Dear Jackey Cheung,

I am not sure what exactly you are trying to achieve.
Your arrows seem to point in the direction of the lines.
The topmost arrow in figure 1 is placed at a strange
position - is that the problem?

Some comments:

The result shown in image 2 is expected.  The arrow
symbols are in this case placed at the start points of
the lines according to the centre point of the symbol's
bounding rectangle (except 0,0 is always taken as the
upper left corner of the bounding rectangle).
When using a negative GAP, the direction of the symbol
is the direction of the line at the (end)point.
In version 6.2, ANCHORPOINT is introduced to make it
possible to specify a different anchor point for the
symbol (http://mapserver.org/trunk/mapfile/symbol.html).

The centre point of the bounding box of your arrow_right
symbol will be at (17.5,7) in the symbol's coordinate
system, so the arrows will be placed somewhat shifted to
the right (in the direction of the arrow).
In 6.0, if you want the ends of the arrows to be aligned
with the start of the lines (when using geomtransform
start), you could use the following symbol:

SYMBOL
  NAME "arrow_right_shift"
  TYPE VECTOR
  POINTS
    30 6
    52 6
    50 0
    60 7 # why 7.5?
    50 14
    52 8
    30 8
    30 6
  END
  FILLED TRUE
END

In 6.2, you will be able to specify this using
ANCHORPOINT 1 0.5


HÃ¥vard

On 11/10/2011 06:35 AM, Jackey Cheung wrote:
Hi all,

We are trying to render line direction on 6.0.1. However, there are
something weird with it.


SYMBOL
   NAME                 "arrow_right"
   TYPE VECTOR
   POINTS
     5 6
     27 6
     25 0
     35 7.5
     25 14
     27 8
     5 8
     5 6
   END
   FILLED  TRUE
END


LAYER
   NAME              "traffic_direction"
   STATUS            DEFAULT
   TYPE              LINE
   MAXSCALEDENOM     5000

   CONNECTIONTYPE    POSTGIS
   PROCESSING        "CLOSE_CONNECTION=DEFER"
   CONNECTION        "host=xxxxxxx dbname=******* user=xxxxxxxxxx
password=************"
   DATA              "geom FROM view_render_traffic_direction USING
UNIQUE oid USING SRID=4326"

   CLASS
     NAME            "Traffic Direction"
     STYLE
       ANGLE         AUTO
       SYMBOL        "arrow_right"
       SIZE          6
       COLOR         0 0 250
       GAP           -200
       #GEOMTRANSFORM "start"
     END
   END
END


The layer above is rendered as 1.PNG. We've checked that there are
only one line (ring) there, but arrows are rendered problematic.
Then we've tried to change GEOMTRANSFORM to "start" or "end", then
rings seem OK, but all arrows at intersections got crossed, as 2.PNG.
We've also tried to use OFFSET and GAP with positive and negative
combinations, but none can solve the problem.

Can anyone shed some light for us? Thanks in advance.
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