[R-sig-Geo] Raster stream network to lines

[Michael Sumner]

Not much to add but if you didn't notice there is a degenerate line in that
isolated pixel, so if you were looking at sets of connected pixels in turn
you could possibly re-process the output of contourLines to join things up:

cl <- contourLines(list(x = xFromCol(foo), y  = rev(yFromRow(foo)), z =
as.matrix(t(flip(foo, "y")))), levels = 1)

## the third one is a nearly-degenerate line in the centre of the isolated
cell
cl[[3]]

Cheers, Mike.

On Thu, 19 Apr 2018 at 08:22 Andy Bunn <Andy.Bunn at wwu.edu> wrote:

> Brilliant! And a heck of a workaround. But what if foo is a projected
> raster? I can add a projection system but all the coordinate info is lost
> in the shuffle.
>
> On 4/18/18, 1:17 PM, "Joseph Stachelek" <joseph.stachelek at gmail.com>
> wrote:
>
>     Hi Andy,
>
>     I have posted some code showing one way of doing this
>     with the `sf` package:
>
>     https://gist.github.com/jsta/d8d8e8d79877c720b6842ae8efa2
>     b9b8
>
>     If you are doing this a lot I recommend picking up GRASS:
>
>     https://grasswiki.osgeo.org/wiki/R.stream.*_modules
>     https://grass.osgeo.org/grass74/manuals/r.to.vect.html
>
>     --Joe
>
>     -----Original Message-----
>     From: Andy Bunn <Andy.Bunn at wwu.edu>
>     To: R-sig-Geo <r-sig-geo at r-project.org>
>     Subject: [R-sig-Geo] Raster stream network to lines
>     Date: Wed, 18 Apr 2018 19:03:21 +0000
>
>     I have a raster of streams with 0 being non-stream and 1
>     being stream. Is there a way to convert this into a
>     SpatialLinesDataFrame? rasterToContour() almost does what
>     I want but fails to draw the line on queens rules, etc.
>     Example here:
>
>     library(raster)
>     foo <- matrix(0,ncol=9,nrow=9)
>     foo[1:4,3] <- 1
>     foo[5,4] <- 1
>     foo[6:9,5] <- 1
>     foo <- raster(foo)
>     plot(foo)
>     bar <- rasterToContour(foo,nlevels=1)
>     plot(bar)
>
>     How can I get a continuous line in this example? Many
>     thanks, Andy
>
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>
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-- 
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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