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

[Andy Bunn]

While Joe’s solution worked great (except the projection info) I know when I’m beat. I used the channel network tool in QGIS.

From: Michael Sumner <mdsumner at gmail.com>
Date: Wednesday, April 18, 2018 at 8:30 PM
To: Andy Bunn <Andy.Bunn at wwu.edu>
Cc: Joseph Stachelek <joseph.stachelek at gmail.com>, R-sig-Geo <r-sig-geo at r-project.org>
Subject: Re: [R-sig-Geo] Raster stream network to lines

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<mailto: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<mailto: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<mailto:Andy.Bunn at wwu.edu>>
    To: R-sig-Geo <r-sig-geo at r-project.org<mailto: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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Dr. Michael Sumner
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