[mapserver-users] Display TAB point layer but get label from a second tab file

[Daniel Morissette]

On 11-06-06 06:29 PM, Peter Girgis wrote:
> Hi all
>
> I wonder if anyone can assist me with this issue.
> I have a TAB file which contains points and a second TAB file which
> contains the labels.
> The two TAB files are relational so I can look up the label using a
> unique id however I cannot work out whether it is in fact possible to
> display labels from a second TAB file based on a query.
>
> This is similar to JOIN where you would lookup labels from a csv or
> database however I canot see an option to do this from a TAB file.
>

You could use a OGR SQL statement in the DATA parameter of your layer to 
join the two tables. This won't be very efficient since I don't think 
OGR will take advantage of any index in this case, but could be worth a 
try if your files are not too large.

e.g. something like the following (untested)

LAYER
    NAME "mylayer"
    TYPE POINT
    CONNECTIONTYPE OGR
    CONNECTION "/path/to/points.tab"
    DATA "SELECT * from points LEFT JOIN '/path/to/labels.tab'.labels on 
points.id = labels.id"
    STATUS ON
    CLASS
      ...
    END
...
END

For more info on OGR SQL, see:

http://www.gdal.org/ogr/ogr_sql.html

... and use the ogrinfo utility to experiment and test your SQL statement.

Another option may be to setup a VRT to join the two tables... that 
would be doing essentially the same thing internally, except that the 
SQL statement would be inside the VRT file:

http://www.gdal.org/ogr/drv_vrt.html
http://mapserver.org/input/vector/VirtualSpatialData.html


-- 
Daniel Morissette
http://www.mapgears.com/
Provider of Professional MapServer Support since 2000