From 5bda2880144b9f1193d83305418de10f397b9318 Mon Sep 17 00:00:00 2001 From: Philip Sargent Date: Thu, 22 May 2025 09:15:12 +0100 Subject: [PATCH] updated gps - online edit of handbook/survey/ontop.htm - on dev machine 'SnowWhite' --- handbook/survey/ontop.htm | 23 ++++++----------------- 1 file changed, 6 insertions(+), 17 deletions(-) diff --git a/handbook/survey/ontop.htm b/handbook/survey/ontop.htm index 0e71914dd..4528d5ef1 100644 --- a/handbook/survey/ontop.htm +++ b/handbook/survey/ontop.htm @@ -4,7 +4,6 @@ -

CUCC Expo Surveying Handbook

Surface surveys

@@ -57,11 +56,11 @@ the whole survey!

Entrances and holes

All features of speleological interest should have their position recorded exactly. -These days (2018) a long-average (200+ readings) GPS location is fine (see GPS for entrances) in most parts of our caving area. -This usually means using a handheld GPS device rather than a phone unless you have a particularly -good GPS app which provides an averaging function. + These days (2025) a medium-average GPS location (3 minutes: i.e. 1,000+ GPS "events" inside your device) is fine (see GPS for entrances) in most parts of our caving area. + (This is not "accurate": it will be perhaps 5m off if you measure the same spot the next day when the ionosphere is in a different mood, and any altitude you get will be absolutely useless.) +This usually means using a handheld GPS device rather than a phone unless you have a specifically accurate GPS app (e.g. OSMand) which provides both an averaging function and does not assume that you are a cyclist or fell-runner (most Garmin devices in 2025). -

If you are close to a big cliff, or almost inside an overhang, then an averaged-GPS will be good (~ 2m accuracy) +

If you are close to a big cliff, or almost inside an overhang, then an averaged-GPS will apparently be good (~ 2m accuracy) for latitude/longitude but appallingly misleading for altitude. In some parts of our area, such as the steep cliffs of the Weisse Wand near Schnellzughöhle (as seen in the photo at the top of this page), altitude is important for route-finding so GPS becomes surprisingly much less useful for re-finding locations. Before you use @@ -71,7 +70,7 @@ There is more about GPS altitudes in Olaf's article on GPS i

Without GPS we need an old-fashioned survey location using fixed points with a minimum of two bearings on fixed landmarks (see taking bearings - page for how to do this and for pictures of the various peaks we use). + page for how to do this and for pictures of the various peaks we used to use). This is now a forgotten skill.

Anything which gets a number (e.g. 2018-ad-01) should eventually be linked into an existing surface survey. The number (on a metal tag) will be attached to the cave @@ -125,15 +124,5 @@ best are surface surveys taking a short route from these points.

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