expoweb/handbook/survey/gps.htm

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<title>CUCC Expo Surveying Handbook: GPS</title>
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<h2 id="tophead">CUCC Expo Surveying Handbook</h2>
<h1>Locating entrances by GPS</h1>

<h3>Which point to fix</h3>

<p>The entrance to a cave significant enough to get a number and a survey
will eventually be marked by a numbered tag attached to a spit. This
will then become the primary survey station - ie. the point where an
underground survey will start, and the point to which a surface survey
should go. It's worth thinking about where you would put such a tag right
from the start. Unlike the first rigging bolt (often used as the first
point of a survey in the past) it should be sited with a particular
view to its visibility and accessibility without having to put on SRT
kit. If such a point has a clear view of the majority of the sky, then
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>
<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.

<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
the GPS on the point. Don't build a cairn, they don't last for decades and we have survey stations that old. 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
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>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
marker spit, looking for other caves, or even having lunch!) Remember to stop
the waypoint averaging before moving the unit or changing the display page.
<b>Take a photo of your GPS point showing at least one of your cave entrances
too.</b></p>

<p>We all use the same coordinate system WGS84 these days, so <a href="coord2.html">the extensive discussion 
on coordinate systems</a> has been moved to a different page. If you are really interested you can read 
<a href="coord.htm">Olaf's article</a>too.


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[svn r5797] All this bloody mess now validates as XHTML 1.0 Strict. What's more, some of the obviously out of date bits have been updated, or at least notes written to warn people that the information is out of date. I couldn't be arsed to do the surveying guide as well. I've just spent about eight hours doing this, I need food! 2004-04-22 19:13:46 +01:00			`<html>`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00			`<head>`
[svn r5797] All this bloody mess now validates as XHTML 1.0 Strict. What's more, some of the obviously out of date bits have been updated, or at least notes written to warn people that the information is out of date. I couldn't be arsed to do the surveying guide as well. I've just spent about eight hours doing this, I need food! 2004-04-22 19:13:46 +01:00			`<title>CUCC Expo Surveying Handbook: GPS</title>`
[svn r5766] Added CSS stylesheet tags to everything in sight. 2004-04-21 10:35:34 +01:00			`<link rel="stylesheet" type="text/css" href="../../css/main2.css" />`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00			`</head>`
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[svn r5828] More trivialities: redid centering the initial subheading 'CUCC Expedition [XXX] Handbook' using CSS rather than hard-coding into individual pages. 2004-04-24 12:50:58 +01:00			`<h2 id="tophead">CUCC Expo Surveying Handbook</h2>`
[svn r5797] All this bloody mess now validates as XHTML 1.0 Strict. What's more, some of the obviously out of date bits have been updated, or at least notes written to warn people that the information is out of date. I couldn't be arsed to do the surveying guide as well. I've just spent about eight hours doing this, I need food! 2004-04-22 19:13:46 +01:00			`<h1>Locating entrances by GPS</h1>`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00
[svn r6872] Changed area definitions to something slightly more helpful 2005-05-31 14:10:49 +01:00			`<h3>Which point to fix</h3>`

[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00			`<p>The entrance to a cave significant enough to get a number and a survey`
			`will eventually be marked by a numbered tag attached to a spit. This`
			`will then become the primary survey station - ie. the point where an`
			`underground survey will start, and the point to which a surface survey`
			`should go. It's worth thinking about where you would put such a tag right`
			`from the start. Unlike the first rigging bolt (often used as the first`
			`point of a survey in the past) it should be sited with a particular`
			`view to its visibility and accessibility without having to put on SRT`
			`kit. If such a point has a clear view of the majority of the sky, then`
[svn r5797] All this bloody mess now validates as XHTML 1.0 Strict. What's more, some of the obviously out of date bits have been updated, or at least notes written to warn people that the information is out of date. I couldn't be arsed to do the surveying guide as well. I've just spent about eight hours doing this, I need food! 2004-04-22 19:13:46 +01:00			`this is the point to use for a GPS fix too.</p>`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00
			`<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`
Tidying GPS links and updating 2018-08-11 10:42:43 +01:00			`landmark with a wide, clear view of the sky, and within one (or maybe two) survey shots`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00			`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`
[svn r5797] All this bloody mess now validates as XHTML 1.0 Strict. What's more, some of the obviously out of date bits have been updated, or at least notes written to warn people that the information is out of date. I couldn't be arsed to do the surveying guide as well. I've just spent about eight hours doing this, I need food! 2004-04-22 19:13:46 +01:00			`accurate) fixes on each entrance.</p>`
*fix and GPS 2023-10-16 23:48:28 +01:00			`<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.`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00
Tidying GPS links and updating 2018-08-11 10:42:43 +01:00			`<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`
2017-AMS-01 and ent fixes 2023-10-17 22:17:49 +01:00			`and GPS devices don't generally tell you how inaccurate the altitude is.`
Tidying GPS links and updating 2018-08-11 10:42:43 +01:00
[svn r6872] Changed area definitions to something slightly more helpful 2005-05-31 14:10:49 +01:00			`<h3>Taking the fix</h3>`

[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00			`<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`
2017-AMS-01 and ent fixes 2023-10-17 22:17:49 +01:00			`the GPS on the point. Don't build a cairn, they don't last for decades and we have survey stations that old. Give the GPS device a`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00			`couple of minutes to get a fairly good fix (the first figure reported may be`
[svn r6872] Changed area definitions to something slightly more helpful 2005-05-31 14:10:49 +01:00			`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 – 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.`
2017-AMS-01 and ent fixes 2023-10-17 22:17:49 +01:00			`Averaging the readings like this is vital if you want an even vaguely accurate altitude reading.</p>`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00
			`<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`
[svn r6872] Changed area definitions to something slightly more helpful 2005-05-31 14:10:49 +01:00			`marker spit, looking for other caves, or even having lunch!) Remember to stop`
			`the waypoint averaging before moving the unit or changing the display page.`
			`<b>Take a photo of your GPS point showing at least one of your cave entrances`
			`too.</b></p>`

Tidying GPS links and updating 2018-08-11 10:42:43 +01:00			`<p>We all use the same coordinate system WGS84 these days, so <a href="coord2.html">the extensive discussion`
			`on coordinate systems</a> has been moved to a different page. If you are really interested you can read`
			`<a href="coord.htm">Olaf's article</a>too.`
Fix typo in y rotation on GPS page Also link to more accurate version of the transformation on coords.htm. 2017-07-22 01:14:48 +01:00
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00
*fix and GPS 2023-10-16 23:48:28 +01:00			`<hr /></body>`
[svn r3779] Added HTML files. 2001-08-15 19:29:27 +01:00			`</html>`