[mapserver-dev] Labeling enhancements not related to justification

[Steve Lime]

I'd say callouts are out of scope for Thomas' proposal. Thomas and I exchanged
notes awhile back on possibly using special styleObj TYPES as a way to do stuff
like this. We were talking about arrow heads but the thought was that other custom
renderers could be supported. One could be a bbox renderer that draws the mbr
around a polygon or polyline. I'm wondering if a callout renderer could also be
supported. I like the idea of AUXPOINT but would just go with POINT in the label
object as a way to override the computed point (that could be done now, with binding). 
The arrow, marker or other styling would come from the STYLE object with TYPE CALLOUT 
or something like that. Post 5.2 work I fear...

Steve

>>> Stephen Woodbridge <woodbri at swoodbridge.com> 05/06/08 1:53 PM >>>
Thomas,

The one request I get a lot from users is for an arrow label based on an 
axillary label placement point. This would be like how google labels the 
small states on the US Eastern seaboard with the label in the ocean and 
an arrow pointing to where the object label point is.

I would propose a syntax like this into implement this, but something 
else might be better if anyone has any ideas.

    LABEL
      ....
      AUXPOINT [label_x] [label_y]
      ....
    END

Where the [label_x], [label_y] are column references and this point 
would be used to place the label text and then an arrow would be 
constructed back to the objects label point from this AUXPOINT. If 
[label_x],[label_y] is equal to 0,0 then default labeling behavior would 
apply and the AUXPOINT would be ignored.

One could also set up FILTERs to select label_x != 0 to separate 
AUXPOINT labels from standard labels if they wanted to.


You could also add an optional arrowhead style and size fields, like: 
[ah_style] and [ah_size]:

      AUXPOINT [label_x] [label_y] [ah_style] [ah_size]

which could be used to determine what style of arrow to use. Like:

[ah_style]:
    plain - simple line
    arrow - line with arrowhead
    dot   - line with dot instead of arrowhead

[ah_size] controls the size of the arrowhead or dot


[label_x] [label_y] [ah_style] [ah_size] can be constants or column 
substitutions.

LabelCache processing would look at the bbox for the label text, not the 
arrow, or if looking at the arrow also would only look at the arrow path 
not the arrow's bbox. Maybe some more thought needs to go into this part 
of the proposal.

-Steve W.
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