[mapserver-users] force labels to fit in polygons

[Stephen Woodbridge]

Right, the problem has two parts:

1) determine potential candidate label points
2) see if the label fits given the constraints placed on how to draw it

This is NP hard problem because it not just a problem of labeling a 
single polygon you also have to deal with all the other labels on the 
map that you might collide with.

If you search "automatic label placement" in google you can read up on 
the problem and the solutions that are available. Mapserver uses a 
different scheme for doing label placement that is much faster because 
it does not try to optimize label placement, but rather gives you 
controls for how labels should be placed, like POSITION, ANGLE 
AUTO|FOLLOW, PROCESSING "LABEL_NO_CLIP=ON", PRIORITY, WRAP, 
MINFEATURESIZE, MAXLENGTH, PARTIALS, etc.

By the way, PROCESSING "LABEL_NO_CLIP=ON" will fix the label point at 
the polygon center.

-SteveW

On 3/6/2012 6:13 AM, Patricio Gigoux wrote:
> You could generate a center point, there is a function that do it in
> irregular shaped, and fit the label in it
>
> Patricio Gigoux
>
>
>
>
> El 05-03-2012 18:50, Stephen Woodbridge escribió:
>> On 3/5/2012 4:44 PM, Mark Volz wrote:
>>> Hello,
>>> Is there a way to force labels to fit inside of a polygon, even if a
>>> polygon is irregularly shaped? I noticed that with POSITION AUTO labels
>>> are falling outside of my soils boundary.
>>
>> The short answer is no. It is an interesting problem, but it does not
>> have a guaranteed result as the label might be too big to fit
>> regardless. I am not even sure of the algorithm should be for
>> something like this. There are a lot of parameters like:
>>
>> font
>> font size
>> wrapping the text
>> changing the angle
>> finding the longest line, arc or smooth polyline that fits withing the
>> polygon and then have the text follow that line
>>
>> These are all computationally expensive to do on the fly while
>> rendering. Ideally these should be worked out in advance then you can
>> supply the attributes to the label via binding columns in the data.
>>
>> -SteveW
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