Changeset 960


Ignore:
Timestamp:
Mar 21, 2007, 2:56:14 PM (15 years ago)
Author:
Dominic Hargreaves
Message:

Fix documentation re British grid stuff.

File:
1 edited

Legend:

Unmodified
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  • trunk/README.GMAPS

    r953 r960  
    2424to "WGS-84" if it's not already set to this, and your maps will display.
    2525
    26 If you are using the British Grid system things are more complicated and this
    27 support is incomplete. If you set the configuration variable force_wgs84
    28 to 1, maps will display, but points will be offset from where they should
    29 be, normally by about 50 metres. This is because the British Grid uses a
    30 different ellipsoid from Google Maps. We plan to integrate conversion
    31 routines to fix this in a future release. In the meantime, if you
    32 advertise the maps you must make users aware of this flaw and tell them
    33 not to try and "correct" location data!
     26If you are using the British Grid system things are more complicated.
     27To display accurate maps, you need to have the optional perl module
     28Geo::HelmertTransform installed (libgeo-helmerttransform-perl in Debian).
     29If this isn't possible, you can still get Google Maps to display by setting
     30the configuration variable force_wgs84 to 1, but points will be offset from
     31where they should be, normally by about 50 metres. This is because the
     32British Grid uses a different ellipsoid from Google Maps. This is not
     33recommended; if you do so, you must make users aware of the flaw and tell
     34them not to try and "correct" location data!
    3435
    3536You may be unlucky enough to be using the UTM input modes (ie not British
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