[R] Draw a perpendicular line?

[Benno Pütz]

Maybe

perp.slope = -1/slope
abline(cy - cx*perp.slope, perp.slope)

where cx, cy are x- and y-coordinate of C, resp., and slope the slope you calculated for the line through A and B


Am 24.Aug.2010 um 0:04 schrieb CZ:

> 
> Hi,
> 
> I am trying to draw a perpendicular line from a point to two points.
> Mathematically I know how to do it, but to program it, I encounter some
> problem and hope can get help.  Thanks. 
> 
> I have points, A, B and C.  I calculate the slope and intercept for line
> drawn between A and B.
> I am trying to check whether I can draw a perpendicular line from C to line
> AB and get the x,y value for the point D at the intersection. 
> 
> Assume I get the slope of the perpendicular line, I will have my point (D)
> using variable x and y which is potentially on line AB.   My idea was using
> |AC|*|AC| = |AD|*|AD|+ |CD|*|CD|.  I don't know what function I may need to
> call to calculate the values for point D (uniroot?).
> 
> Thank you. 
> 
> 
> 
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