GPS re org

handbook/survey/gps.htm

@@ -9,6 +9,8 @@
 
 <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>
 
@@ -28,8 +30,14 @@ otherwise with a restricted view of the sky, then choose instead a good
 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>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.  <h3>Calibrate/document your phone's capabilities</h3>
 
+<figure  class=onright width=20><a href='https://github.com/barbeau/gpstest#readme'><img width=64px src='/handbook/computing/t/gpstest.jpg' /></a><a href='https://github.com/barbeau/gpstest#readme'>&nbsp;<img width=64px src='/handbook/computing/t/F-Droid_Logo_4.svg.jpg' /></a>&nbsp;
+</figure>
+Install the "GPS Test" app, this one: <a href="https://play.google.com/store/apps/details?id=com.android.gpstest">GPS TEST</a> and check whether your phone is using SBAS "Satellite-based Augmentation Services", which is another name for EGNOS, the differential GPS system.
+You need to record if SBAS is in operation whenever you record the position of a cave entrance (and ideally whenever you take a photo too, but that would be unrealistic). [ Philip Balister takes a screen-shot of the GPStest screen whenever he want a proper GPS location. A notebook and pencil are also valuable adjuncts when looking at lots of entrances: use the timestamp on the screenshots to correlate everything. ]
+
+  
 <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.
@@ -75,10 +83,19 @@ 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.
+<h3 id="future">The future</h3>
+ <p> <a href="https://www.cavinguk.co.uk/info/locatingsurveys.html">Location fixing: How to obtain a fixed point for a cave survey</a> (2020) .Galileo High Accuracy Service (HAS) was due to become available in 2024, which would offer RTPPP for free around the world - but it's still not really working for most people. 
+   This is an excellent article and nearly all of it is still absolutely true, e.g.:
+   <blockquote>Keep the device very still. If the position shown by GPSTest slowly refines then stops updating within a minute or two, or shows only the last digit changing slowly, <em>then your device cannot be used for averaging</em>. A device with 1 metre accuracy still shows the 6th and 7th decimal place digits of the longitude and latitude updating every second or so (that is a roughly 10 cm wobble every second). Unless your device can actually do 1 cm accuracy, you should be seeing those numbers change! In general, this makes most phones unusable for this purpose"</blockquote>
+<p>Unfortunately RTPPP  has not actually caught on [2025] and it is still only available for experts and phones  supporting L2 and L5 frequencies have been slower to appear than we hoped. Read Wikipedia on <a href="https://en.wikipedia.org/wiki/Real-time_kinematic_positioning">Real-time kinematic positioning (RTK)</a>.
 
 <hr />
 <a href="newcave.html">Next survey guide page</a> - 'Base Camp: getting it in to the computer'<br />
+<br />
+<div class="text-box">
 <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>
+<a href="/logbookentry/2024-07-21/2024-07-21c">Photo GPS</a> - Is unreliable unless you follow procedure<br />
+  <a href="/handbook/survey/gps.htm_edit">Locating Entrances</a> - expo recommended methods (this page)<br />
+</div></body>
 </html>