<div dir="ltr"><div dir="ltr">Hi Jim,<div><br></div><div>Here is a full article on how projections (specifically the British National Grid) work in QGIS and what you can do to improve your data collection when using on-the-fly transformation:</div><div><a href="https://merginmaps.com/docs/gis/projections/#projections">https://merginmaps.com/docs/gis/projections/#projections</a></div><div><br></div><div>Kind regards</div><div>Saber</div><div><br></div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Fri, 1 May 2026 at 19:36, Jim Jackson via QGIS-User <<a href="mailto:qgis-user@lists.osgeo.org">qgis-user@lists.osgeo.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
<br>
QGIS version  3.40.6-Bratislava<br>
QGIS code branch Release 3.40<br>
OS Linux Devuan GNU/Linux 6 (excalibur) (basically Debian Trixie)<br>
<br>
Hi All,<br>
<br>
As a member of a community Archaeology Group, I'm using QGIS for recording <br>
archaeological features in the UK. I'm using Google Satellite, <br>
OpenStreetMap and National Library of Scotland historic basemaps, which (as <br>
I understand it) use EPSG:3857.<br>
<br>
I have an RTK GPS receiver for collecting data points which are in <br>
EPSG:4326. <br>
I <br>
also get UK National Grid data points from a colleague who has access to a <br>
total station.<br>
<br>
As I think I understand it, I need to set the project CRS to UK national <br>
grid EPSG:27700 to get sensible distance measurements However I then get <br>
occasional warnings "Used a ballpark transform from EPSG:27700 to <br>
EPSG:3857" indicated less than accurate transformations, and then I get <br>
lost!!!!<br>
<br>
Can anyone point me to a tutorial on how to set up QGIS in the UK to get <br>
accurate transformations in these circumstances (which can't be that <br>
unusual).<br>
<br>
Any advice and/or pointers where I've gone wrong gratefully received.<br>
<br>
Jim Jackson<br>
<br>
<br>
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</blockquote></div><div><br clear="all"></div><div><br></div><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><span><table style="color:rgb(34,34,34);border-width:medium;border-style:none;border-color:currentcolor;border-collapse:collapse"><colgroup><col width="131"><col width="206"></colgroup><tbody><tr style="height:96pt"><td style="border-bottom:1.5pt solid rgb(58,46,38);vertical-align:top;padding:5pt;overflow:hidden"><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial,sans-serif;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline"><span style="border-width:medium;border-style:none;border-color:currentcolor;display:inline-block;overflow:hidden;width:110px;height:110px"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfRShNz3_eaBwmELBh6Hs7NISwJ0zBAxXuQRdfMTx_KVwquAkDNsfSKlWCAD8EybEacpoT8D-Ad_6aPTn6ZinwLy8yenLedZcL_kN2QhKMps99TX9RprZSUz62v-PKGspTi1sYOMg?key=Jeb2bYt9w71cI5NxZsG4pEQm" width="110" height="110" style="margin-left: 0px; margin-top: 0px;"></span></span></p></td><td style="border-bottom:1.5pt solid rgb(58,46,38);vertical-align:top;padding:5pt;overflow:hidden"><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span style="font-size:13pt;font-family:Arial,sans-serif;color:rgb(0,0,0);background-color:transparent;font-weight:700;vertical-align:baseline">Saber Razmjooei</span></p><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(102,102,102);background-color:transparent;vertical-align:baseline">Co-Founder</span></p><br><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><a href="http://lutraconsulting.co.uk/" style="color:rgb(17,85,204)" target="_blank"><span style="font-size:11pt;font-family:Arial,sans-serif;background-color:transparent;vertical-align:baseline">lutraconsulting.co.uk</span></a></p><br><p dir="ltr" style="line-height:1.2;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial,sans-serif;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline"> </span><a href="https://www.linkedin.com/in/saber-razmjooei/" style="color:rgb(17,85,204)" target="_blank"><span style="font-size:11pt;font-family:Arial,sans-serif;background-color:transparent;vertical-align:baseline"><span style="border-width:medium;border-style:none;border-color:currentcolor;display:inline-block;overflow:hidden;width:20px;height:20px"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXd-3nSSZboZbZSIGiTp73Ozx31KSI7AbhDKGZ81W0DJ_P1BZpenwIUStbXjOV163hSfCvthvBVB800Mv3A0DLnKiXVjCFCRS2DI1xIy7nluSZwyqofUNSSjgyZAx5WowWiporGU?key=Jeb2bYt9w71cI5NxZsG4pEQm" width="20" height="20" style="margin-left: 0px; margin-top: 0px;" alt="https://www.linkedin.com/in/saber-razmjooei/"></span></span></a><span style="font-size:11pt;font-family:Arial,sans-serif;color:rgb(0,0,0);background-color:transparent;vertical-align:baseline"> </span><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfYoSmPP0wTWr2uNEJLnWTQriFM7yw6Yx67z0lzAbv2MElfGvAIGSM-95hu65e4tYm-XGVL0I3oLdcyw4uUCim9-H1S0ajfdoNV0VWj1bwLOI8KAk2-_sBWN_hSpe5w6qukE1J8sg?key=Jeb2bYt9w71cI5NxZsG4pEQm" width="20" height="20" style="margin-left: 0px; margin-top: 0px;"> <a href="https://www.youtube.com/@LutraConsulting" style="color:rgb(17,85,204)" target="_blank"><span style="font-size:11pt;font-family:Arial,sans-serif;background-color:transparent;vertical-align:baseline"><span style="border-width:medium;border-style:none;border-color:currentcolor;display:inline-block;overflow:hidden;width:20px;height:20px"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXcw8vIlzwnam9KCAL7KEQvBL2hmQrtO0p9Vs75AIP1ouSLFr8SIuHQTg3VD5UPONIxhpHmH1B2lX8s1Bryl3qiEd4_U2yiiYQxhhmy63yT8h0Eua4N3vVv0eMFnw26Jh7elQhnm?key=Jeb2bYt9w71cI5NxZsG4pEQm" width="20" height="20" style="margin-left: 0px; margin-top: 0px;"></span></span></a><span style="background-color:transparent;font-size:11pt;font-family:Arial,sans-serif;color:rgb(0,0,0);vertical-align:baseline"> </span><a href="https://github.com/lutraconsulting" style="color:rgb(17,85,204)" target="_blank"><span style="font-size:11pt;font-family:Arial,sans-serif;background-color:transparent;vertical-align:baseline"><span style="border-width:medium;border-style:none;border-color:currentcolor;display:inline-block;overflow:hidden;width:20px;height:20px"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfg4gx274581StgEzMK155DxfmkmhrSRDSL7rPkPRmxhAMzSE8qlWwODdpAnoXaUPeztgveka9xMzeoZgRG6WhOOXYlXHdTt3G3xcEV6qmJyoAvd_68a-PuYRlJtjz3W9qf0MPGFA?key=Jeb2bYt9w71cI5NxZsG4pEQm" width="20" height="20" style="margin-left: 0px; margin-top: 0px;"></span></span></a></p><br></td></tr><tr style="height:97.5pt"><td colspan="2" style="border-top:1.5pt solid rgb(58,46,38);vertical-align:top;padding:5pt;overflow:hidde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