Gwennaël, Does the %% operator work for you?
It gives x mod y (or the remainder after dividing x into y...result is guaranteed to be <=0 and >y) E.g. -150 %% 360 # 210 570 %% 360 # 210 https://stat.ethz.ch/R-manual/R-devel/library/base/html/Arithmetic.html -Dan On Thu, Jan 28, 2016 at 10:38 AM, Jeff Newmiller <jdnew...@dcn.davis.ca.us> wrote: > Functions return one value. > > Look at ?atan2 to address ambiguity in identifying angles. > -- > Sent from my phone. Please excuse my brevity. > > On January 28, 2016 9:09:53 AM PST, "Gwennaël Bataille" < > gwennael.batai...@uclouvain.be> wrote: > >Dear all, > >I'd like to calculate the angle from one point (origin) to another > >(target), whatever their coordinates. > >But I encounter some problems (detailed below). The problem could be > >solved if one of you could answer positively to one of the following > >questions: > > > >1) Is there a function in R converting angles in a standardized manner? > > > >(for example, converting -150 or 570 (=210+360) into 210) > > > >2) If not, would you know a function arccos or arcsin returning two > >different angles as an output instead of one? > > > > > > > >Details: > > > >I'd like to calculate the angle from one point (origin) to another > >(target), whatever their coordinates. > >For this, the acos and asin functions work pretty well when the end > >point is located right and above the starting point (first quarter of > >the trigonometric circle), but are problematic otherwise. > > > ># In the following example, the origin is (0,0) and the target > >(0.8660254, 0.5) is located at an angle of 30° : > >acos( (0.8660254 - 0) )*180/pi > >asin( (0.5 - 0) )*180/pi > ># Both acos and asin give the same answer : 30 > > > ># If now, the origin is (0.8660254, 0.5) and the target is (0,0), the > >target is located at an angle of -150° : > >acos( (0 - 0.8660254) )*180/pi > >asin( (0 - 0.5) )*180/pi > ># Here the results are different : 150 and -30 > > > ># In fact, there are two angle solutions giving the same cosinus : 150 > >and -(150) > ># And for sinus as well : -30 and ( 180 - (-30) ) = 210° = -150° > >-acos( (0 - 0.8660254) )*180/pi > >180 - asin( (0 - 0.5) )*180/pi > ># But I cannot test equality between the two : > >-acos( (0 - 0.8660254) )*180/pi == 180 - asin( (0 - 0.5) )*180/pi > ># FALSE, since 210 != -150 (it's only the case when those two are > >angles) > > > > > >Thank you very much in advance for your answers! > > > >Best regards, > > > > > >Gwennaël > > > >-- > >Gwennaël BATAILLE, PhD student - Teaching assistant > > > >Earth and Life Institute > >Université Catholique de Louvain > >1348 Louvain-la-Neuve > >BELGIUM > > > >______________________________________________ > >R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >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. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. -- Dan Dalthorp, PhD USGS Forest and Rangeland Ecosystem Science Center Forest Sciences Lab, Rm 189 3200 SW Jefferson Way Corvallis, OR 97331 ph: 541-750-0953 ddalth...@usgs.gov [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
