[OpenLayers-Users] Query Feature by Attribute and Zoom

[Richard Greenwood]

On Thu, Apr 10, 2008 at 12:39 PM, groby <groby at tce.coop> wrote:
>
>  Hello,
>
>  I am fairly new to OpenLayers and GIS in general and new to this list.  I
>  have just setup an OpenLayers page.  I am using MapServer as my WMS Server
>  and my data is held in PostGIS tables.
>
>  I would like to know how can I create a way for a user to input text and to
>  zoom to the feature specified by the text.
>
>  An example of what I am trying to accomplish:
>  Take the Feature Info Example at
>  http://www.openlayers.org/dev/examples/getfeatureinfo.html.  If I wanted to
>  make it so a user could type in a country name then have the map zoom to the
>  extent of the country, how would I do so?  It needs to be a general enough
>  example I could use it with any text field (for example, a Serial Number).
>
>  I have found a few previous postings that seem to be asking a similar
>  question but not many answers.  Any pointers to a nice or ugly solution are
>  appreciated.
>
>  Thanks.
>
>  Greg


There are a couple ways to get an extent.

1. Making a non-WMS call to mapserver like:

   http://localhost/cgi-bin/mapserv?map=/path/to/mapfile.map&mode=itemnquery
     &qitem=id&qstring=123456&qlayer=ownership&mapext=shapes

Using a simple mapfile like:
    [minx], [miny] [maxx], [maxy]

Would return the extent of the feature(s) where id=123456. You could
then use those values to set the OL extent. You can also use itemquery
and itemnquery modes to highlight feature(s).

2. If your data in in PostGIS you can call the extent() function e.g.:

    SELECT extent(the_geom) FROM sometable WHERE id=123456;

I have a small php page that I call with the query parameters and it
returns the extent, which I then use to set the extent in the browser.
In the mapfile I have a layer styled with a bright highlight. The
layer has a filter so I again pass the id=123456 to select the objects
that I want to highlight e.g.: FILTER "%id%"

These suggestions may not be the WMS way, or the OL way, but they are
tried-and-true MapServer methods for highlighting features and getting
extents.

HTH

-- 
Richard Greenwood
richard.greenwood at gmail.com
www.greenwoodmap.com