The android's distanceTo() and distanceBetween() function gives results when I reach the destination lat and lon. But I need to cover the case when latitude and longitude may not be changed (e.g. if I walk in the street with high buildings around, enter the building or walk short distance by taking more turns). For those conditions how to calculate distance in android?
When I was searching through stackoverflow others answers, I gone through here.
I tried the following answer. The code is good and fine but when I tried to calculate distance by that code everytime it gives a constant value even when I am not walking.
Please help me in calculating the distance between two points
When you enter the building you have GPS lat/long, but after that it will not change because there is no GPS coverage. So, question is how to handle such a case, having just last position. I would approach that interesting issue this way:
Use WiFi networks info for location as well (not just GPS).
Use sensors. You have orientation and accelerator sensors. I remember some phones having feature of number of steps counting (I had that on SonyEricsson without GPS).
Accelerator sensor may give you info if person is moving and help you to count the number of steps (you need to take some average step distance value estimate). You can easily conclude if person is in the elevator, and if he is going up or down, and roughly estimate number of floors.
Orientation sensor may give you info about direction of movement change (turning around the corner).
GSM signal strength based location. NeighboringCellInfo from android.telephony gives you information about RSSI (Received Signal Strength Indication) for cells around you, but for accurate calculation of the position (approx 50 m precision) based on triangulation you need exact position of Base stations (which you cannot get without support from the operator).
It is understood how inaccurate such estimation may be, but I see no other approach.
In any case, stuff for lots of fun exploring/developing.
Related
I'm getting negative Altitude value even when I'm on 6 storey building . I initially thought my code was wrong, so I've downloaded couple of apps from play store. Even it is showing negative value.
My location is
Chennai, Tamilnadu, India
Have you tried looking at this? I'm not an expert on GPS, but the two points in the answer here are likely to be the issue.
Android: How to get accurate altitude?
Your device is getting poor GPS results for some reason, possibly due to hardware limitations or firmware bugs. Contact the device manufacturer for assistance.
I've just googled around a little bit and this is what I've found about Chennai:
Elevation 6 m (20 ft)
The first thing that pops in my mind is that this is average elevation, which probably means that there are some parts of the city way above that, and also some parts that are below the sea level, even by 10-15m (which is roughly the height of the 6th floor).
This, combined with high margin for error of GPS altitude measurement (+/- 15m), might have resulted in your seeing the negative altitude.
I might be wrong though, this is just my initial idea. You can test it by climbing a nearby hills or mountains, such as [according to google]
Pallavaram Mountain.
GPS readings of altitudes aren't always accurate and have an error within about +/- 15 meters (50 feet) 95% of the time. GPS depends on clear and unobstructed view or it cannot make accurate range measurements to the satellites and hence the error.
So I would say to take the GPS readings with a grain of salt.
I am not sure what you plan to use the data for , but I would suggest you to normalize the readings you get over a period of time and use it.
Here's the source
Usually map data provides the average altitude levels of a given region, you can perhaps account that as a base value and compute relatively accurate altitudes.
I'm developing iOS/Android app that tracks mileage user has driven in his car.
Even though the task seems pretty trivial, there are 2 problems:
1) Mileage is not accurate comparing to car's odometer. (OD-10mi, App-8.5mi)
2) When user stays still outside the car, mileage keeps accumulating (it can add up like 4mi within 30 minutes.)
Is there any "easy" fix for that without adding complicated filtering, etc?
There are two small but significant things you can do:
For each GPS sample, check its accuracy. If it's over some threshold (say 20 meters) - ignore it.
Add a method that detects if the mobile is static or not. You can do it by reading the device's accelerometer - if the delta between two readings is bigger than some threshold - the car is moving. If it's too small - ignore the GPS. You'll have to try some values until you find the right threshold/
For question 1, vehicle odometer, in the US, are only required to be within 5mph of the actual speed at 50mph. My experience shows most vehicles are more erroneous than the law requires. That 10% difference could easily become the 1.5 miles you saw.
Vehicles odometers are allowed to over estimate in europe by 7%.
My car has about 3% over estimate.
There are simple solutions, that work for cars, that have been posted here on Stackoverflow multiple times, including by myself.
There is no simple solution for pedestrians.
Answer to question 2: problem certainly comes from the accurary of the GPS location.
Android Location object comes with an estimated accuracy for the given coordinates.
Suppose you stay in absolute position (0,0) without moving. The android device GPS could produce the following Locations stream:
(1,1) with an accuracy of 2m
(-2,3) with an accuracy of 5m
(0,0) with an accuracy of 1m
etc...
If you just keep adding the distances between the successive Locations, the sum will indefinitely increase, although you don't move.
One solution could be that you take into account new Locations from the stream only if their accuracy is small enough compared to the distance to the last location.
I a trying to create an application that will be able to guide people in a city, with points of interest. For this, I need the better accuracy I get, in order not to place POI where there is nothing...
To do this I use droidAR (it gives me a radar, and I can place my POI thanks to their coordinates). But the accuracy is so bad I can't see how this can used.
For exemple, to determine if I a close to a POI, I calculate the distance between it and my GPS position. It can be that, with a 10 meters accuracy given by Android when I place the POI, it is then 80 meters away when I try to find it.
SO I looked forward to find another position systems, I found :
skyhook, which is supposed to give a more accurate position. With this, I took 1000 points and checked their distance to the last point, it is always moving and it was sometimes 300m away, so it seems even less precise. Maybe anyone could use it successfully ?
someone told me to use DCM algo (Direct Cosine Matrix), that can give me an accurate relative position (no problem for my use cases to do every positioninf relative to a start point). Some drones are using it, it could reach 1 meter accuracy. But I couldn't find any implementation or help with Android.
Did anyone succeed into using the android GPS with accuracy ?
Either your android phone has a bad GPS device, or more probably you are doing something wrong. you can set a POI in city aprox. 5m acuracy, sometimes 20m. that is sufficient. check it with another GPS app that allows setting a waypoint.
In your app you could concentrate on the 95% GPS accuracy. There is nothing better than GPS (espcecialla yon a mobile phone), the other methods you described are for short time assistance to GPS, but they will not work good for pedestrians, they are made for vehicles (vehicles move straight most of the times, they cannot change its direction so fast like a human does).
Your problem is not the GPS location accuracy, it is the augmented reality projection of droidAR.
I am trying to implement a fitness app that can keep track of the running speed and running distance in Android.
It looks like I can either use GPS or Accelerometer to calculate these information.
Since a runner may put his phone in hand, on the shoulder or in his pocket, my first intuition is to use GPS to get locations and calculate running speed and running distance. But recently someone telled me that I can also use Accelerometer also does that.
My question is: In Android, which approach is better to calculate running speed and running distance, GPS or Accelerometer?
I suspect that pedometers are based on accelerometers because accelerometers are cheaper than GPS to use. in fact I think a lot of pedometers don't even try to measure distance. just acceleration jolts which equal steps. and then if they give you a distance measurement, it's by multiplying detected steps by a guessed or average step size.
GPS (if you are in an area where it works!) will do a very good measurement of distance. Even with a very cheap GPS receiver. All being basically OK, you should expect start and end positions to within 10m, and so for a 1km travel, you have 20m of uncertianty, which is 2% total distance uncertianty. This uncertianty goes down linearly with distance travelled (ie a 2km run will have 1% uncertianty, 4 km run will have 0.5% uncertianty, etc) the issues here will be with your realtime displays (GPS position jumps from satellite switching giving massive speed values, or immediate loss of signal giving a loss of all immediately displayable data)
I think that with a good accelerometer, starting from stopped you can continually integrate the signal to get speed, and continually integrate that result to get distance... I am just unsure what kind of accelerometer quality you get in any given phone? you may need to filter for noise or even garbage data.. And you also need to consider what accuracy it has. 20% accuracy in your sensor would make for a very bad distance tracker. So you might have to work with step counting and step size guesstimates.
perhaps a combination of both could work?
I'd be tempted to use the accelerometer data (either integrating or step counting depending on what will always work) to track speed and distance in short timeframe, then with much longer timeframe, generalised GPS data could be used to correct or scale that data from the accelerometer. Especially if you filtered/blocked GPS data based on uncertianty measurement at any given time.
Adding to what Julian said ... Normally GPS doesn't work under the roofs therefore for indoor gyms it will not work. Theoretically GPS signals are not bothered by clouds but when I was working on my GPS application, I had experience of unavailability of GPS signals in really bad weather (this might not be your case as no one will go on jogging in thunder storm :D)
Agreeing with Julian, you should use both GPS and accelerometer to build a reliable app for every condition.
The best results are obtained by using both of them, through sensor fusion. See:
Android accelerometer accuracy (Inertial navigation)
You will have accuracy problems if you just use either the GPS or a pedometer algorithm.
All pedometers I know are based on accelerometers. I guess, GPS is not precise enough for this stuff. It may say "no motion" while you did some steps, it's also dependent on the area you are trying to use it.
I have here a device which can give me GPS coordinates. The time interval I can define. I want to use it to calculate the average speed during driving or travelling by car. Actually I used a orthodrome formula to calculate the distance between two points and then divided it by the given time interval. By the implementation I followed this term. Unfortunately I could only find a German link, but I think the formula should be understandable in any language ;)
Unfortunately, using this formula and a time interval of 1 second gives very unprecise results. The speed while walking is between 1 km/h and 20 km/h.
So I wonder if there is a general reference on how to implement distance calculation between two GPS coordinates (I found something similar on SO) and particulary, which is the best time interval to update the GPS coordinates?
I assume that you're testing this by walking at a constant speed (I think ~5 kph is a normal walking speed) while measuring your GPS position once per second.
The variation that you're seeing in instantaneous speed (the distance between each measured point divided by 1 second) is either due to random variation in the measured GPS position or else you aren't taking your measurements exactly one second apart (or it could be both of these things).
I'm going to assume your measurements are being taken precisely one second apart. Hand-held GPS devices are much less accurate than advertised. While it's often claimed that the devices are accurate to within 10 ft. of the true position, this simply isn't so.
The best way to measure and report the accuracy of a GPS device is to leave it in a place where it can see the satellites and not be rained on, and record a few day's worth of data. You can then use Google Maps to plot the points - I've done this around my house and around the office, which is a good way to give you a sense of scale.
Obviously, if the devices were perfectly accurate, you would see all your measured points in one spot. Or, if the 10 ft. accuracy thing were true, you would see all the points in a little cluster inside a 20 ft. diameter circle.
What you see instead (with every GPS-enabled device I've ever tested) is a combination of relatively small positional scattering (on the order of a few tens of feet) occurring on a scale of a few seconds, and a longer-term "random walk" of the average position which might move 200 or 300 ft. in the course of a day or two. When plotted over your own house, for example, it might look like your PDA wandered over to the neighbor's house, then across the street, then down the street two houses, back towards you etc., all while jittering around 5 or 10 feet here or there like it drank too much coffee.
GPS can be more accurate than this. Surveyors use devices with much more powerful receiver sets (so they get a much more accurate read on the satellite signals), and they leave them in place for days at a time to average successive measurements. Handheld devices have cheap receiver chips and cheap antennas and have to deal with all kinds of signal interference anyway.
Your best bet is to do a running average to calculate your instantaneous speed. Instead of dividing the distance between the current point and the previous point by 1 second, take the last 5 distances between points and divide by 5 seconds (or whatever number of seconds you use). It's important not to just take the difference between the current point and the point 5 seconds ago and divide this distance by 5, as that would miss any non-linear movement.
Update: I noticed in a comment that you're using an Android device. Do you know if it has a built-in GPS receiver? Many (most?) Android devices don't, which means their GPS is not the triangulate-on-the-satellites version of GPS, but the guess-where-I-am-based-on-the-signal-from-the-cell-towers version. This is much less accurate positionally, as I'm sure you could tell from the snarkiness of my description. :)
GPS systems can yield instantaneous velocity directly, without interpolating positions. I read somewhere that the velocity reading is actually more accurate than the position reading. What device/system/OS are you using?
On Android, try the android.location.Location.getSpeed() method (along with hasSpeed()) in your LocationListener implementation.
Search on google for GPS SPEED ACCURACY, and you will find reports stating that speed calculated out of position-vs-time is ten times worse than just using the speed parameter coming right out from the GPS receiver. The speed parameter is not depending on position accuracy, but is calculated out of doppler (speed/frequency difference) from the satellite signals.
Good luck