source: trunk/README.GMAPS @ 821

Last change on this file since 821 was 736, checked in by Dominic Hargreaves, 16 years ago

More Google Maps tweaks.

File size: 2.2 KB
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1As of 0.52, OpenGuides supports Google Maps using the API. The support has a
2few rough edges that still need ironing out, mostly relating to ellipsoids,
3and for that reason they aren't exposed by default.
4
5To use Google Maps, you need to get an API key from
6http://www.google.com/apis/maps/signup.html. When you've put this value into
7the config file as gmaps_api_key, the maps become available to you in two
8places. Firstly, if the user has set the user preference to display Google
9Maps, any node which has location information will get an inset map
10pinpointing the location. Secondly, the URL
11http://.../wiki.cgi?action=index;format=map becomes a large map with a list
12of all nodes (regardless of the user settings). The latter will become very
13slow on any sizable guide (there is work being done on speeding up indexes
14in general - please see the mailing list). If you don't get maps displayed
15when you know that the node has location information, read on.
16
17Ellipsoids and map accuracy
18---------------------------
19
20If you are based in the US and inputting points using latitude/longitude,
21the values in your database will almost certainly correspond to points on
22Google Maps. If so, simply change the "ellipsoid" configuration variable
23to "WGS-84" if it's not already set to this, and your maps will display.
24
25If you are using the British Grid system things are more complicated and this
26support is incomplete. If you set the configuration variable force_wgs84
27to 1, maps will display, but points will be offset from where they should
28be, normally by about 50 metres. This is because the British Grid uses a
29different ellipsoid from Google Maps. We plan to integrate conversion
30routines to fix this in a future release. In the meantime, if you
31advertise the maps you must make users aware of this flaw and tell them
32not to try and "correct" location data!
33
34You may be unlucky enough to be using the UTM input modes (ie not British
35or Irish National Grid) but have data entered in a mixture of formats.
36This is likely if your users are from the UK, as you may find a mixture of
37WGS-84 and Airy (ie British Grid style) based nodes. In this case, you
38*do* need to correct any that are offset. Only do this if your users
39input Lat/long values rather than grid Eastings/Northings.
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