision thing. We don't worry about
> # msAdjustExtent() since in all our maps, image SIZE has same aspect
> ratio as the map EXTENT.
> sub calculateScale{
>     my ($map, $minx, $maxx) = @_;
>     if(!$minx){
>         $minx = $map->{extent}->{minx};
>         $maxx = $map->{extent}->{maxx};
>     }
>     my @inchesPerUnit = (1, 12, 63360.0, 39.3701, 39370.1, 4374754);
>     my $width = $map->{width};
>     my $units = $map->{units}; # index into unitsPerUnit array
>     my $resolution = $map->{resolution};
>     my $md = $width / ($resolution * $inchesPerUnit[$units]);
>     my $gd = $maxx - $minx;
>     return($gd/$md);
> }
> 
> 
> Eric
> 
> On Thu, 2003-07-31 at 09:22, AMC Story wrote:
> > Hi there everyone,
> > 
> > Firstly, I was hoping someone could tell me how to arrive at
sensible figures 
> > for minscale and maxscale as specified in the web object?  The exact
derivation 
> > of these values has been questioned several times in the archives
but I haven't 
> > yet managed to find an answer, maybe this could be added on to the
mapfile 
> > reference doc?
> > 
> > Also, I think I remember seeing somewhere that if you are using
MapScript as 
> > opposed to the CGI application, you can't specify a minscale and
maxscale value 
> > in the mapfile.  I've tried just setting these values in my script:
> > 
> > $current_map->{web}->{maxscale}=some number?;
> > $current_map->{web}->{minscale}=some number?;
> > 
> > but whatever values I use this doesn't seem to make any difference.
> > 
> > Can someone let me know how I can stop users from zooming in and out
too far?
> > 
> > Thanks very much,
> > Ali
> > _______________________________________________
> > Mapserver-users mailing list
> > Mapserver-users at lists.gis.umn.edu
> > http://lists.gis.umn.edu/mailman/listinfo/mapserver-users
> > 
> 
> 
> _______________________________________________
> Mapserver-users mailing list
> Mapserver-users at lists.gis.umn.edu
> http://lists.gis.umn.edu/mailman/listinfo/mapserver-users