Some resources say getLastKnownLocation() merely gives a location of some previous app's Location Change Listener.
But one thing I feel is missing from the conversation -- if the phone has GPS enabled, isn't this GPS tracking/updating as the phone moves? So if I call getLastKnownLocation(), isn't it getting the current GPS from the phone's constantly-updated GPS?
If so, then why do people warn against using it / accuse it of potentially getting a "stale" location? If the GPS is being tracked / updated, and getLastKnownLocation() makes a one-time grab of it's current position, what makes getLastKnownLocation() bad?
What am I mistaken about the Locations service or GPS?
The documentation says: Returns a Location indicating the data from the last known location fix obtained from the given provider.
Also, about the "out of date location": This can be done without starting the provider. Note that this location could be out-of-date, for example if the device was turned off and moved to another location. ("This" refers to getting the last known location).
Also, taken from LocationProvider docs:
Each provider has a set of criteria under which it may be used; for example, some providers require GPS hardware and visibility to a number of satellites; others require the use of the cellular radio, or access to a specific carrier's network, or to the internet. They may also have different battery consumption characteristics or monetary costs to the user.
if the phone has GPS enabled, isn't this GPS tracking/updating as the phone moves?
Well, it is, but not constantly. This has to do with battery consumption, if the phone was constantly updating the GPS location, the battery life would suffer a lot. The GPS location is usually updated when some app requests it. But even that request is not guaranteed to succeed. For example, suppose your going into a tunnel. Some application requests to update the GPS coordinates right before entering the tunnel and it succeeds. Now, you've entered the tunnel, which is 5km long. Most probably your device won't be able to get a GPS fix from the tunnel, so for the next 5km (at least) getLastKnownLocation() will return an outdated value, since the devices last known location was at the entrance of the tunnel.
What you could do is explicitly request to update the GPS location, that however might take some time and there are no guarantees that it will succeed.
You have the assumption "if the phone has GPS enabled, isn't this GPS tracking/updating as the phone moves". This assumption is incorrect. The GPS functionality takes up a lot of battery life so it should be used sparingly and almost certainly not all the time.
Related
I am developing an application where I want to use Fused Location Provider. But I have some doubts, and couple of questions.
When GPS is off and I set priority to HIGH, does that mean that the GPS will be automatically turned on, or not?
Can I set UpdateLocation with Fused provider with HIGH priority on demand to save battery at least a little bit?
How can I know what Fused provider is using (is it a GPS or a network provider)?
And finally
Is Fused provider really the best choice for android location? Are there any negative points about it?
What is your opinion?
Thanks in advance.
When GPS is off and I set priority to HIGH, does that mean that GPS will be automatically turned on, or not?
No, it will not be turned on automatically. But if you use SettingsApi, will prompt a dialog to user and gives information that GPS is must be turned on. If user accepts it, the gps will be active automatically. Check the SettingsApi
How can I know what Fused provider is using (is it a GPS or a network provider)
If you use fused provider api with SettingsApi properly. It will make adequate the required settings for current location request.
Is Fused provider really the best choice for android location? Are there any negative points about it?
In my opinion, before fused provider you must deal with directly providers(Gps, network) But fused just asks you, "how accurate locations you wanna receive ?"
As in here https://developer.android.com/training/location/index.html stated very clearly that, the Google Play services location APIs are preferred over the Android framework location APIs (android.location) as a way of adding location awareness to your app. If you are currently using the Android framework location APIs, you are strongly encouraged to switch to the Google Play services location APIs as soon as possible. So I hope you got your answer.
I made a testing application for Gps, Wifi and Fused Location Provider and testing it for 2 days. It's better because it uses both of them and most of the time it's the one most accurate. Also, Gps data is a very noisy data that causes jittering, to solve this low-pass filter or other filters are used. One of the most successful filter used to get most accurate results is Kalman Filter. FusedLocationProvider use this filter same as RotationVector which is a fused sensor combines hardware and software. RotationVector uses accelerometer, gyroscope(if available), and magnetic field sensor to get and filter positition and azimuth data.
Location.getProvider for Gps with LocationManager returns "gps", Wifi returns "network", and FusedLocationProvider returns "fused".
When GPS is off and I set priority to HIGH, does that mean that the GPS will be automatically turned on, or not
Anything other than "Battery Saving" turns Gps on if available. This settings available on my Android 7.1.1 phone. Setting for location was different on previous versions of Android on user's side. As a developer to enable using Gps you should set mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
PRIORITY_HIGH_ACCURACY - Use this setting to request the most precise location possible. With this setting, the location services are more likely to use GPS to determine the location.
Setting Priority also determines battery use level too.
Can I set UpdateLocation with Fused provider with HIGH priority on demand to save battery at least a little bit?
Yes, you can set interval of location request in addition to priority.
mLocationRequest.setInterval(UPDATE_INTERVAL_IN_MILLISECONDS);
mLocationRequest.setFastestInterval(FASTEST_UPDATE_INTERVAL_IN_MILLISECONDS);
How can I know what Fused provider is using (is it a GPS or a network provider)?
Location from Wifi never returns true for Location.hasSpeed() but Gps returns almost always true if you are outdoors. Also location.getExtras() have satellites tag which you can check for satellites which is only available for Gps. Speed may not be correct if you are walking or as far i've read so far, i haven't tried this on car, when speed it less than 5km/h it's not very accurate. I mean if you are using FLP and last location data contains speed info it's definitely from Gps.
Are there any negative points about it?
As of Android 8.0 and above there is location retrieving limit if you do not use a Foreground Service or get location on foreground while app is not paused for both FLP and LocationManager.
Also FLP requires GooglePlayService to be available on user's device and it should be above a particular version. 10 or 11 depending on which one you use. This can be trouble if you wish to publish your apps on a country, for example China, that bans Google Play Services.
The existing answers don't say why the FusedLocationProvider is better.
It is better because the API fuses from more data sources (sensors, wifi, context, history) in an intelligent and battery-saving way. Also, Google is always improving it by adding more data sources. If your app uses it, you get those improvements for free.
Hi i am working on a real time location tracking application where i have used Fused Location provider Api. I was able to get the location updates when the device is moving. But i was also able to get the location updates even if the device is stationary on a table when i am indoor. So I have calculated the distance between the last location and the current location triggered in Onlocationchanged event and checked whether the distance is less than 30 metres, to know the device is actually moving. But sometimes the distance i get is greater than 400 metres (indoor/Device is Stationary). How Can i ignore the onlocationchange event when i am indoor? Any suggestions are appreciated.Thanks in advance.
Unfortunately I don't believe there's much you can do about it.
The reason you see those updates with great changes it's because indoors, you won't get a GPS lock, so the device is relying on cell tower and WiFi hotspot triangulation to determine your location, and something around 200m to 1km is the best you'll get with this kind of technology.
A possible attempt to hack-around it would be to:
check the source and precision of the location update
use the activity recognition API to guess if the device really moved
but both are a hack, around the technology limitation and might not be as reliable.
I've got an app which sets up two location listeners (one for GPS and one for network) and then chooses the location from the best one available, which should be GPS. However, if GPS is turned on, it will always choose the GPS location, even if the person starts the app up indoors. This has led to the GPS location being used even if the last known GPS location is from miles away and the network location is actually much more accurate.
Is there any way around this issue or is it just something that will need to be accepted as an issue with using GPS & network? Is the standard practice just to assume that GPS is always more accurate even though it's possible that it might not be in certain instances?
If you are using the network provider to fetch the location they are not very accurate when compared to GPS. So it can be a good idea to fetch the accuracy of your position using network provider when you are indoors as GPS doesnt function well indoors and you can use GPS to get the location updates when you are outdoor.
You can use GetAccuracy() method of Location class and see for the value it returns. Let Say if getAccuracy() retruns 25 then you can leave this value wait for another gps value until you get the desired value. Remember the value it returns is the radius of the circle in meters.
I have re-read the whole documentation and as I understand, this API intelligently fuses the providers to give you an accurate result.
The Fused Location Provider intelligently manages the underlying location technology and gives you the best location according to your needs.
To my understanding, it will use Network and WiFi and GPS to give you a location. Now it is only logical to assume if one of those 3 is unavailable, it will use the remaining 2.
My problem is I'm testing my app to get Location when both WiFi and GPS are off. That will leave Location Service with the network provider only. But I'm getting Latitude and Longitude = 0.0
Long story short, either way I'm wrong in assuming that it will work relying only on network (no GPS, no WiFi) or there is something else I don't know or haven't read yet. Which of this 2 is my issue?
PS: my LocationRequest configuration is set to setInterval(30000) to setFastestInterval(60000) (30 and 60 seconds respectively, for each update.
I am using LocationManager to get the values of Latitude and Longitude of a user. These values are updated regularly to a database and find out the distance between two users basing on the stored Latitude and Longitude values.
Now,onLocationchanged() called very slow,some times get fast.while i'm waiting long time to proceed next process.When i 'm in indoor the Location search is very slow..
Is there any solution to this prob.pls give me a guide and example.
Please Accept My question as soon as give me a solution.
If you use network location provider, you will get location faster, but it will be less accurate (100-500m).
OTOH, GPS provider will be more accurate (10-20m) but it will take more time to acquire location as device needs to acquire GPS satellite signals. Sometimes it's not even possible to acquire signals, especially if indoor or beneath thick trees.
Well there are there types of GPS starts :
COLD start: takes a lot of time. The old GPS (satellite/time) data is practically useless.
WARM start : is when the GPS device remembers its last calculated position, almanac used, and UTC Time, but not which satellites were in view. You get the fix fairly fast.
HOT start : is when the GPS device remembers its last calculated position and the satellites in view, the almanac used (information about all the satellites in the constellation), the UTC Time and makes an attempt to lock onto the same satellites and calculate a new position based upon the previous information.
To emulate the warm start case all you have to do is connect to the SUPL network, which provides assistance data. Even cold starts can be converted to a warm start. To make sure that SUPL networks are available, make sure you are connected to the internet. In indoor cases no satellites are visible so getting an exact fix is tough without any assistance data. At least 3 satellites should be visible. Again SUPL networks come to the rescue.
Note that, various GPS chipset have different performances/algorithms and the triangulation time depends on the SUPL networks provided by your Network provider.
You can here more about this here
Good starting point is blog/project by Reto Meier:
http://code.google.com/p/android-protips-location/