R help - Jan 2004 - arrows on contour lines

Hello everybody

I'm using contour() to draw streamlines of potential flow, eg

  jj <- seq(from= -4, to=4,len=20)
  jj <- outer(jj,jj,function(x,y){x})+1i*outer(jj,jj,function(x,y){y})

  f <- function(x){x^2}
  contour(Im(f(jj)), nlevels=44 , labels="")

How best to put arrows on the contour lines to show the direction of flow?
  (ie  I want contour lines looking like ---<---  and ---->----)

I think this is a lot of work, which I don't mind doing, but it'd be 
good to hear the list's ideas before starting to bark up the wrong 
tree, so to speak.



-- 
Robin Hankin
Uncertainty Analyst
Southampton Oceanography Centre
SO14 3ZH
tel +44(0)23-8059-7743
initialDOTsurname at soc.soton.ac.uk (edit in obvious way; spam precaution)

Hi

On 14 Jan 2004 at 12:01, Robin Hankin wrote:
> Hello everybody
> 
> I'm using contour() to draw streamlines of potential flow, eg
> 
>   jj <- seq(from= -4, to=4,len=20)
>   jj <- outer(jj,jj,function(x,y){x})+1i*outer(jj,jj,function(x,y){y})
> 
>   f <- function(x){x^2}
>   contour(Im(f(jj)), nlevels=44 , labels="")
something like that 

contour(Im(f(jj)), nlevels=44 , labels=c(">","<"))

will give you direction.

I would use some coded vector of directions for selecting a direction
> vec<-rep(c(1,2),22)
> set.seed(1)
> vec<-sample(vec,44)
>   contour(Im(f(jj)), nlevels=44 ,
labels=c(">","<")[vec])
will give you directions.

Hope this helps

Petr
> 
> How best to put arrows on the contour lines to show the direction of
> flow?
>   (ie  I want contour lines looking like ---<---  and ---->----)
> 
> I think this is a lot of work, which I don't mind doing, but it'd
be
> good to hear the list's ideas before starting to bark up the wrong
> tree, so to speak.
> 
> 
> 
> -- 
> Robin Hankin
> Uncertainty Analyst
> Southampton Oceanography Centre
> SO14 3ZH
> tel +44(0)23-8059-7743
> initialDOTsurname at soc.soton.ac.uk (edit in obvious way; spam
> precaution)
> 
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Petr Pikal
petr.pikal at precheza.cz