iBeacon detections not giving accurate location for the indoor navigation

Question

I am looking into the possibility to use multiple iBeacons for indoor position location. i have tried the trilateration formula. but i think there is some problem its not giving the adjust location.

I have three iBeacons at a specific position

CGPoint a=CGPointMake(100, 0);
CGPoint b=CGPointMake(160, 270);
CGPoint c=CGPointMake(0, 145);

On didRangeBeacons i am getting the following distance

    float ra =0.0f;
    float rb=0.0f ;
    float rc=0.0f ;

     for (CLBeacon *beacon in beacons) {
        if ([beacon.minor floatValue]==57726) {
            //ra = beacon.accuracy; ra=5.33124
            ra = beacon.proximity;
        }
        if ([beacon.minor floatValue]==31901) {
            //  rb = beacon.accuracy;  rb=0.185142
            rb = beacon.proximity;
        }
        if ([beacon.minor floatValue]==53482) {
            // rc = beacon.accuracy;  rc=3.23776
            rc = beacon.proximity;
        }
    }

At the end i am using the trilateration formula.

float S = (pow(c.x, 2.) - pow(b.x, 2.) + pow(c.y, 2.) - pow(b.y, 2.) + pow(rb, 2.) - pow(rc, 2.)) / 2.0;

    float T = (pow(a.x, 2.) - pow(b.x, 2.) + pow(a.y, 2.) - pow(b.y, 2.) + pow(rb, 2.) - pow(ra, 2.)) / 2.0;
    float y = ((T * (b.x - c.x)) - (S * (b.x - a.x))) / (((a.y - b.y) * (b.x - c.x)) - ((c.y - b.y) * (b.x - a.x)));
    float x = ((y * (a.y - b.y)) - T) / (b.x - a.x);

OutPut of the location

point = (x=138.025452, y=133.269165)

But its not a perfect. it should give the point near to the Point b. i dnt have an idea whats the wrong.

Please help.

Paulw11 Paulw11 · Accepted Answer · 2014-06-10T10:19:48

I am not sure that you are going to be able to get a very accurate position. The Apple documentation for the CLBeacon accuracy property states -

Discussion Indicates the one sigma horizontal accuracy in meters. Use this property to differentiate between beacons with the same proximity value. Do not use it to identify a precise location for the beacon. Accuracy values may fluctuate due to RF interference.

As it is a one sigma accuracy, it is only about 68% accurate.

It is possible that you may get better results if you calibrate your beacons, but even then RF interference from the environment (people in particular) will affect your readings

iBeacon detections not giving accurate location for the indoor navigation

1 Answers