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Added links to other GPS pages and editing very old GPS advice - online edit of handbook/survey/gps.htm

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Philip Sargent
2025-05-11 15:46:20 +01:00
committed by Expo on server
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commit 8d2ac0c0c6
1 changed files with 22 additions and 14 deletions
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handbook/survey/gps.htm
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@@ -7,6 +7,9 @@
<h2 id="tophead">CUCC Expo Surveying Handbook</h2>
<h1>Locating entrances by GPS</h1>
<h3>First actions</h3>
<p>First of all, you need to <a href="/handbook/computing/myphone.html">set up your phone</a> in "expo mode" for recording locations on the plateau reliably. This is not just some technical settings, it also means a particular style of useage whch you need to learn.
<h3>Which point to fix</h3>
<p>The entrance to a cave significant enough to get a number and a survey
@@ -22,29 +25,31 @@ this is the point to use for a GPS fix too.</p>
<p>If however, you are dealing with a cave at the foot of a cliff, or
otherwise with a restricted view of the sky, then choose instead a good
landmark with a wide, clear view of the sky, and within one (or maybe two) survey shots
of the entrance. If you have found a group of caves close together, it
might be better to GPS a central point rather than get quick (but less
accurate) fixes on each entrance.</p>
landmark with a wide, clear view of the sky, and with at least two survey shots
of the entrance. </p>
<p>Yes, you will have to manually do a surface survey leg using your survey instruments between the GPS point and the cave entrance tag station, and record that in your cave survex file.
<p>We now (2018) have differential GPS which is much more accurate than
in the past (e.g. Wookey's 1996 article) but altitudes are often very inaccurate
and GPS devices don't generally tell you how inaccurate the altitude is.
<p>Since 2018 we have differential GPS which renders historical advice obsolete (e.g. Wookey's 1996 article) but altitudes are still always inaccurate
and GPS devices don't generally tell you how inaccurate they are. Also phones are now much more complicated than the dedicated GPS devices used in the past. It is now
<a href="/handbook/computing/myphone.html">the phone itself</a> we have to worry about, not just GPS. Phones try to be "helpful" these days and do not tell you what they are doing.
<h3>Taking the fix</h3>
<p>Once you have chosen your point, mark it in some way (could be a spit hole
or a cairn, for example - we aren't supposed to use paint any more) and place
or a cairn, for example - we don't use paint any more) and place
the GPS on the point. Don't build a cairn, they don't last for decades and we have survey stations that provide permanent locations. Give the GPS device a
couple of minutes to get a fairly good fix (the first figure reported may be
quite a way out, but after a couple of minutes things should settle). Then mark
the point as a waypoint. If you're feeling really keen, you can set it up for
<i>averaging</i>, which gives a more accurate fix &ndash; some GPS receivers
minute to get a fairly good fix (the first figure reported may be
quite a way out is you have been moving). Then mark
the point as a waypoint (dedicated GPS devices or GPS apps only).
<h4>Averaging</h4>
<p> If you're feeling really keen and have a dedicated GPS device or sophisticated GPS app,
you can set it up for <i>averaging</i>, which gives a more accurate fix &ndash; some GPS receivers
support this automatically, and with others you can just leave it recording a
track log, then record another waypoint at the same place just before you leave
so it's clear to someone examining the track log when you actually left.
Averaging the readings like this is vital if you want an even vaguely accurate altitude reading.</p>
</p>
<p>While the GPS is recording your location, you can do something useful
(like rigging the cave, doing a surface survey from the GPS point to the
@@ -58,5 +63,8 @@ on coordinate systems</a> has been moved to a different page. If you are really
<a href="coord.htm">Olaf's article</a>too.
<hr />
<a href="newcave.html">Next survey guide page - 'Base Camp: getting it in to the computer'</a></body>
<a href="newcave.html">Next survey guide page</a> - 'Base Camp: getting it in to the computer'<br />
<a href="/handbook/computing/myphone.html">Your phone on expo</a> - Do not select the "high accuracy" location setting on your phone<br />
<a href="/handbook/essentials.html">GPS essentials on the plateau</a> - Safety information<br />
<a href="/logbookentry/2024-07-21/2024-07-21c">Photo GPS</a> - Is unreliable unless you follow procedure<br /></body>
</html>