Jump to content

Newbie ?: GPS accuracy


Recommended Posts

36 minutes ago, shirleysnh2004 said:

I have both a Samsung G9 w Geocaching app uploaded and a Garmin GPSMAP 66i.  Can anyone tell me if one or the other device is more accurate when searching for cache?

 

I've only discovered geocaching since last July 25, so truly a newbie with no one close to buddy up with me on these adventures.

I haven't used those particular devices, but the last time I took coordinates for a new cache listing, I used both my Android device with an app that averages coordinates over time, and my handheld GPS unit that averages coordinates over time. The coordinates I got were virtually identical.

  • Upvote 2
Link to comment
2 hours ago, shirleysnh2004 said:

I have both a Samsung G9 w Geocaching app uploaded and a Garmin GPSMAP 66i.  Can anyone tell me if one or the other device is more accurate when searching for cache?

 

I've only discovered geocaching since last July 25, so truly a newbie with no one close to buddy up with me on these adventures.

 

There are videos in the Official App that may help.  Are there "Geocaching 101" Events in your area?  You can get great guidance there.

 

Hiking GPSrs and modern phones with appropriate Apps can get you in the general vicinity of the posted coordinates.  But it's not really "accuracy" that gets you where the cache is.  When you're about "30 feet away", the device has done its job and now you must understand the description including cache size and difficulty, the hints, look at the map, look at the area, and try to find the container.  Most any device can get you into a reasonable area to start a search, and a newer Garmin can show much of the cache info, "paperless".  And a phone (App or web site) can show you where the icon is on a satellite map -- which may not be all that accurately placed by the Cache Owner.  But you can sometimes look at the map and even stand right where that icon is.  You then need to search the area, because you're almost never standing on the cache when at "0 Feet" from it.

 

The Apps or the devices are tools that you must interpret, and understand how to use, and understand what they are telling you.  The compass will move, the distance will change, even when you're not moving.  This is normal.  You can select a Map screen, or a Compass screen, and you need to decide when to use which one.  If you have both a phone with Apps and a Garmin, you've doubled the amount of stuff you'll need to learn, because they will work differently.  Add to that the possibility of having to switch between street routing and direct routing, and it can get confusing.

 

Anyway, the "accuracy" (depending on nearby tree cover or buildings) will often be suitable enough for Geocaching, whichever device you use, or use both for the functions each does best.  Modern devices are accurate enough, most any of them.  But the cache hunt tends to be beyond accuracy.  :cute:

 

Edited by kunarion
  • Helpful 1
Link to comment
4 hours ago, shirleysnh2004 said:

Can anyone tell me if one or the other device is more accurate when searching for cache?

 

When they are used in an ideal environment, there should be no difference. But when you are finding a cache in the woods, the story is usually the opposite. A phone will stop working properly, but the dedicated receiver with a more sensitive antenna will continue its job.

  • Funny 1
Link to comment

Most modern consumer grade GPS receivers, both dedicated and smartphone, when operated in the best possible conditions, are capable of reporting their current position to within about 15 feet. Of course, this will vary based on the actual hardware used and ambient conditions when used.

 

Regarding Geocache Posted Coordinates, please always remember:

 

1. The device used by the person who captured the posted coordinates could have been 'off' by 15 feet or more, AND

2. The device used by the person searching for the geocache may also be 'off' by 15 feet or more, AND

3. ANY satellite imagery or other map used to determine what is located at the posted coordinates will ALSO be 'off' by an undisclosed distance

 

This all adds up to easily 30+ feet of device error under the best circumstances, and any map used may also mislead you, although unintentionally.

 

As stated above by kunarion, most veteran geocachers will put the GPS device away once they are within about 20-30 feet of ground zero, and then start using their experience, and 'geosense' along with the geocache description and any available hints or tips to find the actual geocache location.

 

The more you find, the better you will get at 'making assumptions' about potential hiding places based on the surrounding terrain, but this can also get some veteran geocachers into trouble when the geocache owner has been thinking 'outside the box'.

 

It is all part of the game we all enjoy immensely!

  • Helpful 1
Link to comment
4 hours ago, Viajero Perdido said:
5 hours ago, arisoft said:

A phone will stop working properly

A phone loaded up for offline caching - with a suitable app - will continue working properly in the woods.

I don't think arisoft was referring to online vs offline. I think arisoft was referring to areas with poor GPS reception, where a phone (or basic handheld GPS unit) might not get a GPS lock to establish its location with any accuracy, but a better handheld GPS unit ("with a more sensitive antenna") may get a GPS log.

Link to comment
47 minutes ago, niraD said:

I don't think arisoft was referring to online vs offline. I think arisoft was referring to areas with poor GPS reception, where a phone (or basic handheld GPS unit) might not get a GPS lock to establish its location with any accuracy, but a better handheld GPS unit ("with a more sensitive antenna") may get a GPS log.

 

That's what I also thought.  For most caching trips, I bring my iPhone 8 and Garmin Oregon 750t, and use each device's advantage.  I can do Waze to get to a cache parking lot, for example.  If I'm getting into the heavy tree cover, I'm probably already using the Garmin, so I don't know a lot about reception vs. accuracy on both devices.  But when the GPS is struggling to find a signal, the hunt can get tough.  The readings get jumpy.  Even then, I don't rely on "accuracy" as much as gallery photos, logs, hints, and what little Geosense I have.

  • Helpful 1
Link to comment
13 hours ago, Atlas Cached said:

1. The device used by the person who captured the posted coordinates could have been 'off' by 15 feet or more, AND

2. The device used by the person searching for the geocache may also be 'off' by 15 feet or more, AND

3. ANY satellite imagery or other map used to determine what is located at the posted coordinates will ALSO be 'off' by an undisclosed distance

 

This all adds up to easily 30+ feet of device error under the best circumstances, and any map used may also mislead you, although unintentionally.

 

There is another error to consider.  When converting positional error from GPSr (circular) to Map (XY) coordinates another error in introduced.  The GPSr determines a waypoint’s true position with an estimated positional error (EPE) that results as a circle about a point.  When expressing this waypoint using XY coordinates the result is a square bounded by the limits of the EPE.  This increases the search area by 27.4%

True Position Change.png

  • Funny 1
Link to comment
5 hours ago, Atlas Cached said:

While true,  I doubt most geocachers are going to consider this formula while Geocaching.

 

I always use to the circular way. Newer used the rectangular one.

 

20 hours ago, Viajero Perdido said:

A phone loaded up for offline caching - with a suitable app - will continue working properly in the woods.

 

I have newer used offline mode when geocaching in the woods.  I do not recommend to use offline mode because the GPS-A receiver used in mobile phones works better with cell reception. More details here: https://en.wikipedia.org/wiki/Assisted_GNSS

Link to comment
1 hour ago, arisoft said:

I have newer used offline mode when geocaching in the woods.  I do not recommend to use offline mode because the GPS-A receiver used in mobile phones works better with cell reception. More details here: https://en.wikipedia.org/wiki/Assisted_GNSS

Well, sure. If you turn off your cell/data connection, you're back to GPS with no assistance from the internet. But phones do have real GPS receivers, and can work without the assistance. And their accuracy in that mode should be fine for geocaching.

 

But the smartphone battery lasts a lot longer when it isn't cranking up the power to the cell/data antenna trying to lock onto a signal that it can just barely pick up deep in the woods. If I'm geocaching somewhere with an unstable cell/data signal, then I switch my phone offline just to preserve its battery.

  • Upvote 1
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...