GPSr and Phone conflict?

[+colleda]

Two days ago I had a very odd experience while doing a maintenance run on my Sand Island PT series.

GC478YV

Knowing where I had placed this one I went looking but could not find the spot much less the cache. I had my Motorola G4 phone with me as well as my Etrex 20x. I didn't have the cache coords loaded in my Etrex. I fired up the phone and, using the GC app started searching for the cache. There is tree some cover small, mangroves and others but was finding nothing. I assumed that the phone wasn't playing fair so I decided to enter the coordinates into the Etrex. When I did this it showed GZ 134m away. The phone was also indicating this distance on the coordinates page yet, on the navigate page was showing less than 20m. Strange.

I started off to where the Etrex was indicating and the further I went the more I thought that it was totally wrong. I went back to navigating with the phone. After about 10 minutes I had the phone down to 3m-4m. The ground at the indicated GZ was completely bare except for a dusting of leaf fine litter but was right at a pair of trees about 40-50cm apart, it looked familiar. My foot (clad in wet suit booty) casually scraped the ground and immediately exposed the to of the cache container at ground level. This was not where or how I had placed it September last year. It had had two finds since and no DNFs.

In that time the area and GZ has completely changed but with no clues as to how. When I placed the cache, between the two previously mentioned trees it was above ground level under some prickly pear (a type of cactus) and among some long grasses. There is now no sign that the prickly pear was ever there and all ground cover vegetation has gone. The cache was about a foot or so away from where I had placed it. Hmm. How did it come to be at ground level? There was no mention of anything untoward in the logs. From memory there was quite a bit of prickly pear all over the area but its all gone (except for a single small 10cm leaf(?) that appears to be the start of regeneration. Maybe it was killed off by salt water from storms or cleared by a volunteer Landcare group (Prickly pear is a declared noxious weed in Australia). This sand island has a height of about 1m at most.

Back to the phone and GPS. I still do not understand how the phone app was indicating GZ correctly but its distance estimate as well as the GPSr's was so wrong - 134m. I last used the Etrex in Miami 27/2 and it was working fine but since my return I noticed a couple of things had changed since then, most notably the main menu screen was arranged differently to what it was in Miami. Would flying through earths magnetic field upset it? I hadn't used it since I got home except to put new batteries in.

Any suggestions?

 

 

[+barefootjeff]

Welcome to the Twilight Zone. You have crossed through a Dimensional Barrier and everything is slightly different here.

 

I doubt flying through the magnetic field would do much, but with a large change in location since it was last turned on, there may be some cached values in its position calculations that need to be flushed, which might take a while.

 

Your experience reminds me of this log on an old cache not far from here:

 

Quote

Found it

07/01/2014

Parked at the trail and the gate to the trail was open. It appeared council were in there somewhere to do some work. Found the cache easily and headed back to the car. Put the keys in to drive away and nothing... Nothing at all... Was this the bermuda triangle on the central coast? There was a semi trailer parked nearby and the though crossed my mind "did someone in there cut my wires, is this going to be a scene of a real life horror movie?"...

 

I tried to turn the ignition again and once again nothing at all. I haven't had problems like this with the car before. It's always been reliable. It had been working fine all day and I hadn't left anything on to allow the battery to go flat. It was time to check the engine bay.

I turned around looking at the semi waiting to see movement from someone in there, but I couldn't see anyone. I went to my bag and pulled out my bush knife (in clear view of the semi - just in case). It was the only deterrent I had from a possible what seemed to be calculated attack.

 

With knife in my back pocket I checked the engine bay. Nothing seemed wrong or out of place. Back to the ignition I went to try turning the key once more, hoping i might be able to hear a sound which could lead me to the problem.

 

The engine clicked over, as if nothing had ever been wrong! What had happened? I have no idea.. Was it some sort of evil magic doing from someone hiding in the semi? Had my knife really acted as a deterrent somehow? I wasn't hanging around to find out! I got out of there quick smart!!!

 

Thanks for this hide and the unexpected adventure!!
TFTC cheers

 

UPDATE - Another cacher has contacted me suggesting that I had a "Wolf Creek" moment. Upon reflection that was exactly what I had!! Another worrying thing which happened at the time and which I worked out afterwards was that both of the clocks I have, 1 on the dash and 1 on the stereo, showed the incorrect time after the incident. They were both an hour and 45 minutes slow.. It had only taken me 15 minutes to get to the cache and back again and the clocks were both correct before I left the car. Had I really been gone for an hour and 45 minutes? If so what happened in the hour and a half I can't member?

 

Please take care at this cache. It appears I may have been lucky to escape this one unscathed!!

 

[+baer2006]

1 hour ago, colleda said:

Back to the phone and GPS. I still do not understand how the phone app was indicating GZ correctly but its distance estimate as well as the GPSr's was so wrong - 134m. I last used the Etrex in Miami 27/2 and it was working fine but since my return I noticed a couple of things had changed since then, most notably the main menu screen was arranged differently to what it was in Miami. Would flying through earths magnetic field upset it? I hadn't used it since I got home except to put new batteries in.

Any suggestions?

No solid suggestions here. barefootjeff mentioned the long distance from the device's last sat fix, which all by itself should lead to a longer time to get a new fix, but not to erroneous readings. But it's all in the software, which may have a bug or two . Every once in a while, my GPSr (an Oregon 700) is way off after I switch it on, and doesn't seem to come towards the actual position. I usually switch it off and on again (standard procedure for any misbehaving electronic device ), and the issue is fixed. But there was one incident, where the GPS completely "freaked out". All of a sudden, it started drifting away, until it was about 300 meters off. Restarting didn't help, and I thought that it was terminally broken. I continued caching with my phone, looking at the GPSr every few minutes (hope never dies). And after about 20 minutes or so, it started to drift back towards the true location, and quickly reached its usual accuracy. The problem never occurred again. Moral of the story: Sometimes electronics behave weird. Don't think about it too much .

[+barefootjeff]

6 minutes ago, baer2006 said:

Moral of the story: Sometimes electronics behave weird. Don't think about it too much .

 

Unless you're the engineer who created it, in which case please think about it a lot.

[+fizzymagic]

I seriously doubt that the phone was interfering with the GPS unit.  Rather, I think there was a common error.  The official Groundspeak app frequently lags the distance to the cache by up to a couple of minutes.  The GPS in the phone is updating the coords but the app does not reflect that.

 

There is no way to know for sure, but it seems possible that both the GPSr and the phone  experienced a multipath or similar error, but the phone just didn't update the distance displayed, although it did update the coordinates.  I've had this happen to me multiple times; I usually have to restart the app to fix the problem.

 

 

[+colleda]

I'm familiar with GPSrs taking a while to settle after changing continents.

In this case the phone was in conflict with itself i.e. navigation was working just fine but the coordinate "page' was 134m off.

Also, I turned on the Etrex when I started my paddle by kayak) and at that time I reset the trip meter. It had been on for about an hour which is, usually, plenty of time to lock in satellites.

I'll have to go back again soon to scout the island for another spot and I'll check it again.

[+arisoft]

7 hours ago, colleda said:

I fired up the phone and, using the GC app started searching for the cache.

 

When you put on any GPS device it is possible that the position calculations converges randomly to a wrong position and it will stay there until you move enough.

 

Wikipedia: " When the GPS antenna is moving, the false solutions using reflected signals quickly fail to converge and only the direct signals result in stable solutions. "

[+ecanderson]

I gave up on the gc.com Android app a while back for a couple of different reasons.  An experience similar to yours where the phone internal location data wasn't being reflected very quickly in the app was one of them.  One other was the inability to do a simple waypoint location average, which is part of best practice for placing caches.  All stuff I no longer have problems with when using a 'better' geocaching app on my phone -- and while I don't need to use my phone often, when I do, it needs to get the job done. 

 

As to your other question .. " In that time the area and GZ has completely changed but with no clues as to how."

I think the answer to that is in the name of the cache.  There are islands that I visit that are protected by mangrove and other vegetation such that I never see any difference from year to year.  There are a couple of others that look different on every annual visit.  Ma Nature gets her way now and again.

[+humboldt flier]

Sit them down in a room and have them resolve their conflicts as grownups should ... hmmmmmmm 

[+funkymunkyzone]

6 hours ago, humboldt flier said:

Sit them down in a room and have them resolve their conflicts as grownups should ... hmmmmmmm 

An intervention, yes!