[R-sig-Geo] Distance calculating between points according to a river network

[Chris Reudenbach]

Tristan,

if I understand you right you just want to calculate the distances. So 
no hydro stuff like accumulation flow directions etc.? As well as no 
diffusion modeling of the pollutants.

Most of the traditional vector based GIS stuff is packed into the rgeos 
package. So you might calculated the distances along a graph like in the 
following paste and copy snippet.

cheers Chris



library(rgeos)
library(sp)
# just for visualisation
r <- raster(nrows=6, ncols=7, xmn=0, xmx=7, ymn=0, ymx=6, crs="+proj=utm 
+units=m")
r[] <- c(1, 0, 1, 0, 1, 0, 1,
          0, 1, 0, 1, 0, 1, 0,
          1, 0, 1, 0, 1, 0, 1,
          0, 1, 0, 1, 0, 1, 0,
          1, 0, 1, 0, 1, 0, 1,
          0, 1, 0, 1, 0, 1, 0)
# river line
line 
<-SpatialLines(list(Lines(Line(cbind(c(5.5,1.5,4.5),c(1.5,5.5,5.5))), 
ID="line")))
# points
p1 <-as.data.frame(cbind(4.5,2.5))
p2 <-as.data.frame(cbind(2.5,4.5))
p3 <-as.data.frame(cbind(2.1,4.5))
p4 <-as.data.frame(cbind(3.5,5.5))
p5 <-as.data.frame(cbind(3.5,5.7))
sp::coordinates(p1) <- ~V1+V2
sp::coordinates(p2) <- ~V1+V2
sp::coordinates(p3) <- ~V1+V2
sp::coordinates(p4) <- ~V1+V2
sp::coordinates(p5) <- ~V1+V2
projection(line)<-projection(point)

plot(r)
plot(line,add=TRUE)
plot(p1,add=TRUE)
plot(p2,add=TRUE)
plot(p3,add=TRUE,col="red")
plot(p4,add=TRUE)
plot(p5,add=TRUE,col="red")

# calculate distance along the line
rgeos::gProject(spgeom = line, sppoint = p1)
rgeos::gProject(spgeom = line, sppoint = p2)
rgeos::gProject(spgeom = line, sppoint = p4)

# note if the point is not near the line it is caluclated orthogonal
rgeos::gProject(spgeom = line, sppoint = p3)
rgeos::gProject(spgeom = line, sppoint = p5)



On 25.01.2017 17:31, Romine, Jason wrote:
> The gdistance package in R is what you are looking for:
>
> https://cran.r-project.org/web/packages/gdistance/gdistance.pdf
>
> https://cran.r-project.org/web/packages/gdistance/vignettes/gdistance1.pdf
>
> Best,
> Jason
>
> On Wed, Jan 25, 2017 at 5:22 AM, Tristan Bourgeois <
> tristan.bourgeois at gmail.com> wrote:
>
>> Hi Mirza,
>>
>> Thanks for your quick answer.
>>
>> Actually I don't want to calculate distance between a point and the next
>> downstream one.
>> For example, if there are 4 sewage plant on a river and 7 measurment
>> stations,I want the distance between each sewage plant and each station.
>> (water pollution dispersion calculation).
>> So the flow direction is not that important in my case. The difficulty is
>> to get the distance between a point and another one following the river
>> polyline.
>>
>> In your case, you can add a raster layer with elevation values ans extract
>> the elevation  for each point of your layer.  Then, for each polyline it is
>> possible to define a flow direction.
>> Hope it will help you.
>>
>>
>>
>>
>> 2017-01-25 11:57 GMT+01:00 Mirza Cengic <mirzaceng at gmail.com>:
>>
>>> Hi Tristan,
>>>
>>> I recently had to do something similar (calculating distance to the next
>>> downstream point), and I was not able to find a solution with R that
>> would
>>> deal with the direction of the flow. Perhaps someone who has deeper
>>> understanding of packages such as iGraph etc. might be able to find a
>>> solution, but I wasn't.
>>> I solved the problem with ArcMap, using HydroTools extension, where you
>>> need to define a geometric network that has a direction, and then the
>>> calculation is pretty straightforward with HydroTools (let me know if you
>>> need more info).
>>> I would prefer to have a scripted solution in an open-source software,
>> but
>>> this worked for me in any case. If anyone has a better way for solving
>>> this, I would love to see how!
>>>
>>> Cheers,
>>> Mirza.
>>>
>>
>>
>> --
>> Tristan Bourgeois
>>
>>          [[alternative HTML version deleted]]
>>
>> _______________________________________________
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>> R-sig-Geo at r-project.org
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>>
>>
>

-- 
Dr Christoph Reudenbach, Philipps-University of Marburg, Faculty of Geography, GIS and Environmental Modeling, Deutschhausstr. 10, D-35032 Marburg, fon: ++49.(0)6421.2824296, fax: ++49.(0)6421.2828950, web: gis-ma.org, giswerk.org, moc.environmentalinformatics-marburg.de