Tape measure App

[commodore65]

Could an app be developed to use the gsensor and measure distances. I was thinking you could press a button to start a measurement move your phone press another button and we could see the distance in feet meters etc. is this feasable

[mugglesquop]

is this feasable

no.

go and get a tape measure and selotape it to the side of ur phone ;)

[Beherrschen]

It would get pretty complicated. Your phone would have to keep track of each and every different acceleration and the duration of that acceleration to then calculate out the distance traveled during each acceleration. Since we are human I highly doubt we can keep a constant enough acceleration to measure anything short. It does seem to me that the longer the distance being measured (maybe in a moving car as foot steps may throw the measurment off) the better chance there could be for accuracy as the small accelerations that would normally throw off the measurement would be less of a problem. (then again I am a physicist and not a phone programmer so I don't know how accurate the accelerometers in these phones are).

I bet something could be written to tell you how far the phone has been dropped... if you could keep the phone from rotating during the fall. The acceleration of gravity is constant and that would be an easy calculation that could just cut off as soon as the acceleration changes drastically (when it stops falling suddenly). Then again I am physicist not a programmer.

If someone wants to try feel free to ask me for a set of fairly simple equations or help with the math. I doubt most people that program will need that help though.

[mugglesquop]

i think the G sensor in the phone is a bit too "hit-and-miss" for this application, it would require a very fine tuned, high contrast sensor (most likely costing more than the phone!)

it you want to do a large distance, then u could use the GPS positioning, but yet again, wont be very accurate.

[not4you]

+ 1
i subscribe to this program but I don't believe is posible. I'm an architect so I'd strongly need it. you can youse GPS for outside mesurements and you can use SuperRuler for smole mesurements or distance mesurements.
http://www.pocketdevelop.com/index.aspx

[xboxhaxorz]

I dont think its that much of a stretch. Using tweeter i find the sensor is extremely accurate and sensitive. While i dont need the app, basically as he said press start and then start moving the phone left or right up or down and press stop.


However since the sensor is not made to do that, i could be totally wrong it it is not possible at all. Basically because the sensor is made to track tilt movements and not distances. Lol im basically debating with myself :)

[irus]

I dont think its that much of a stretch. Using tweeter i find the sensor is extremely accurate and sensitive. While i dont need the app, basically as he said press start and then start moving the phone left or right up or down and press stop.


However since the sensor is not made to do that, i could be totally wrong it it is not possible at all. Basically because the sensor is made to track tilt movements and not distances. Lol im basically debating with myself :)

it might work

[uniqueboy]

It's all relative, I can play teeter on a train!:)

[Beherrschen]

It's all relative, I can play teeter on a train!:)

If you're playing tweeter on a train traveling near the speed of light and I am at the train station watching you play teeter as you pass by, is the ball falling in the whole or the whole falling around the ball? Where was I going with this? Oh yeah would this tape measure have to account for time dilation? I mean the Lorentz equations are the most accurate set of linear coordinate transformations we have, right? As you move the phone time will dilate, lengths will contract and let's not even mention the rotation of objects from the phone's perspective... wait did I just mention it by stating that I wasn't going to mention it?

Like I stated before... it is completly possible to measure distance using nothing but acceleration information... beyond that the accuracy in your measurement will depend on the accuracy of the device measuring the acceleration(s). Of course you may have to get into the rate of change of you acceleration (the rate of change of the rate of change of the rate of change of your position) which is called jerk.

[Phexi]

it is completly possible to measure distance using nothing but acceleration information...

Erm guys, this is only a lil bit right ;D You can't measure a distance with an accelerometer... very well. As the word says, it measures accelerations... so if you walk 10 Meters to check the distance, your Device only accelerates the first meter when you start walking... when you walk with the same speed the accelerometer shows:

0 :)

(at this moment it has to know how fast your speed has to be when you accelerated in the first x seconds with x G's to calculate how many meters you walked within the x seconds till the -G starts when you stop ... almost impossible ;D )

[Davey101]

Absolutely 100% not possible, for any kind of practical purpose.

If the device could be held exactly flat, it would be just about possible to use acceleration data to make a guess at speed and therefore at distance... but it would be such a wild guess it would not be useful.

A visual estimate will always be better!

[Beherrschen]

Erm guys, this is only a lil bit right ;D You can't measure a distance with an accelerometer... very well. As the word says, it measures accelerations... so if you walk 10 Meters to check the distance, your Device only accelerates the first meter when you start walking... when you walk with the same speed the accelerometer shows:

0 :)

(at this moment it has to know how fast your speed has to be when you accelerated in the first x seconds with x G's to calculate how many meters you walked within the x seconds till the -G starts when you stop ... almost impossible ;D )


Seems like you told me I was only partially correct but then the second part of what you wrote seemed to agree that it possible (maybe not practical) to calculate distance traveled from nothing but acceleration information. It is possible to calculate distance traveled from nothing but acceleration (and the duration of each acceleration but that goes without saying since you must always know the duration of a motion to determine distance) information.

For example: If you have a situation where there is an initial acceleration A1 for t1 seconds, followed by a contstant speed S for t2 seconds, and finished off with another negative acceleration A2 for t3, then you have all the information needed to determine the overall distance traveled. During the first section of our travel the acceleration, A1, and the duration of that acceleration, t1 are can be used to calculate your total distance during that acceleration. A1 and t1 can also be used to calculate the speed you are traveling at the end of the initial acceleration, S. Use S and t2 to calculate the distance traveled during the constant speed portion. Then use S, A2 and t3 to calculate the distance traveled during the final accleration (even if your final speed isn't zero). Equations below:

Set 1: acceleration = A, velocity (speed) = V, distance = X, time = T, initial = i and final = f
starting with the assumption of constant acceleration then each successive equation can be derived by integrating the previous equation with respect to time.
A = A
Vf = At + Vi
Xf = (1/2) A (T^2) + Vi T + Xi

Set 2: also at constant acceleration with the same key as above.
A = (Vf - Vi)/T
V(average) = (Vf + Vi)/2 = (Xf - Xi)/T

Either set of equations can be used. They are basically the same set of equations. One derived using calculus (Set 1) and the other using conceptual ideas of motion (Set 2). With a little algebra both sets can be derived from eachother. If you add in an inconstant acceleration (jerk) then the equations become more complicated and I am not gonna derive them out here.

I am sticking to my is it possible but most likely not practical. Unless you came up with a way to maybe statistically ignore any little outlyer type accelerations... anyway, I am rambling. Feel free to let me know if you can't solve a problem like the one I stated above using those equations and I wll be glad to help.

[uniqueboy]

Seems like you told me I was only partially correct but then the second part of what you wrote seemed to agree that it possible (maybe not practical) to calculate distance traveled from nothing but acceleration information. It is possible to calculate distance traveled from nothing but acceleration (and the duration of each acceleration but that goes without saying since you must always know the duration of a motion to determine distance) information.

For example: If you have a situation where there is an initial acceleration A1 for t1 seconds, followed by a contstant speed S for t2 seconds, and finished off with another negative acceleration A2 for t3, then you have all the information needed to determine the overall distance traveled. During the first section of our travel the acceleration, A1, and the duration of that acceleration, t1 are can be used to calculate your total distance during that acceleration. A1 and t1 can also be used to calculate the speed you are traveling at the end of the initial acceleration, S. Use S and t2 to calculate the distance traveled during the constant speed portion. Then use S, A2 and t3 to calculate the distance traveled during the final accleration (even if your final speed isn't zero). Equations below:

Set 1: acceleration = A, velocity (speed) = V, distance = X, time = T, initial = i and final = f
starting with the assumption of constant acceleration then each successive equation can be derived by integrating the previous equation with respect to time.
A = A
Vf = At + Vi
Xf = (1/2) A (T^2) + Vi T + Xi

Set 2: also at constant acceleration with the same key as above.
A = (Vf - Vi)/T
V(average) = (Vf + Vi)/2 = (Xf - Xi)/T

Either set of equations can be used. They are basically the same set of equations. One derived using calculus (Set 1) and the other using conceptual ideas of motion (Set 2). With a little algebra both sets can be derived from eachother. If you add in an inconstant acceleration (jerk) then the equations become more complicated and I am not gonna derive them out here.

I am sticking to my is it possible but most likely not practical. Unless you came up with a way to maybe statistically ignore any little outlyer type accelerations... anyway, I am rambling. Feel free to let me know if you can't solve a problem like the one I stated above using those equations and I wll be glad to help.

For this to work we would have to stop the rotation of the Earth:D, but then there is not a stationary point anywhere in the universe, so I will never be able to measure the train I was on playing teeter. I always loved Newtons equations of motion especially the one A=A

[Beherrschen]

For this to work we would have to stop the rotation of the Earth:D, but then there is not a stationary point anywhere in the universe, so I will never be able to measure the train I was on playing teeter. I always loved Newtons equations of motion especially the one A=A


Actually if we are going special relativity on this problem then we also need to eliminate any form of gravity since special relativity only applies to inertial frames of reference. And since I am not about to break out the tensor mathematics of general relativity, then it would seem we are SOL in finding out what really did happen with your teeter game. :-(

Just remember: Things are the way they are because if things weren't they way they are we wouldn't be here asking why are things the way they are.

Anyone else having as much fun as I am with this thread?

[Beherrschen]

IDEA:

I have thought of a way to at least get a close approximation to this. I am not a programmer but it seems to me this should be possible. The area under the graph of acceleration vs time is velocity. Make a program that would plot the information acceleration vs time information on a graph in excel. Then, after the recording is finished, the program could go in at fixed intervals, turn the smoth graph into a point to point graph with straight lines from point to point (using the line of best fit feature in excel... assuming it is also in excel mobile...) and calculate out areas under the curve. Then you would have all the information needed, velocity and duration of each velocity, to easily calculate out distance. Now this would be an approximation and never be exact. But even calculators only give you Tailor Series approximations. The smaller the interval taken on the graph the more accurate the final distance would be. You could even make it work with an adjustable interval so the sensitivity could be adjusted.

To better explain my idea for manipulating the graph then picture a sine graph. On it's own it is a nice smooth wave looking graph that repeats every 2pi (don't want to look up the symbol for pi to type. just take 3.14159 = pi). Now imagine you marked a point every 0.5pi on that curve and then connected the points together with a straight line. You would end up with a saw tooth graph. Now what if you did that at every 0.2pi, or .1pi, or... you get my drift. The smaller the interval that you make a point and connect it the closer and closer you get to a good approximation of the original sine graph (much the way Archamedes used ever increasing numbers of triangles inside a circle to approximate its circumference and calculate pi). The advantage of doing this is to eliminate calculus and use nothing but algebra.

This could all be done without graphing and just having the program do the math tiself but why not let excel do the work? I could be way off and using excel this way may suck from a programming point of view, but this is how I would handle a lot of data if I were given a bunch of acceleration and time information. Making the sensitivity and accuracy changable by allowing the user to define how far apart to set the points could allow for some decent measurements. I think if done right even outlying movements (slight tilting of the phone or taking a step or two) could be negated by the approximation.

Let me know what people think. Even if this doesn't work maybe it will inspire a better idea!!