[R-sig-Geo] Mapping contours from jpg map
b.rowlingson at lancaster.ac.uk
Thu Jul 7 18:56:04 CEST 2011
On Thu, Jul 7, 2011 at 5:25 PM, Sarah Papworth
<sarah.papworth06 at imperial.ac.uk> wrote:
> Dear all,
> I have a jpg map of altitudinal contours in my study area which I
> would like to map and use in R to calculate the altitude and slope of
> GPS coordinates.
> So far, I have painstakingly traced these contours in ArcMap to create
> a shapefile (of polylines) with altitude. I have now imported this
> file shapefile into R.
> What I would like to do is turn it into a raster of slope and
> altitude, but I can't seem to find any method of doing this in the
> online R help archives. Does anyone have any idea which package I
> should be using, or perhaps if it is even possible to turn this type
> of shapefile into a raster?
There's definitely tools for doing this in GRASS-GIS:
but not sure about R. One approach might be:
load shapefile into R as a SpatialLinesDataFrame, so that each line
has its height attribute.
consider a grid of points over the space, and use rgeos functions to
find the nearest contour line and its height. Assign height to that
That will give you a grid that will look a bit like terraces between
the contours, which you could possibly then smooth, although there may
be systematic errors with this method...
I suspect there's a better way by looking at more than one nearby
contour line and doing some interpolation....
Actually the GRASS algorithms are discussed here:
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