root/tags/rel0_62/README.GMAPS

As of 0.52, OpenGuides supports Google Maps using the API. The support has a
few rough edges that still need ironing out, mostly relating to ellipsoids,
and for that reason they aren't exposed by default.

To use Google Maps, you need to get an API key from
http://www.google.com/apis/maps/signup.html. When you've put this value into
the config file as gmaps_api_key, the maps become available to you in two
places. Firstly, if you've set "show_gmap_in_node_display", and if the user
has set their preferences to display Google Maps, any node which has
location information will get an inset map pinpointing the location.
Secondly, the URL
http://.../wiki.cgi?action=index;format=map becomes a large map with a list
of all nodes (regardless of the user settings). The latter will become very
slow on any sizable guide (there is work being done on speeding up indexes
in general - please see the mailing list). If you don't get maps displayed
when you know that the node has location information, read on.

Ellipsoids and map accuracy
---------------------------

If you are based in the US and inputting points using latitude/longitude,
the values in your database will almost certainly correspond to points on
Google Maps. If so, simply change the "ellipsoid" configuration variable
to "WGS-84" if it's not already set to this, and your maps will display.

If you are using the British Grid system things are more complicated.
To display accurate maps, you need to have the optional perl module
Geo::HelmertTransform installed (libgeo-helmerttransform-perl in Debian).
If this isn't possible, you can still get Google Maps to display by setting
the configuration variable force_wgs84 to 1, but points will be offset from
where they should be, normally by about 50 metres. This is because the
British Grid uses a different ellipsoid from Google Maps. This is not
recommended; if you do so, you must make users aware of the flaw and tell
them not to try and "correct" location data!

You may be unlucky enough to be using the UTM input modes (ie not British
or Irish National Grid) but have data entered in a mixture of formats.
This is likely if your users are from the UK, as you may find a mixture of
WGS-84 and Airy (ie British Grid style) based nodes. In this case, you
*do* need to correct any that are offset. Only do this if your users
input Lat/long values rather than grid Eastings/Northings.