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2004-04-22 19:13:46 +01:00
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<title>CUCC Expo Surveying Handbook: GPS</title>
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2004-04-21 10:35:34 +01:00
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2004-04-24 12:50:58 +01:00
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<h2 id="tophead">CUCC Expo Surveying Handbook</h2>
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<h1>Locating entrances by GPS</h1>
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<p>The entrance to a cave significant enough to get a number and a survey
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will eventually be marked by a numbered tag attached to a spit. This
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will then become the primary survey station - ie. the point where an
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underground survey will start, and the point to which a surface survey
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should go. It's worth thinking about where you would put such a tag right
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from the start. Unlike the first rigging bolt (often used as the first
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point of a survey in the past) it should be sited with a particular
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view to its visibility and accessibility without having to put on SRT
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kit. If such a point has a clear view of the majority of the sky, then
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this is the point to use for a GPS fix too.</p>
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<p>If however, you are dealing with a cave at the foot of a cliff, or
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otherwise with a restricted view of the sky, then choose instead a good
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landmark with a clear view, and within one (or maybe two) survey shots
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of the entrance. If you have found a group of caves close together, it
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might be better to GPS a central point rather than get quick (but less
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accurate) fixes on each entrance.</p>
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<p>Once you have chosen your point, mark it in some way (could be a spit hole
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or a cairn, for example - we aren't supposed to use paint any more) and place
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the GPS on the point. If you build a cairn, make it wide rather than high -
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tall cairns are knocked down by the depth of snow each winter. Give it a
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couple of minutes to get a fairly good fix (the first figure reported may be
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quite a way out, but after a couple of minutes things should settle). Then
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mark the point as a waypoint. If your GPS supports averaging, then choose
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"average" and leave the GPS to do its own averaging for half an hour or more.
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If it doesn't support averaging, then fix another waypoint at the same
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location just before you leave. This shows someone examining the track log
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later that all the track points relate to the same spot, and they can then do
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the averaging themselves.</p>
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<p>While the GPS is recording your location, you can do something useful
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(like rigging the cave, doing a surface survey from the GPS point to the
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marker spit, looking for other caves, or even having lunch!) It does not
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matter (and may be slightly beneficial) if you leave the GPS longer than half
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an hour. But if you want to use it for anything else, remember to stop the
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waypoint averaging before moving the unit or changing the display page. Take
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a photo of your GPS point showing at least one of your cave entrances too.</p>
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<p>It doesn't especially matter what display options are selected when you
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are getting the GPS fix, but it is important to use standard ones when
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writing down the reported position in the survey book. Currently we use
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"German" grid, "Austrian" datum, and "metric" units. All is not lost if you
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can't select this particular set, but it is very important that you <u>write
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down what was actually used</u>, since different grid systems can give
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results up to a couple of kilometres different!</p>
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<p>Write down the figure that the GPS gives for each waypoint at the time
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(just in case some failure loses the data from the GPS memory). That's all
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you need to do at the cave. Get the GPS data downloaded to a computer next
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time you are in Base Camp (or Top Camp if someone has a laptop :-). This
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should be put in a file and a clear reference to it put in the notKH survey
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book. Don't alter the file in any way - it may be necessary to upload it to
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a GPS unit at some time to do coordinate conversion. Also copy your written
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down data to the survey book with all the other details of your cave.</p>
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<p>If you want to read about the nitty gritty of converting GPS coordinates
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to the ones used by the Kataster system, you can do no better than read
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Wookey's <a href="../../years/1996/gps.htm">Compass Points Article</a>.
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Briefly, this says "it's horribly complicated and we don't really know how to
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do it properly". However, the main point of having a GPS fix on an entrance
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is so we can find it again and be sure it is the same one!</p>
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2004-04-22 19:13:46 +01:00
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<hr />
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<ul id="links">
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<li><b>Expedition Handbook:</b>
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<ul>
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<li>Expo Handbook <a href="../index.htm">Introduction</a></li>
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<li><b>Surveying:</b>
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<ul>
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<li>Surveying <a href="index.htm">Overview</a> and index of
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topics</li>
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<li><a href="what.htm">What is a cave survey?</a></li>
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<li><a href="why.htm">Why am I doing this?</a></li>
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<li>Methods: <a href="how.htm">underground</a></li>
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<li>Pitfalls to avoid, <a href="hints.htm">hints'n'tips</a> to
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make life easier</li>
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<li>Methods: <a href="ontop.htm">surface</a></li>
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<li>Base Camp: <a href="getin.htm">getting it in</a> to the
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computer</li>
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<li>Base Camp: <a href="drawup.htm">drawing it up</a>, writing
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the description</li>
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</ul></li>
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<li><a href="../look4.htm">Prospecting guide</a></li>
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<li><a href="../rescue.htm">Rescue guide</a></li>
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<li><a href="../rigit.htm">Rigging guide</a></li>
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<li><a href="../photo.htm">Photography guide</a></li>
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</ul></li>
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<li><a href="../../infodx.htm">Index to info/topics pages</a></li>
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<li><a href="../../indxal.htm">Full Index to area 1623</a>
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<ul>
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<li><a href="../../areas.htm">Area/subarea descriptions</a></li>
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</ul></li>
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<li><a href="../../index.htm">Back to Expedition Intro page</a></li>
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<li><a href="../../../index.htm">Back to CUCC Home page</a></li>
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</ul>
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2001-08-15 19:29:27 +01:00
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