# Acceleration minus acceleration from rotation

Richmond richmondmathewson at gmail.com
Wed Feb 11 12:59:21 EST 2015

```On 11/02/15 19:35, Steven Chalmers, UI Insight, Inc. wrote:
> I have played with, and understand, accelerationChanged and
> rotationRateChanged but I have a complex requirement to remove the effect
> of rotation from acceleration.
>
> Imagine a phone lying on its back on the table.
>
> 1)  I want the acceleration numbers generated from tapping the phone on its
> side which causes the phone to slide on the table, which is, of course, the
> easy part.
>
> 2)  I want to eliminate the acceleration values generated from a rotation.
> With the phone lying on its back on the table lifting one side, pivoting on
> the opposite side of the phone on the table, will trigger both
> rotationRateChanged and accelerationChanged.  accelerationChanged is
> triggered because the center of the phone is effectively moving both
> parallel to the table top and perpendicular to the table top as the phone
> is rotated.  These are the acceleration effects I want to eliminate from
> accelerationChanged.
>
> 3)  To put it another way, if you slide the phone along the table while
> also tilting it up on one side, or one end, or both, I only want the
> accelerationChanged values for the slide and not for the tilt.
>
> This is a complex math problem which is beyond my math skills.  I don't
> expect anyone to offer this solution for free and as such I would be happy
> to compensate for a solution.
>
>
> Steven Chalmers
> UI Insight, Inc.
> _______________________________________________
>

I must be really stupid, but this message strikes me as a socking great
leg-pull.

So, here I am with my imaginary phone [ well a pink YEZZ phone if you
want the truth ] lying on the
kitchen table.

My ever so slightly evil black and ginger cat flips the phone across the
table.

My phone does NOT react, NOR has any way of detecting the fact it has
been moved.

Now, let's step back a mo' and have a look at my iPad 1 [second hand,
pitched at me by my second son who is so
hi-tech it keeps me awake at night shaking . . . LOL] . . . now it can
detect when I rotate it, so my desktop goes
from portrait-to-landscape-to-portrait-to-landscape: wow, I can do that
all afternoon; almost as orga***c as sitting
in a launderette watching the laundry going round . . . but, I digress.

What my iPad CANNOT do, is detect if it is moved across a surface, for
the very SIMPLE reason that it doesn't have
"little wheels" or other motion sensors on its underside [ err . . .
backside?].

Now if I lift one side of my iPad and lift it up, so that the other side
remains in contact with the table,
the thing doesn't "see" that either.

So . . . . . ???

Richmond.

```