R help - Sep 2009 - Function to find angle between coordinates?

Dear all,

I was doing some self study and was wondering if a function already
exists which allows one to determine the angle between points.  e.g.
given the following (x,y) coordinates

input: (0,1); (0,0); (1,0)

would result in:

output: 90 degrees

Best regards
C.C.

Since the inner product of two vectors if the cos of the
angle between them:
> A <- c(0,1); O <- c(0,0); B <- c(1,0)
> acos((A-O) %*% (B-O)) * 180 / pi
     [,1]
[1,]   90


On Tue, Sep 1, 2009 at 9:08 AM,
clair.crossupton at googlemail.com<clair.crossupton at googlemail.com>
wrote:
> Dear all,
>
> I was doing some self study and was wondering if a function already
> exists which allows one to determine the angle between points. ?e.g.
> given the following (x,y) coordinates
>
> input: (0,1); (0,0); (1,0)
>
> would result in:
>
> output: 90 degrees
>
> Best regards
> C.C.

That is if they have length 1 as is the case here.  Normalize them
to length 1, if not.

On Tue, Sep 1, 2009 at 11:06 AM, Gabor
Grothendieck<ggrothendieck at gmail.com> wrote:
> Since the inner product of two vectors if the cos of the
> angle between them:
>
>> A <- c(0,1); O <- c(0,0); B <- c(1,0)
>> acos((A-O) %*% (B-O)) * 180 / pi
> ? ? [,1]
> [1,] ? 90
>
>
> On Tue, Sep 1, 2009 at 9:08 AM,
> clair.crossupton at googlemail.com<clair.crossupton at
googlemail.com>
> wrote:
>> Dear all,
>>
>> I was doing some self study and was wondering if a function already
>> exists which allows one to determine the angle between points. ?e.g.
>> given the following (x,y) coordinates
>>
>> input: (0,1); (0,0); (1,0)
>>
>> would result in:
>>
>> output: 90 degrees
>>
>> Best regards
>> C.C.
>

?atan2 is a possible starting point. 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of clair.crossupton at googlemail.com
Sent: Tuesday, September 01, 2009 8:09 AM
To: r-help at r-project.org
Subject: [R] Function to find angle between coordinates?

Dear all,

I was doing some self study and was wondering if a function already
exists which allows one to determine the angle between points.  e.g.
given the following (x,y) coordinates

input: (0,1); (0,0); (1,0)

would result in:

output: 90 degrees

Best regards
C.C.

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Thank you very much, these were exactly what i needed!  :-)

C.C.

On 1 Sep, 14:08, "clair.crossup... at googlemail.com"
<clair.crossup... at googlemail.com> wrote:
> Dear all,
>
> I was doing some self study and was wondering if a function already
> exists which allows one to determine the angle between points. ?e.g.
> given the following (x,y) coordinates
>
> input: (0,1); (0,0); (1,0)
>
> would result in:
>
> output: 90 degrees
>
> Best regards
> C.C.
>
> ______________________________________________
> R-h... at r-project.org mailing
listhttps://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.