How can I dynamically supply the value of mapextents to the Mapfile?

Question

Is it possible to query a PostGIS database from a browser where I set the extents of the map?

I have previously queried a PostGIS database from the browser and, separately, used MapServer to display a raster using a WMS query. Now I'm wondering if I can join these two separate pieces together. The part that I am not understanding is how to insert the query into the MapServer code. For example, if my MapServer layer piece is as follows:

LAYER  # start layer 
            CONNECTIONTYPE postgis
            NAME "roads
            CONNECTION "user=username 
            password=**** dbname=databasename host=hostdb.com port=5434" 
            DATA "geom from tablename where ST_Intersects(geom, mapextents)"
            STATUS ON
            TYPE LINE
            CLASS
                STYLE
                    COLOR 0 0 0
                END
             END
END # end layer

How can I dynamically supply the value of mapextents to the MapServer file? I have considered the .map piece usually to be static but perhaps this is incorrect.

An example of the type of query that I want to perform is as follows:

SELECT
    ST_Clip(r.rast, 'POLYGON((-8293673 4952790,-8137619 4952790,-8137619 5036076, -8293673 5036076,-8293673 4952790))'::geometry)   
FROM    
    raster AS r                 
WHERE       
    ST_Intersects(r.rast, 'POLYGON((-8293673 4952790,-8137619 4952790,-8137619 5036076, -8293673 5036076,-8293673 4952790))'::geometry)

Secondly, where should I be storing the .map file? At the moment I have them in a web readable folder but I know this is not a good strategy once I need to store a password.

Answer 1

Mapserver has a flexible interface for dynamically manipulating the map configuration via special parameters in the url. The documentation is available at:

http://mapserver.org/cgi/controls.html#cgi-mapfile-change-parameters

In your case:

 ...&map.extent=123 123 456 567&...

At the end of the same section there is also an example of how to use the same run-time substitution to hide the map file path. Usually you would place the map file in a path is not directly served by apache (ie outside the web root).

Please remember to set the correct permissions on the map file and associated data so that the apache user can access it (read permission is enough).