I must confess I just took took the difference between the first and last Cartesian co-ordinates and multiplied it by the inverse of the distance? as below? I just assumed it would do? 

$Xl1 = -3.901
$Yl1 = 9.352
$Zl1 = -1.557

$Xl2 = -47.430
$Yl2 = -2.993
$Zl2 = -17.639

$Axx = $Xl1 - $Xl2; 
$Axy = $Yl1 - $Yl2;
$Axz = $Zl1 - $Zl2;

$Vform = V($Axx,$Axy,$Axz);

$vector = sqrt($Axx**2 + $Axy**2 + $Axz**2);

$Unitvector = 1/$vector * $Vform;

[download]

best wishes Dan

In reply to Re^12: Polar Co-Ordinates: Rotating a 3D cartesian point around a fixed axis? by fraizerangus
in thread Polar Co-Ordinates: Rotating a 3D cartesian point around a fixed axis? by fraizerangus

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