RTK future link - online edit of handbook/survey/gps.htm

handbook/survey/gps.htm

@@ -42,15 +42,29 @@ the GPS on the point. Don't build a cairn, they don't last for decades and we ha
 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). 
+  
+  <h3>Camera locations</h3>
+  
+<p>Even if you have no intention of using your location or recording a track, the camera in your phone will record locations of your photos which are extremely useful to future expeditions - for reasons which only become apparent when you yourself try to work out what someione did 10 years previously.
+  <figure class=onright><a href='/handbook/computing/l/camera-ne-track.html'><img  src='/handbook/computing/t/camera-ne-track.jpg' /></a><figcaption>Camera photo locations are not<br> on the track!</figcaption>
+</figure>
+  
+  <p>Your <em>camera</em> will use the same location settings as the rest of your phone, but sometimes with a bit of a delay. We have lots of examples of geo-located photos where the recorded location is alctually the location of the <em>previous</em> photo because someone has taken a quick photo but the phone hasn't had time after waking up to get a location, so it uses the previous one! And doesn't tell you!!
+    
+    <p>So when taking a photo of an entrance, always take one photo; delete it, and take another. This will give your phone a chance to get synchronised properly. 
+      
+      <p>ALSO: always take 3 photos of any entrance, the obvious one about 10m away, a scene-setting one from 20 or 30m away, but also a really close one of 3 to 5m away, so that we can see if rocks have moved around the entrance and also for a much better identification in future. If there is a tag, <em>always</em> take a close-up photograph of it so that the letters are readable.
 
   <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
+you can set it up for <i>averaging</i>, which used to give 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.
 </p>
 
+<p>Averaging used to be very important, but today (2025) we have so many GNSS satellites in the sky that ionospheric effects are the significant error. These change slowly over 5 hours or so, so avergaing for a minute or and hour does nothing useful. You would need to average over several days. The solution for a fast fix is <a href="handbook/computing/myphone.html#future">to use RTK</a>.
+
 <p>While the GPS is averaging 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