Modifying contours

Hi all,

I am trying to do the following to produce a customized contour plot:

1. Create a ContourSet from contour()
2. Retrieve vertex positions from this ContourSet
3. Modify the vertex positions by applying a coordinate transformation
4. Apply the changes to the ContourSet
5. Plot the ContourSet

At the moment, I do:

c = contour(image)

then I can get the vertex positions with

for collection in contours.collections:
  for polygon in collection.get_paths():
    x = polygon.vertices[:,0]
    y = polygon.vertices[:,1]

Then, I can apply mathematical operations to x and y, and replace c.collections with a new set of LineCollections. So c now contains an updated collections set.

My question is, how do I now plot these modified contours? I intuitively tried show(c) and draw(c), but now luck. Since I am a beginner at python, this may actually be obvious, but I can't figure it out!

I also have a minor problem with:

c = contour(image)

as this will draw the contours straight away onto the image, but I don't want this to be the case, as I only want to show the modified contours. I am using 'ipython -pylab' to run python, so I am guessing that this is something to do with the fact that ipython refreshes the plot at each plotting command? Is there an easy fix to prevent that in this case?

Thank you for any help!