[Mapserver-users] Re: polygon label placement

[blaise]

Dean Gadoury wrote :
-----
Every now and then I need to label polygons in MapServer and I'm often
unsatisfied with the resulting placement. Labeling is fine for points
and lines, but when it comes to polygons it can be unpredictable....
If I'm not mistaken the POSITION parameter will only place the label
relative to the point at which MapServer decides the label will go.
Depending on the label's POSITION its quite possible to have labels that
fall completely outside a polygon. Is there a way to force labels to be
within a polygon? Is there anything else I'm missing?
-----

I have seen some discussions some times ago in the list about having the 
polygon labels inside the polygons.
First try the different label position parameters (vertical : up, 
center, down; horizontal : left, center, right). (i.e. : CC)
If you can do some mapserver scripting, you can put the labels wherever 
you want (acoording you know where they have to go) :
-- have a separate label (or point) layer where you will draw the labels 
for the polygons,
-- for each polygon, compute the X/Y coordinates of each vertex to find 
the best point place for the label to be,
-- insert a label (or a labeled point) at this computed location on your 
label layer.

For the computation, you can use the simple :
X = middle of Xmin - Xmax
Y = middle of Ymin - Ymax
But this won't give you good results if you deal with "inside-curved" 
polygons.
I think you can find a lot of doc for the computation of the "center" of 
polygons.
You can have a look at a demo where you can precisly set the polygon 
labels with the simple computation above and by the means of two 
X-offset and Y-offset parameters :
http://webmaps.ouvaton.org    link: java-tools demo
(switch to html with the green java switch left to the scale bar (all 
editing and updating tools have not yet been developped in java), put 
the purple polygon layer in update mode and digitize new polygons or 
update the X/Y-offset of the existing ones, or update the vertex.)

'hope it'll help
Blaise