Labelling contour lines
Nathaniel Street wrote:
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 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
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.
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
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