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Speed and Heading calculation starting from GPS coordinate

Thu, 12/10/2009 - 07:34 am

Simple tool for the calculation of Speed and heading starting from Latitude and Longitude.

//Thanks to darcas.net/index.php/2008/10/12/calcolo-della-distanza-tra-due-punti-geografici/

Function SpeedAndHeading(TimeWv, LatWv, LonWv) 

Wave TimeWv, LatWv, LonWv

Duplicate/O TimeWv, Speed_Knot

Duplicate/O TimeWv, Speed_m_s

Duplicate/O TimeWv, Heading

Variable i,  z1, z2, HeadTmp

For(i=0;i<=NumPnts(TimeWv);i+=1)

    //Speed Calculation

    Speed_m_s[i] = (1000 * ( ACOS(SIN(Rad(latWv[i]))*SIN(Rad(latWv[i+1]))+COS(Rad(latWv[i]))*COS(Rad(latWv[i+1]))*COS(Rad(lonWv[i+1])-Rad(lonWv[i])))*6372.795477598))/(timeWv[i+1]-TimeWv[i])      

    Speed_Knot[i] = Speed_m_s[i] / 0.514444

    //heading Calculation

    Z1 = SIN(Rad(lonWv[i+1]) - Rad(lonWv[i])) * cos(Rad(latWv[i+1]))    

    Z2 = Cos(Rad(LatWv[i])) * Sin(Rad(LatWv[i+1])) - Sin(Rad(LatWv[i])) * Cos(Rad(LatWv[i+1])) * Cos(Rad(LonWv[i+1]) - Rad(LonWv[i]))   

    HeadTmp = (Grad( Atan2(Z1, Z2)))

    Heading[i] = (HeadTmp < 0) ? HeadTmp+360 : HeadTmp

EndFor

End

Function Rad(Gr)

Variable Gr

Return (PI * Gr /180)

End

Function Grad(Rad)

Variable Rad

Return (180 * Rad / Pi)

End