[Talk-GB] Georeferencing / zeroing imagery

[Colin Smale]

On 2019-09-14 17:14, SK53 wrote:

> Hi Edward, 
> 
> In general the GPS rule is still the best way of doing it, we used to have access to Strava heatmap which was very good, but no longer. 
> 
> Other viable alternatives are:  
> 
> * OS OpenData road centrelines. Of course if you use a crude OSGB->WGS84 based on OSGB36 this may be upto 5 m out anyway (maximum error of the straight conversion). 
> * Open Data sets which have probably been very accurately located (Nottingham Streetlights, trees in Bristol, Birmingham etc). I presume councils use some kind of differential GPS to locate assets.
> * OS StreetView layer was rectified by Grant using OSGB-02 and is good to crosscheck across layers for shifts.
> * Lidar data from Enivornment Agency/SEPA etc doesn't suffer from parallax errors and can be useful for identifying shifts also.

Admin boundaries imported from OS Boundary-Line should also be accurate,
provided they haven't been moved or otherwise "improved" during / after
the initial import. If the ways are source=OS_OpenData_Boundary-Line and
the nodes are still at version 1, I would think they should be reliable.
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