Accelerometer distance

Question

I want to move objects on the iPhone screen (rectangle, circle, etc.) by moving the iPhone. For example, I move the iPhone along the X axis, and the object moves along the X axis. The same goes for the Y, Z axis.

How can i do this? Can I get an algorithm for this?

Thank.

PS: I’ve been looking for some time and it seems that this is possible with the help of an accelerometer.

Answer 1

You gain a position by integrating linear acceleration twice, but the error is terrible. In practice, this is useless.

Here is an explanation of why (Google Tech Talk) at 23:20. I highly recommend this video.

However, a gyro mouse may work for your application, see between 37: 00-38: 25 in the video.

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Answer 2

It’s not easy to do for sure. The accelerometer reports only acceleration, not motion. You can try (numerically) integrating acceleration over time, but you will most likely encounter cumulative errors that add up and lead to inadvertent movement.

Pseudo code, clearly unverified:

init: loc = {0, 0, 0} ; location of object on screen vel = {0, 0, 0} ; velocity of object on screen t = 0 ; last time measured step: t0 = time ; get amount of time since last measurement dt = t0 - t accel = readAccelerometer() vel += accel * dt ; update velocity loc += vel * dt ; update position displayObjectAt(loc) 

Answer 3

Why aren’t you using acceleration itself, but the distance is moved? For example; If your acceleration is 1.4G east, your object should go east 14pixels per second until your acceleration changes.

Thus, the movement of the object will look like it is under relative strength, and I think it is more realistic. Fast movement of the device, more effort to create an object.

Also see:

http://www.freescale.com/files/sensors/doc/app_note/AN3397.pdf

and

Using an accelerometer, gyroscope and compass to calculate the movement of a device in the 3D world