[Qgis-user] Best practice when using UK national grid and GPS

[Jim Jackson]

QGIS version  3.40.6-Bratislava
QGIS code branch Release 3.40
OS Linux Devuan GNU/Linux 6 (excalibur) (basically Debian Trixie)

Hi All,

As a member of a community Archaeology Group, I'm using QGIS for recording 
archaeological features in the UK. I'm using Google Satellite, 
OpenStreetMap and National Library of Scotland historic basemaps, which (as 
I understand it) use EPSG:3857.

I have an RTK GPS receiver for collecting data points which are in 
EPSG:4326. 
I 
also get UK National Grid data points from a colleague who has access to a 
total station.

As I think I understand it, I need to set the project CRS to UK national 
grid EPSG:27700 to get sensible distance measurements However I then get 
occasional warnings "Used a ballpark transform from EPSG:27700 to 
EPSG:3857" indicated less than accurate transformations, and then I get 
lost!!!!

Can anyone point me to a tutorial on how to set up QGIS in the UK to get 
accurate transformations in these circumstances (which can't be that 
unusual).

Any advice and/or pointers where I've gone wrong gratefully received.

Jim Jackson