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Geo-referencing in the UK - EPSG 27700 or WGS84


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I recall having a chat with the esteemed @Tamsin Slatter about geo-referencing and the fact that in order to correctly locate the geo-referencing for the UK we need to use EPSG 27700, which equates (although is not exactly equal to) CRS OSGB36, and there is a UK template set up using these settings.

 

However, doing a bit of reading up on the subject of coordinate systems and wondering why VW defaults to WGS84, I find that OSGB36 has been deprecated (since 2014) in favour of WGS84 in the UK since 2014, although the OS coordinate system are still related to OSGB36, apparently.  Not common knowledge I admit but made me wonder; Does it matter?

 

If we use EPSG 27700 or WGS84 in the geo-referencing settings, does it matter?

 

What is affected if we use one over the other?  It would seem more logical to leave the default as WGS84 if the results are the same.  When testing this and flipping between the two systems the coordinate shown in a stake object is correct in both systems, and we can easily locate the OS coordinate in both systems using online tools.

 

Where I am sitting right now has an OS coordinate of

 

X    528950m
Y    183675m

 

but this is either

 

Lat,Long (WGS84)    51.53725734571111,-0.14213076565247473
or
Lat,Long (OSGB36)   51.5367506099237,-0.1405246708102461

 

depending which system is defined.

 

Obviously there is quite a large discrepancy if we use the wrong coordinate system and enter the lat and long from the other coordinate system, but this of course would not happen, at least not on my watch!

 

All this is slightly academic given the proximity of the sun to the earth, and the value of setting the geo-referencing to the nearest mm, or as was the case on an ongoing project in Paris where they insisted on 0.1mm accuracy (because they can in Revit), has yet to be proven.

 

No-one sets out buildings using latitude and longitude, at least not in my experience, so what does this really affect, and should we care?  Should we simply use WGS84 now if that's the default in the UK since 2014?

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