I made a simple GPS. app. for android, storing the route coordinates into file.
I'm confused, I got more onLocationChanged event when I stand in one place. The bearing and speed was zero of course in the Location when the event comes, but it Is interested, because I used 1 meter for minDistance when I registered the LocationListener. (the minTime was zero)
Are you sure that the values returned by getLatitude and getLongitude are identical to their previous values? Normal GPS is only accurate to within a meter or two, so it seems to me that random shifting of your location as perceived by your GPS sensor could be the problem.
You may be registering with more GPS satellites as your app runs and this may shift your position and reduce the error in all the times received from all the gps signals. Also, as you stand still position will become more and more accurate it is possible to get a gps signal accuracy down to cms see: http://atarist.home.xs4all.nl/geo/gps_accuracy.htm and wiki link on real time kinematic especially if you get a connection to a reference signal
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When we save coordinates gps in android , We know the gps is not precise
for example , Here the blue point is the real coordinates, the red points is the gps gets in several attempts
this is (not a real ) route, after we drawn the lines if you have (driven/walking/moved)
this is (other fake ) route which is much more fine,
is there some algorithm/code for get this result ?
As you said - you will get different readings even if the GPS is static, due to GPS errors, but that's not the whole story: When you move relatively slow, you're also getting those erros. There are few things you can do about it:
Filter out "bad" readings - when you get a location from the GPS, you also get the location's accuracy. Decide a threshold, say 20m and ignore any readings with worse accuracy.
Filter out close readings - If the distance between the current location and the previous location is smaller than some threshold (I'd suggest 10 - 20m) - ignore the current location and wait for the next one.
You can also use your device's sensors (like the accelerometer) to decide if your device is moving or not. You can see a code example here.
I am in need to develop an android app where the device will track the distance traveled while the user is in a moving vehicle. I am getting the GPS values at small interval so that I can retrieve the distance and sum them up. But the problem I am facing is, while the user is in the vehicle, the device is not getting a clear view of the sky. Hence, the GPS device cannot get values as frequently as I desire. Thus, the result produced contains huge fluctuations. I tried using the network provider, but that is even worse in this scenario.
It would be very much helpful if anyone can suggest me a solution to this problem.
Just put the receiver onto the inner side of the windshield, like all navigation systems do. This should give an acuracy of about 3-6m. (when SBAS correction is available in your location) or up to 10m if not.
If the receiver is not state of the art (combined GPS + GLONASS or BEIDOU) then you will have problem in cities, especially in urban canyons with location jumps up to 30m.
This is normal. To get correct result for a GPS application within a city you need advanced algorithms. Just summing up the distance between two consecutive locations is to primitive, this never works well. Distance calculation by GPS has be answered some times her at SO. Use the search engine, to get more info at that topic.
Of course, set the device to GPS provider only, with maximum precision.
Iam trying to calculate speed ( using distance/time). I know there getSpeed method on Location, but I tried it while driving and GPS on and it was not accurate at all My calculations were closer to reality.
Anyways, my question is , is there any way I can get speed using network location within a certain error range? Right now , it is throwing values like 100 km/hr and 5 km/hr for every location I get in the network and I am not if there is reliable way. I currently just make sure that whatever location I get from network is newer than the previous network location
Thank you
Since you already have a list of locations, my suggestion is that, filter your location data received from network.
Speed is one of the factor you can use to filter.
You may try other ways to filter, like points in the wrong direction or far away from your path.
Increase the frequency of your location collection.
"accuracy" value from the network location data. But be careful with this. Big value doesn't always mean bad location, and small value doesn't always mean good location. After filtered, you may calculate your speed again.
Hi i have one small problem.
I wrote an app in which i log lat,long and alt from gps.
Long and lat is quite ok but altitude is at the start more than 60m above correct one ( correct is ~275 but shows ~345).
During first 1-2 minutes of logging altitude is constantly getting lower and lower till it shows correct one ( 345-> 344 -> ....-> 275->275 and so on).
Can anyone explain it to me why altitude is getting better during the time and after some time it shows good altitude during rest of the walk/ride?
" it shows good altitude during rest of the walk/ride?"
I doubt that altitude is good on the rest of your ride.
altitude via GPS is known to be not very usefull. The error is about twice that of horicontal (lat,lon) error. Thats the reason why professional navigation devices additionally use a barometer sensor instead of GPS altitude alone.
The reason why it gets better, is that the averaging algorithm had more time to average the errors out. On my ios devcie and i my app, the altitude jumps so much that it shows some hundreds meters ascending / descending even when I am moving level at a lake.
But you always can check the value of vertical accuracy. Use the altitude only when it gets below 30m vert. accuracy.
In order to get accurate coordinates, a GPS system should listen to at least 4 sattelites of the GPS constellation. Also, those sattelites broadcast messages that are 30 seconds long.
Since most users nowadays have some level of ADHD, a 30 seconds time to get the first fix (and a further 30 seconds more for every other fix after that) would make many project managers and device designers scream. They also want your cell phone to divine where you are even with only two or three sattelites in view - theoretically possible, but you get results with poor accuracy doing that. With three sattelites you can get an approximation, but with only two you're no better than if you were using a compass and an astrolabe.
So that's what happens: your device doesn't wait to get the whole message from the sattelites, and keeps approaching a more accurate result as more and more of the GPS message pours through. After a while, some time after the first few messages, it gets the correct fix and its stops trying to guess your coordinates.
How would I go about tracking the distance a user travels? I don't necessarily care about storing waypoints, although that may be necessary to calculate distance anyway.
So far, I am creating a LocationManager and regsitering an onLocationChanged listener, and then calculating the raw distance between two points when the listener fires.
The problem here is that if I leave the app sit still on a desk for 10, 15 minutes, it will say I have traveled .5 miles. How should I go about checking for accuracy and determining which points to use?
Or, even better - is there an SDK or .jar I can just include in my project and call their functions to make this whole thing easier?
Thank you for your time.
I am not an Android programmer but have implemented this functionality in my own embedded processor with far less processing capability than anything that runs Andriod.
This is nothing to do with the accuracy of a fix as determined by the GPS. If you have a stationary GPS receiver with "perfect" visibility of the sky and plot its reported position over time then you will see it wander around the true location, moving some metres an any direction. If you accumulate the distance travelled, in very small steps, around the true position you will end up with the distance travelled apparently taking you to the moon and back.
You need to set a movement threshold that is greater than the position accuracy of your GPS fix, and then only add in the distance travelled when you are sure that you have moved from the point at which you added in the last movement step.
You can call getAccuracy() on the Location object it gives you to check the accuracy. If your app needs to be real accurate, you can only count values with a high accuracy.
You can also call getProviders() on the LocationManager to check to see if you're getting coordinates from wifi, gps, or both, and ask the user to use their gps if it's not currently turned on so that you get more accurate points.