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~/ ANGLEIJK.MAC (1.1):  expression to calculate the turning angle of a turn
~/                
~/ The result of this expression is the turning angle in degrees, ranging
~/ from -180 to +180.  A zero angle corresponds to a straight through turn,
~/ negative values imply left turns and positive values imply right turns.
~/
~/ Note that the expression will cause division by zero for u-turns. But
~/ these are benign and still lead to the numerically correct result -180.
~/
~/ 94-09-28 Heinz Spiess, EMME/2 Support Center, CH-2558 Aegerten, Switzerland
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180.*atan(put((xk-xj)*(yj-yi)-(yk-yj)*(xj-xi))/
put((xk-xj)*(xj-xi)+(yk-yj)*(yj-yi)))/3.1415926
+360*((get(1)>0)-.5)*(get(2)<0)