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rragan

GPS accuracy

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Today a user in our Geocaching FB group lamented that Cachly was not as accurate as the old, now retired geocaching.com app. She also cited this log as an example of the issue. https://www.geocaching.com/seek/log.aspx?LUID=82f054ba-14d1-4f38-8b63-540cc2cf9dee

GPS accuracy is a difficult thing influenced by lots of varying variables. 

Apple provides a lot of controls around GPS accuracy: https://developer.apple.com/library/content/documentation/Performance/Conceptual/EnergyGuide-iOS/LocationBestPractices.html

I'm curious what settings/adaptations Cachly uses.

See also this thread about how the classic app GPSr performance was superior to the new Geocaching.com app. http://forums.groundspeak.com/GC/index.php?showtopic=341639

it sounds like the Classic Map might have been using very fast GPS updates to the detriment of battery. 
Smartphones seem to take awhile to settle down after jumping out of the car - likely because they take readings differently if they think you are driving. I think accuracy is damped down to avoid twitchy nav instructions as satellite views change rapidly, unlike when walking. I often see 1-3 minutes for the iPhone app to settle down after hopping out of the car while GPSr users are off and running.

 

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Accuracy can be greatly effected by a number of factors as you said. With each new iPhone that has come out the GPS chip has been more accurate, so if she was using an old iPhone 5 it could perhaps having worse accuracy. However, I have never seen issues with accuracy and many users have commented about how excellent and accurate Cachly is.

You can tap the current user location and it will show what accuracy you are getting from the GPS. I just tested it and was getting +/- 5 meters.

Cachly uses MKMapView location updates for the green current location indicator. We also use the standard CLLocationManager with kCLLocationAccuracyBest and kCLDistanceFilterNone for various places in Cachly. These are all turned off on non-map screens to save battery.

It would be hard to know specifically why that user felt that Cachly wasn't accurate, but if they were comparing it to a GPSr then it would be no comparison. The chip in the iPhone cannot compare to that.

52 minutes ago, rragan said:

I often see 1-3 minutes for the iPhone app to settle down after hopping out of the car while GPSr users are off and running.

I haven't seen this either, but I guess I have never hopped out of the car and gone running for a cache. My caching involves helping the kids get out of their car seats and getting them ready to go before we can go looking. :)

What iPhone do you use?

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Make sure Cachly is left open and showing a navigation screen — as Nic says, to save battery it only updates the location while navigating.

If you start navigating a few kms from the cache while still in the car, you should be pretty ready to go —seconds rather than minutes from my experience.

But at least with the current technology, a dedicated GPSr unit will always beat a phone — particularly if the GPS conditions aren't ideal (like being inside a metal container!)

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19 minutes ago, barefootguru said:

as Nic says, to save battery it only updates the location while navigating.

No, not only while navigating, on any map screen. So the live map, Offline map, navigate map, will always have Location Services turned on.

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As a former Geosphere user, I noticed no difference in accuracy on my phone when I switched to Cachly.   

Not related to caches, sometimes when I open Google Maps the GPS thanks forever to zoom in our has a huge radius. Other times it's right on the money quickly.  Depends on many factors as mentioned. 

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I did some caching in New York City and Boston least week. Most of the time Cachly seemed quite accurate. At times it was off but there were also times when checking my location on Google Maps could be a block of too.  It still seems to me like more of a phone limitation than a Cachly limitation. 

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Any GPS in NYC as well as other areas with tall buildings will struggle with what they call multi-path signals. I don't think a phone is any more susceptible to it than a traditional GPS but I'm not a GPS expert.

In my informal use of both an iPhone and a traditional GPS (Oregon 700), being used at the same time is the accuracy difference between the 2 is no different from the accuracy difference between 2 folks using a traditional GPS standing side by side. 

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On 3/30/2017 at 11:11 PM, rragan said:

I often see 1-3 minutes for the iPhone app to settle down after hopping out of the car while GPSr users are off and running.

 

This is pretty typical of all GPS devices when turned on.  You have to remember that most phone apps turn off the GPS chip when you are not actively navigating or viewing the map, in order to save battery.  When I turn on my Garmin, it will take up to a minute to find the sats and determine it's location. The initial reported accuracy will be something like 90 feet or so.  Over the next 1-2 minutes, the accuracy will fall to 2 meters or so. I have used quite a few apps on my wife's iPhone 6 and my Android phone, and the behavior is the same.  The difference is that with my Garmin, the GPS is active whenever it's powered up.  On our phones, the GPS does not go active until we call up the map or compass or select 'Navigate' to the target. And it will take 1-2 minutes to sync up and take a few readings to get it's position and accuracy down. And then with any of our devices, the magnetic compass is useless until we exit the metal automobile.

Try setting your phone to Navigate on the map or compass screen 2-3 minutes before you arrive at your parking destination.  That will give your phone GPS time to acquire and settle by the time you exit the car.

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