[Talk-GB] Georeferencing / zeroing imagery

[Edward Bainton]

Hi folks

Another query from me that I imagine has been done to death elsewhere (so
apologies), but I haven't found it on the wiki. The usual disclaimer that
I'm not well up on the technical side of the map.

I've read the wiki on Using Imagery
<https://wiki.openstreetmap.org/wiki/Using_Imagery> and have understood
that the best way of 'zeroing' the offset of imagery is to look for GPS
traces, albeit even they are somewhat inaccurate.

A few questions:
- Over how wide an area does an offset obtained that way hold good?
- Are the old OS maps better/worse/same as this system? Are they an
alternative for zeroing imagery?
- If I know the grid reference of somewhere (eg, Environment Agency puts a
10-fig reference on a plaque on their assets) is that any help?

On the last point, this wiki page
<https://wiki.openstreetmap.org/wiki/Key:ele> mentions OSGM02. The link has
rotted so I searched their site which gives hits for OSGM15
- Is 02 an outdated standard that I should update on the wiki?

Thanks,

Edward / eteb3
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