# How to calculate the direction of movement

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Created: Den123
(11 May 2008)

Last edited: hamishwillee
(26 Jul 2012)

To calculate the direction of movement enough to know coordinates of two consistently received landmarks.

If you use the Cartesian coordinate system and adopt the longitude on the axis "X", latitude on the axis "Y" - then it is possible to calculate the vector of movement.

The following image demonstrates how to calculate vector of the movement and the angle of the vector:

Depending on the direction, you must perform correction of meaning angle.

The following code snippet demonstrates how to calculate the angle of the movements (relative to north), knowing consistently received two landmarks.

TReal alpha; // result

// calculate vector coordinates

TReal y = LatitudeB - LatitudeA,

x = LongitudeB - LongitudeA;

// hypotenuse

TReal sqrtResult = 0;

Math :: Sqrt( sqrtResult, x * x + y * y );

TReal angle;

Math :: ASin( angle, Abs( x ) / sqrtResult );

alpha = angle * 180 / KPi; // angle from North in degrees

// correction

if( x > 0 )

{

// I or IV quadrant

if( y < 0 )

{

// IV quadrant

alpha = 180 - alpha;

}

}

else

{

// II or III quadrant

if( y > 0 )

{

// II quadrant

alpha = -alpha;

}

else

alpha = alpha - 180;

}

How about arctan(x/y) ?