Identify a linear feature on a raster map and return a linear shape object using R

Question

I would like to identify linear features, such as roads and rivers, on raster maps and convert them to a linear spatial object (SpatialLines class) using R.

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Answer 1

You can get the boundary of that polygon as SpatialLines by direct coercion:

rLines <- as(rPoly, "SpatialLinesDataFrame")

Summarizing the coordinates down to a single "centre line" would be possible, but nothing immediate that I know of. I think that process is generally called "skeletonization":

http://en.wikipedia.org/wiki/Topological_skeleton