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Incorrect waypoint locations in GM GPX extract from SOTLAS in 2021

Last year I did an extract of summits from sotlas and downloaded them as a GPX file to my GPS. I have only owned a GPS for around a year and still only use it to confirm summit locations on ambiguous summits.

I recall during my activation of GM/WS-011 the gpx location was debatable as to whether it was even within the AZ.

Fast forward to last week and I experienced a larger error on GM/SI-014.

I have done some digging and my gpx file extracted from sotlas (from last year dated 2021-06-18T13:23:20.026Z) has the following for GM/SI-014.

Extract from SOTLAS today:

> <wpt lat="56.96563" lon="-6.31468">
>     <ele>781</ele>
>     <name><![CDATA[GM/SI-014 - Ainshval]]></name>
>     <cmt><![CDATA[Ainshval]]></cmt>
>     <sym>SOTA04</sym>
>     <type>Summit</type>
>   </wpt>

GPX file in my GPS (extract from SOTLAS June 2021):

  <wpt lat="56.9664" lon="-6.3139">
    <ele>781</ele>
    <name><![CDATA[GM/SI-014]]></name>
    <cmt><![CDATA[Ainshval]]></cmt>
    <sym>SOTA04</sym>
    <type>Summit</type>
  </wpt>

Not sure if this was database updates, SOTLAS rounding/precision that has been subsequently fixed? Either way, a timely reminder:

  • Don’t rely on a GPS, map and compass skills are crucial (as in the case for SI-014 I was in 20m vis and this incorrect waypoint was located in steep complex mountain crag terrain);
  • It is probably worth updating your GPX files on your GPS for GM.

73 Matthew M5EVT.

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I’m fairly sure there were some GM position tweaks in the last GM update, that was the one which deleted maybe 8 summits and add 4 or so new summits.

Maybe it’s because I know how the update process works, but if I need summit positions for the GPS I download as near to the activation as possible to ensure I always have the latest data.

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The current lat/lon values are provided from the Relative Hills of Britain download. Previous values would have been sourced from a coordinate conversion of the 6-figure grid reference. The conversion itself was possibly not so precise and anyway the gridref (from RHoB) was updated. So yes, it’s good to watch out for our (monthly) announcements and take special note when we say there were position tweaks to your association:

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Thank you both for the reply. It seems most likely this is related to GM association updates and nothing to do with SOTLAS.

I did see this update at the time as I have ambitions for GM/NS-154. However, I didn’t give enough thought to what the word minor might mean:

most summits positions and heights getting minor adjustments

I decided to quantify this. I quickly threw together a python script to compare the two gpx files and calculate (geodesic) distances between to old and new waypoints.

I don’t have easy access to the data to quantify how many of these were outside of the activation zone.

I filtered any change > 150 m:

GM/CS-043 - Geal-charn, 162.3 m
GM/CS-069 - An Dun, 369.5m
GM/CS-083 - Meall na Leitreach, 156.0 m
GM/NS-142 - Cnoc an Daimh Mor, 197.1 m
GM/NS-144 - Creag a’Ghobhair, 498.2 m
GM/SI-068 - Sgurr na Stri, 181.0 m
GM/SI-090 - Beinn Bhreac, 367.0 m
GM/SI-108 - Guainemol, 187.7 m
GM/SI-123 - Beinn Chreagach, 301.7 m
GM/SI-205 - Sotan, 545.7 m
GM/SS-086 - Beinn Ruadh, 159.4 m
GM/SS-090 - Beinn Dubh, 155.6 m
GM/SS-106 - Cauldcleuch Head, 183.7 m
GM/SS-131 - Hods Hill, 210.2 m
GM/SS-178 - Craignell, 162.0 m
GM/SS-230 - The Slate, 155.0 m
GM/WS-051 - The Saddle, 211.7 m
GM/WS-053 - Maoile Lunndaidh, 639.6 m
GM/WS-106 - The Fara, 151.8 m
GM/WS-233 - Carn Breac, 165.2 m
GM/WS-260 - Beinn na Feusaige, 299.2 m

Lesson learnt, if I see any association update, update the GPX file.

73 Matthew M5EVT.

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None. Checking such things is part of the process. Where the new / old AZs do not overlap we raise a new ref and retire the old one. As you have noticed sometimes a new ref is not necessary even for a significant move.

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Apologies, I perhaps wasn’t clear in my reply. What I meant was, “how many of these old waypoints were outside of the activation zone of the “true” summit”.

For example:

My June 2021 GPX extract waypoint location for SI-014 on a cliff approx 80 m elevation less than the summit?

My June 2021 GPX extract waypoint location for SI-205 in the sea?

73 Matthew M5EVT.

This is my extract of Sotan from a set of UK summit coordinates that predate the last update to GM.

sotan
©Crown copyright 2022 Ordnance Survey. Media 041/22

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Likewise Askival


©Crown copyright 2022 Ordnance Survey. Media 041/22

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The corresponding entries for the above waypoints in the GPX file I extracted from SOTLAS (2021-06-18T13:23:20.026Z)

<wpt lat="56.7826" lon="-7.6466">
    <ele>193</ele>
    <name><![CDATA[GM/SI-205]]></name>
    <cmt><![CDATA[Sotan]]></cmt>
    <sym>SOTA01</sym>
    <type>Summit</type>
  </wpt>

 <wpt lat="56.9664" lon="-6.3139">
     <ele>781</ele>
     <name><![CDATA[GM/SI-014]]></name>
     <cmt><![CDATA[Ainshval]]></cmt>
     <sym>SOTA04</sym>
     <type>Summit</type>
   </wpt>

73 Matthew M5EVT.

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I’ve done some digging and my “old” waypoints file used the NGR to set the summit marker not lat&long which is why it doesn’t look to be in too bad a position on that map.

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None of the old summit locations were outside of the AZ as updated, for summits which did not receive a new ref. As to exact GPX way-marker locations, as outlined they may have been subject to reduced accuracy owing to the conversion process from NGR (with inherent 100-m resolution - as you can see from your histogram most sit nicely in the 0-to-100-m range). Nevertheless the actual summit locations would have been easily identifiable (e.g. keep at the top of the cliff / don’t go for a swim). RHoB provide lat/lon nowadays, as per GNSS results†, so there is no conversion process and you should be pretty safe to target the coordinates blindly. Of course I am speaking figuratively! Caution near cliffs is recommended.

Old and new locations of GM/SI-205 with the activation zone:


©Crown copyright 2022 Ordnance Survey. Media 041/22

As you can see the old summit location (as per our working files - can’t comment on GPX) were/are both in the AZ (this is taken from OS Terrain5 DTM). It’s actually a fairly close call, with RHoB recording a 20-m drop to the col. I’m not sure why we didn’t update the name to “Sron an Duin” though.

[† Where RHoB have made a GNSS survey, which is still not everywhere I think. But whatever they have we have kept full resolution in GM.]

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