Mark,
Sounds ok (it took me a while to realize you meant the BBOX of the
polygons, not the label!).
My world of sophisticated labeling would include some way of having
the mapfile specify the order of applying the rules, but currently there
is no way to do procedural things in a mapfile, just set parameters. On
second thought, I guess the CLASS list evaluates things in a particular
order; perhaps the same technique could be used in label placement:
LABEL
CHECKLABELFIT true # Check BBOX of label against polygon outline
(not just BBOX of polygon)
LOCATION# --- first label attempt (Case A,B) ---
POSITION cc,ul,uc,ur
END
LOCATION# --- next label attempt (Case C) ---
ANGLE auto
END
LOCATION# --- next label attempt (Case D) ---
LEADER
:
END
END
END
And I'd like to factor in preferring labeling in areas of no other
linework, but that may take some thought...
Best Regards,
Brent Fraser
On 12/12/2012 10:40 AM, Mark Volz wrote:
Brent,
In the long run when servers get faster, more layers get cached, and users
expect better cartography, I think that it would be worthwhile to implement a
way of trying multiple positions. The CHECKLABELFIT keyword is mostly to
verify that a label falls inside the actual polygon as opposed to the BBOX,
which would help avoid ambiguity on labels. I don't think CHECKLABELFIT would
be mutually exclusive to any method of trying to find different label positions.
In your comments you have the term "If it doesn't fit." CHECKLABELFIT could be
used to specify if we consider if the label fits according to the BBOX or the polygon.
For example:
A: Calculate the default location of the label in the polygon. If
CHECKLABELFIT is on: only place the label if it falls inside the polygon. If
CHECKLABELFIT is off: only place the label if it fits in the BBOX
If the label could not be placed, and TRYALTERNATELABELS is on:
B: Try different positions in the polygon UL,UC,UR, etc. If
CHECKLABELFIT is on: only place the label if it falls inside the polygon. If
CHECKLABELFIT is off: only place the label if it fits in the BBOX
If a label still could not be placed:
C: Rotate the label. If CHECKLABELFIT is on: only place the label if it
falls inside the polygon. If CHECKLABELFIT is off: only place the label if it
fits in the BBOX.
If a label could not be placed after rotating the label
D. Try using a leader line. / Place Polygon annotation outside polygon.
Use situations:
CHECKLABELFIT=FALSE, TRYALTERNATELABELS=FALSE: label the map as fast as
possible.
CHECKLABELFIT=TRUE, TRYALTERNATELABELS=FALSE: make sure labels fit in their
polygons, but don't worry about labeling everything.
CHECKLABELFIT=FALSE, TRYALTERNATELABELS=TRUE: try to label as many items as
possible, use the BBOX as label ambiguity is okay.
CHECKLABELFIT=TRUE, TRYALTERNATELABELS=TRUE: try to label as many items as
possible, and make sure that the labels fit inside their polygons. (slowest)
Thanks
Mark Volz
GIS Specialist
-----Original Message-----
From: Brent Fraser [mailto:[email protected]]
Sent: Wednesday, December 12, 2012 10:01 AM
To: Mark Volz
Cc: [email protected]
Subject: Re: [mapserver-users] Still impossible to force labels inside their
polygons?
Mark,
A simple solution sounds good as long as it can fit into a strategic plan (I
don't really have a plan for improving the polygon labeling, just a desire!).
On major releases of Mapserver I try to push the limits of its cartography
by comparing its output to hand-composed pdfs of Canadian Topo maps [1]
(not fair I know). One of the stumbling blocks I've run into is the labeling of
polygons and I've speculated on the use of "rules-based" labeling. Here's my
list of rules from a comment on RFC
77 [2].
"Allow for alternate label positions. While this is likely beyond the
scope of
RFC 77, perhaps it could be taken into account in design and implementation
for later addition. Basically I'd like more flexibility (rule-based?) in
labeling
polygons:
A. Try to place label in polygon. If it doesn't fit:
B. Rotate label to fit inside a polygon. If it doesn't fit:
C. Place polygon annotation outside polygon"
I wonder if adding keywords like CHECKLABELFIT (and other new ones) is the
way to go or use PROCESSING directives instead?
[1]
http://geogratis.cgdi.gc.ca/geogratis/en/product/search.do?id=A6291EF5-
F3FC-A29F-3162-DE4DB194FD38
[2] http://lists.osgeo.org/pipermail/mapserver-dev/2011-
December/011773.html
Best Regards,
Brent Fraser
On 12/11/2012 7:33 AM, Mark Volz wrote:
Hello,
Earlier in the year I had asked about forcing labels in their polygons. And
another person mentioned the issue in September. At the time Steve W was
concerned about complexity and performance in placing labels. I was
thinking lately that maybe this topic could be revisited. However, this time
around instead of dealing with "optimal" label placement within a polygon,
maybe something much simpler would be better. For example:
keyword : CHECKLABELFIT
-FALSE: Use the BBOX for labeling. This is the current behavior, which is
fast and should remain as the default.
-TRUE: Once the label is placed using the current label placement engine,
check to make sure the BBOX of label falls within the actual boundary of the
polygon, if it does not then skip the label.
This keyword should not be confused with any algorithm that places labels
in an optimal position within the polygon such as one that tries to place a
label horizontally, then strait if it doesn't fit. Last, since check label fit
is
optional, this keyword should only impact performance on layers that a user
wants to verify that the label is correctly placed. It would never be needed
for a layer where the polygons are rectangular such as sections, or
townships. However it may be critical on soil layers.
Just some thoughts
Thanks
Reference
http://osgeo-org.1560.n6.nabble.com/force-labels-to-fit-in-polygons-td
4549296.html
http://comments.gmane.org/gmane.comp.gis.mapserver.user/49333
Mark Volz
GIS Specialist
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