hi, also, make sure you have set the aspect ratio to 1:1 when plotting (asp=1).
HTH, baptiste On 25 August 2010 10:20, Benno Pütz <pu...@mpipsykl.mpg.de> wrote: > 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. >> >> >> >> -- >> View this message in context: >> http://r.789695.n4.nabble.com/Draw-a-perpendicular-line-tp2335882p2335882.html >> Sent from the R help mailing list archive at Nabble.com. >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- ____________________ Dr. Baptiste Auguié Departamento de Química Física, Universidade de Vigo, Campus Universitario, 36310, Vigo, Spain tel: +34 9868 18617 http://webs.uvigo.es/coloides ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.