Labelling contour lines

2 messages · Nathaniel Street, Uwe Ligges

Thu, Nov 4, 2004 4:27 AM #

I am using contour to draw contour lines onto a photo (jpeg) of a leaf on 
a white background.

I have two problems:

1) The contour gets plotted at right angles to the jpeg image. I guess 
this is a problem of referencing the start and end points of the image 
matrix but I can't see how to over come this other than loading in a 
second image that has been rotated 90 degrees and plotting the contours on 
the non-rotated one (obviously a bad solution)

2) I want to be able to select a single contour after they have been 
drawn. I know there is contourLines but I can't see how to relate this to 
the contours plotted. In matlab there is a function to label contours so 
that they can be called by their contour label in order to get the 
coordinates of the contour. Can this be done in R.

Sorry if these are easy / stupid questions. I'm new to all this. I have 
searched previos posts but can't find the answers I need and I would 
rather be able to use R than matlab.

Thanks

Nathaniel Street
         University of Southampton
Plants and Environment Lab
     School of Biological Sciences
Basset Crescent East
    Southampton
SO16 7PX
    tel: +44 (0) 23 8059 4387
 fax: +44 (0) 23 8059 4459
      n.r.street at soton.ac.uk
  http://popyomics.biol.soton.ac.uk/~nat
     ICQ: 203465793

Uwe Ligges

Thu, Nov 4, 2004 11:04 AM #

Nathaniel Street wrote:

I guess you either haven't realized the ordering of the y axis or you 
have created the matrix column-wise instead of row-wise (or vice versa).
I can only guess, because there is no reproducible example...


 > I guess

Not really, what you can to is (extended from ?contour):


  x <- -6:16
  contour(outer(x, x), method = "edge", vfont = c("sans serif", "plain"))
  cL <- contourLines(outer(x, x), levels=75)
  lines(cL[[1]], col="red")

Now you have the contour lines coordinates for level 75 in cL, an 
plotted it afterwards.

Uwe Ligges