Convert XY Coordinates to River Locations

This function determines the closest vertex in the river network to each point of XY data and returns a list of river locations, defined as segment numbers and vertex numbers.

xy2segvert(x, y, rivers)

Arguments

x	A vector of x-coordinates to transform
y	A vector of y-coordinates to transform
rivers	The river network object to use

Value

A data frame of river locations, with segment numbers in $seg, vertex numbers in $vert, and the snapping distance for each point in $snapdist.

Note

Conversion to river locations is only valid if the input XY coordinates and river network are in the same projected coordinate system. Point data in geographic coordinates can be projected using project in package 'rgdal', and an example is shown below.

Examples

data(Gulk,fakefish)
head(fakefish)
#>          x       y seg vert fish.id flight flight.date
#> 1 885976.9 6951164   1  595       8      1  2015-04-01
#> 2 891727.6 6943194   1  399      10      1  2015-04-01
#> 3 893895.8 6940549   1  352      14      1  2015-04-01
#> 4 893894.9 6929195   1  116       7      1  2015-04-01
#> 5 878936.0 6959825   1  806      11      1  2015-04-01
#> 6 889340.7 6948910   1  505       9      1  2015-04-01

fakefish.riv <- xy2segvert(x=fakefish$x, y=fakefish$y, rivers=Gulk)
head(fakefish.riv)
#>   seg vert  snapdist
#> 1   1  595 329.34419
#> 2   1  399  40.27721
#> 3   1  352 402.52259
#> 4   1  116 525.06623
#> 5   1  806 355.32753
#> 6   1  505  11.34949

plot(x=Gulk, xlim=c(862000,882000), ylim=c(6978000,6993000))
points(fakefish$x, fakefish$y, pch=16, col=2)
riverpoints(seg=fakefish.riv$seg, vert=fakefish.riv$vert, rivers=Gulk, pch=15, col=4)


## converting a matrix of points stored in long-lat to Alaska Albers Equal Area:
data(line98, Kenai1)
head(line98)  # note that coordinates are stored in long-lat, NOT lat-long
#>           [,1]     [,2]
#> [1,] -150.6810 60.60532
#> [2,] -150.6793 60.60723
#> [3,] -150.6792 60.60760
#> [4,] -150.6792 60.60799
#> [5,] -150.6793 60.60838
#> [6,] -150.6794 60.60874

library(rgdal)
#> Loading required package: sp
#> rgdal: version: 1.2-8, (SVN revision 663)
#>  Geospatial Data Abstraction Library extensions to R successfully loaded
#>  Loaded GDAL runtime: GDAL 2.2.1, released 2017/06/23
#>  Path to GDAL shared files: /usr/share/gdal/2.2
#>  Loaded PROJ.4 runtime: Rel. 4.9.2, 08 September 2015, [PJ_VERSION: 492]
#>  Path to PROJ.4 shared files: (autodetected)
#>  Linking to sp version: 1.2-5 
line98albers <- project(line98,proj="+proj=aea +lat_1=55 +lat_2=65 
    +lat_0=50 +lon_0=-154 +x_0=0 +y_0=0 +datum=NAD83 +units=m +no_defs 
    +ellps=GRS80 +towgs84=0,0,0")
head(line98albers)
#>          [,1]    [,2]
#> [1,] 181039.4 1184516
#> [2,] 181122.8 1184734
#> [3,] 181128.7 1184776
#> [4,] 181126.4 1184820
#> [5,] 181119.3 1184863
#> [6,] 181109.3 1184903

zoomtoseg(seg=c(162,19), rivers=Kenai1)
points(line98albers)