Using the accelerometer output, how do I determine if the user (iphone mounted on waist) is walking?
Looking for a good algorithm to determine if the user is walking to determine activity transitions- standing-to-walking or walking-to-standing.
please help.
Thank you for your time.
For a previous project, I tried calculating the magnitude of the acceleration vector, and just setting a threshold of about 2g, and that worked pretty well in testing. A typical (hardware) pedometer will ignore single jolts that happen more than about a second apart, which seems like a good way to filter out occasional movement that isn't "walking".
Additionally, you could automatically adjust the threshold by examining the data for a while.
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I have searched for hours now and still didn't find a definitive answer to my problem.
The scenario is this: the user throw an iPhone as high as he can and I want to measure the height that the iPhone has done.
I want to use the accelerometer with Core Motion and I successfully implemented a simple system that gives me the acceleration on the 3 axis. This is an acceleration though.
Based on my physics knowledge, the formula to calculate the maximum height is (V0^2)/2*g where V0 is the starting velocity.
I have the acceleration velocity though.
Any idea how can I convert the acceleration to velocity or directly get the velocity from my accelerometer?
I know it's not a completely programming related question, but I just want to have some help on this :)
First of all there is alredy an app that does exactly what you are up to: Send Me To Heaven. You won't find it in Apple's App Store because it never passed the review, guess why ;-)
As you stated you only have access to accelerations. h = v02/(2*g) is correct. To get the starting velocity v0 you need to integrate the acceleration numerically over the time. The trickiest part will be to find necessary and sufficient conditions to determine the time interval [t1, t2]. When did the acceleration phase start and when did it stop.
Another thing to consider is to avoid cheating users who just perform a rotation around there axis for a couple of seconds, then simulate the flying phase. There you might consider the landing phase too: when the user grabs the device you should register a strong deceleration.
However, don't expect this app to ever get in the store and at Google Play the competitors were faster.
Problems:
There's a number of problems physics impose on you (other than the velocity), to get the result.
The angle of the throw, relative to the direction of gravity. You cant know the relative vertical distance, unless you know this angle.
Orientation of reference throughout the throw (you cannot deduct the speed from the acceleration, from the device itself, unless you account for the changes in rotation while the phone accelerates).
However! You can decide to assume certain things, which will make these annoying problems go away!
Reasonable assumption:
The device is caught again, at the same relative height it was thrown.
This assumption reduce the problem to a much simpler one, in which we only really need to find the duration of time, where the device is in free fall, in order to determine the relative height of the throw.
All you have to do:
To determine if the device is in free fall, is relatively easy, since the total gravity would be near 0 m/s^2.
However, there's still one smallish problem to this, because the accelerometer is probably not located at the center of mass of the phone, so it will experience a constant acceleration (if the phone rotates around itself) in exactly one particular direction, throughout the free fall.
The maths of determining the height of a vertical throw, based on the airtime duration is left as an exercise to the reader :-)
simple question hard answer:
I'd like to be able to read if the device (and the user) is running/walking holding his device. I know that the iPhone accelerometer calculates acceleration so if the user runs at a constant speed, there will be no signal spotted.
Any help on that ?
I actually used to work on that...what you can do is to detect with the accelerometer and gyro the frequency of the movement. If you plot a chart, you will see a periodic behavior when you walk or run. Do some "field" testing and you could see how those frequency change between walking and running. It's pretty cool.
Try dynamic time warping (DTW).
First, you build a small "database" of motions that you would like to recognize.
Then, in your application you compare the current sensor readings with DTW to the ones in the database and pick the most similar one.
I'm wanting to figure out if a user is not moving at all, walking, or running using the iPhone. I'm not trying to implement a pedometer. I just want to know around about if someone is moving briskly, slowly, or not at all. I don't need mph or anything like that.
I think the accelerometer may be able to do this for me, but I was wondering if someone knows of any tutorials or example code that might be able to point me in the right direction?
Thanks to all that reply
The accelerometer won't do you any good here - it will only capture changes in velocity.
Just track the current location periodically and calculate the speed.
There are no hard thresholds for walking vs. running motion, so you will have to experiment a bit. The AccelerometerGraph sample code should get you started on how to get and interpret accelerometer data.
The Accelerometer is good, but if the user has an iPhone 4 or iPad 2 you should use the gyroscope.
CMMotionManager and Event Handeling Guide - Motion Events
Apple Documentation is the best example you can get!
People have a different bounce in their step between walking and running which can be measured with the accelerometer, but this differs between individuals (what shoes they are wearing, what surface they are upon, what part of the body is attached to the iPhone etc.), and this motion can probably be imitated by shaking the iPhone just right while standing still.
Experiment by recording the two types of acceleration profiles, and then use some sort of pattern matching to pick the most likely profile candidate from the current recorded acceleration data.
I have been doing a bit of research, but I cannot seem to find a way to determine small distances (centimeters and meters) using the sensors in Android or iOS devices.
Bluetooth appears too inaccurate and require more than one device, GPS only works over larger variations in distance, and small variations in rotation seem to make using the accelerometer nearly impossible.
Is there a method that I am unaware of that would allow me to do such a thing? I am familiar with Calculus, so using Integrals to determine distance based on changes in time and velocity/ acceleration is not a problem for me, I just do not know how to determine those things.
Thank you.
There's no sensor in these devices which is able to give you the desired accuracy without exterior help.
If your use case allows for a bit of external setup, here are some ideas:
You could use the camera and computer vision to calculate device movement. You could, for example, use ARToolkit to measure the distance to a visual tag fixed to a wall. In close distances you can get pretty high accuracy (mm) using this technique.
Another idea would be to measure the distance to a solid object, like a wall, by emitting a short audio signal using the speaker and measure the time until the echo arrives at the microphone. This would be more of a research project, though.
You CAN use the accelerometer to measure distance travelled
(if ONLY absolute displacement is involved).
Have the user hold the device flat and walk from pointA to pointB.
The user presses a "Start" button in ur app as he starts from A and
presses an "End" button in ur app as he reaches B.
Calculate the double-intergral of AccelX & AccelY seperately over time
between the 2 button presses. These will be distX & distY respectively.
Total displacement will be sqrt( (distXsquared) + (distY squared) ).
GoodLUCK!!
Regards
CVS#2600Hertz
Just as a thought experiment, you should be able to do this using a combination of the accelerometer and the compass on each device.
However, whether the accuracy of these sensors is enough for what you want to do...well I think you'd just have to try it.
I'm working on locating an iPhone device in 3D space.
I can use lat/long to detect physical location, I can use the magnetometer to figure out the direction they're facing, and I might be able to use the accelerometer to figure out how their device is oriented, but I can't figure out a way to get height of the device off the floor.
Specifically, I need to know if the user is squatting down, or raising their hand toward the ceiling (a different of about 2 meters/6 feet).
I posted a more detailed description of what I'm trying to do on my blog: http://pushplay.net/blog_detail.php?id=36
I would love any suggestions as to how to even fake this sort of info. I really want the sort of interactivity and movement that would require ducking and bobbing, versus just letting someone sit back and angle the phone -- kind of the way people can "cheat" playing with a Wii...
The closest I could see you getting to what you're looking for is using the accelerometer/magnetometer as an inertial tracker. You'd have to calibrate the user's initial position on startup to a "base" position, then continuously sample the sensors on a background thread to build a movement model. This post talks about boosting the default sample rate of the accelerometer functions so that you can get a pretty fine-grained picture of the user's movements.
I'm not sure this will solve your concern about people simply angling the device to produce the desired action, but you will have to strike a balance between being too strict in interpreting movements and allowing for differences in movement
The CoreLocation stuff gives you elevation aswell as lat/long, so you could potentially use that although there are some significant problems with this:
Won't work well indoors (not a problem for Sat Nav, is a problem for games)
Your users would have to "calibrate" (probably by placing the phone on the floor) each location they use!
In fact, you'd need to start keeping a list of "previously calibrated locations"... which could vary hugely just in one house (eg multiple rooms and floors). Could get in the way of the game.
Can't be used on moving transport (tranes, planes, automobiles... even walking) because elevation changing so frequently.
Therefore I'd have thought that using the accelerometer as a proxy for height is a substantially more preferable route than determining absolute elevation.
I am not intimately familiar with the iphone. But it might require a hardware add-on. (which you probably don't want to do). After thinking on this the only way I know how is through light or more specific laser. You shoot out a laser on the floor and record the time it takes to get back. It's actually not a lot to put this hardware together and I am sure the iphone has connections for peripherals. Unless osmeone can trump me, I say ther eis no way to do that with an image.