New app: GPS accuracy settings

SMART Community Forum
1

Hi team,

Quick question regarding the new app version. We’ve noticed the new GPS accuracy settings in ‘Settings’. How does this relate to

a) the locations settings for the app on your phone (e.g. “Use precise location” and “turn off data and battery optimisation”)

b) the GPS accuracy settings you can adjust on SMART Desktop within Configurable model > Device Settings > Profile details > (e.g. “Sightings Fix Count”, “Sighting Accuracy” etc)?

Thanks

2

Hi Lisa,

“Precise location” means the location from the GPS, as opposed to “Course location” which is from WiFi networks or cell towers. It’s the one we always want.

The accuracy in Settings specifies the maximum allowed value for GPS reported accuracy. For example, if the GPS says its accuracy is 90 meters and we have specified 80 meters here, then the location will be ignored. This value is a bit vague in my experience, but generally the worse it is, the lower the confidence we have in the quality of the reading.

The “fix count” is the number of readings to drop before using a reading. This is to handle warm-up, i.e. it takes a few seconds for the GPS to acquire satellites when it is first turned on. Also, some devices would report the last known location as the first reading, which could be long way off. In the recent versions, we ignore the fix count if the track timer is enabled. The track timer keeps the GPS on, so there is no point waiting for a warm-up.

Another area of interest is the “Maximum speed” concept - now tied to the Transport Type. This is useful for removing GPS outliers. Outliers are a consistent problem across all devices whereby readings may be dozens of kilometers (or more) off. Trimble recommended that we detect this is by looking at the GPS reported speed and ignore cases where it is clearly wrong. For example, a foot patrol with a speed of 500km/h. Outliers seem to be less of a problem when the device has an internet connection, because they can download an almanac which seems to help.

Turning off battery and data optimisation should no longer be required on the most recent versions. We have a new architecture which runs the GPS completely in the background, so it will not stop recording if you get a phone call or switch apps.

Cheers,
-Justin

3

Thanks Justin, that’s really helpful.
Can I clarify - if we have the accuracy set to low (say 5m) in the app then will it keep trying to locate until it achieves this accuracy, or will it more likely just ignore the location (thus leaving the coordinates blank when you upload your data).
So if we need high levels of accuracy (e.g. for a veg survey point) is the best path forward to do the following:

  • Set “Precise location” in phone settings
  • set GPS accuracy to low (e.g. 5m) within the app
  • keep “fix count” high so that it keeps trying until it achieves the desired accuracy OR have ‘track timer’ enabled

Let me know if I’ve missed anything out here in our effort to maximise GPS accuracy for point observations (not worried about tracks for now).

Thanks, really appreciate your help
Lisa

4

Hi Lisa,

The thing that will make the biggest difference is to have the track running - the frequency does not matter. Although please make sure you are using a newer device (Android 9 or greater). This will keep the GPS on all the time and therefore maximize its ability to be tracking more satellites.

It is important that the device has as clear a view of the sky as possible.

If you require survey-grade locations, then you will need more equipment to get differential capability. I have not looked into this recently, but usually there is set up required.

If you set the GPS accuracy to say 5 meters and the GPS cannot meet that requirement, it will appear as if there is no reading coming from the device. You will not end up with data with empty coordinates, because you will not be able to save those observations. As I recall you will get a pop-up complaining about accuracy. The devices we have tested are very bad at estimating the radius of uncertainty. Sometimes my GPS tells me it is within one meter and I can see on the map I am at least 50 meters off. Our recommendation is therefore to test your devices thoroughly to get an idea of how well they work. Note that even different models from the same manufacturer can be different. Also, more expensive is not necessarily better.

Cheers,
-Justin

5

Thanks, Justin, that’s really valuable insight. We’ll do some more field tests and probably see if we have the budget for an external GPS device. We use a mixture of Blackview and Ulefone rugged phones, all Android 10 or above but we’re operating in challenging terrain and vegetation so we’re going to need something that is specifically designed for GPS alone. any hardware recommendations welcome!

Thanks again