Android MotionEvent压力测量单位

Question

I am using the getPressure(index) method from the MotionEvent instance to get a value of the pressure applied to screen.

I am trying to figure out how to convert that value to at least an approximation of a standard measurement unit.

in Android the pressure value is a float ranging from 0 to 1. I need to express it in Newtons in some way. From what i understood this is different across devices so its not possible get a really precise unit measurement but i am fine with an approximation.

Like what amount in newtons is normal for a stylus touching the screen on full force (the device measuring 1.0f of pressure)

Answer 1

I think you can only guess, and know that the results will be affected by huge uncertainity. Solutions I see:

1. Put an object of appropriate, known weight on the screen. Don't know about screens, but if it needs human skin to trigger the event, you can put your finger on the screen (making no strength on it) and then put some object on your finger.

2. Take a stylus, and by debugging learn how much force you need to get a 0.5f result. Then take a scale (foreign speaker here; I mean the tool that measures weights..?) and apply the same pressure on it with the stylus, and read the results.

In both cases, you can have a single map point (eg, 0.5f -> 10 N ), and then assume a linear dependency (knowing also that 0f -> 0 N ) to fill the whole range.

With some patience you can fill different values too - I would not expect the relation to be linear actually.

Answer 2

getPressure returns a value 0-1 because the way pressure is calculated is device-dependant. Some devices will calculate the value from how much of the area of your finger is touching the screen. So from that it's probably not possible to convert to newtons in a way which will work on multiple Android devices unless you write a solution for each one.