AW: [UMN_MAPSERVER-USERS] turn layer labels on and off dynamically

[Stephen Woodbridge]

Arnd Wippermann wrote:
> Hello Steve,
> 
> Someting I have always searched, but to lazy to look into the documentation.
> This parameters one can also set with cgi. 
> 
> Thanks for the info

I have not tried this, but I think the syntax would be something like:

map_<layer_name>_labelrequires=0   to turn off the the labels.

replace <layer_name> with the name of the layer. Probably best if you do 
not have spaces in the layer name.

-Steve W.

> Mit freundlichen Grüssen
> 
> Arnd Wippermann
> http://gis.ibbeck.de/ginfo/
> 
> 
> 
> -----Ursprüngliche Nachricht-----
> Von: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] Im
> Auftrag von Stephen Woodbridge
> Gesendet: Mittwoch, 30. Mai 2007 05:26
> An: MAPSERVER-USERS at LISTS.UMN.EDU
> Betreff: Re: [UMN_MAPSERVER-USERS] turn layer labels on and off dynamically
> 
> Gregor Mosheh wrote:
>>> I am using the Java MapScript for my application and I would like to 
>>> present the option for the user to decide whether or not to show 
>>> labels for a given layer. Is there any way to turn the label for a 
>>> layer on or off dynamically? I didn't see anything obvious in the
> MapScript API.
>> Speaking from the world of PHP/Mapscript, with hopes that it's 
>> applicable to your situation... Our solution is to set the label color 
>> to something invalid, to suppress the rendering of labels, e.g.:
>>
>>    $class = $layer->getClassNyName('roads');
>>    if (!$labels) {
>>       $class->label->color->setRGB(-1,-1,-1);
>>    }
>>
>>
>>
> 
> Ooops, that does not quite work the way you are expecting it to. color
> -1 -1 -1 means transparent. so you are rendering the labels but they are
> just transparent. Since you are rendering the labels, it takes cpu time and
> it might bump other labels out of the cache. I don't think you really want
> to do this.
> 
> A better solution might be to set the LABELMINSCALE or LABELMAXSCALE to a
> value that would force the labels off, then reset the value to its normal
> value to turn them back on based on the zoom scale.
> 
> You might also be able to use LABELREQUIRES "0" | "1" to turn on/off labels.
> 
> Both of these are LAYER attributes.
> 
> I have not played with either of these, but you should be able to get one of
> them to work.
> 
> -Steve W.
> 
>