Topographic distance

Calculates topographic corrected distance for a SpatialLinesDataFrame object

topo.distance(x, r, echo = FALSE)

Arguments

x	sp SpatialLinesDataFrame object
r	raster class elevation raster
echo	(FALSE/TRUE) print progress to screen

Value

Vector of corrected topographic distances same length as nrow(x)

Note

This function corrects straight-line (euclidean) distances for topographic-slope effect.

Author

Jeffrey S. Evans <jeffrey_evans@tnc.org>

Examples

# \donttest{     
 library(sp)
 library(raster)
 library(GeNetIt)
 
 # create example data
 data(elev)
   r <- projectRaster(elev, res=c(1000,1000), 
                      crs="+proj=aea +lat_1=29.5 +lat_2=42.5")
#> Warning: CRS object has no comment
#> Warning: CRS object has no comment
#> Warning: Using PROJ not WKT2 strings
#> Warning: Using PROJ not WKT2 strings
   e <- extent(616893.6,714697.3,5001027,5080542)
     elev <- crop(r,e) 
#> Error in .local(x, y, ...): extents do not overlap
       names(elev) <- "elev"
 pts <- sampleRandom(elev, 10, sp=TRUE)
   pts$ID <- LETTERS[seq( from = 1, to = nrow(pts) )]
   
 graph <- GeNetIt::knn.graph(pts, row.names=pts@data[,"ID"])
   proj4string(graph) <- proj4string(elev)
#> Warning: CRS object has comment, which is lost in output
   head(graph@data)
#>   i j from_ID to_ID   length
#> 1 1 2       A     B 1.500000
#> 2 1 3       A     C 1.414214
#> 3 1 4       A     D 0.500000
#> 4 1 5       A     E 0.500000
#> 5 1 6       A     F 1.802776
#> 6 1 7       A     G 1.414214
  
 plot(elev)
   plot(graph, cex=0.5, add=TRUE)
   plot(pts,pch=19,col="red",add=TRUE)
 
 # Calculate topographical distance  
 ( tdist <- topo.distance(graph, elev) )
#> Warning: working under the assumption of projected data!
#> Warning: Spatial object 1 is not projected; GEOS expects planar coordinates
#> Warning: Spatial object 2 is not projected; GEOS expects planar coordinates
#> Warning: Spatial object 1 is not projected; GEOS expects planar coordinates
#> Warning: Spatial object 2 is not projected; GEOS expects planar coordinates
#> Warning: working under the assumption of projected data!
#> Warning: Spatial object 1 is not projected; GEOS expects planar coordinates
#> Warning: Spatial object 2 is not projected; GEOS expects planar coordinates
#> Warning: Spatial object 1 is not projected; GEOS expects planar coordinates
#> Warning: Spatial object 2 is not projected; GEOS expects planar coordinates
#> Warning: working under the assumption of projected data!
#> Warning: Spatial object 1 is not projected; GEOS expects planar coordinates
#> Error in x@coords[i, , drop = FALSE]: subscript out of bounds
 
 # Increase in corrected distance
 tdist - graph$length
#> Error in eval(expr, envir, enclos): object 'tdist' not found
 
 # Percent increase in corrected distance
 ((tdist - graph$length) / graph$length) * 100
#> Error in eval(expr, envir, enclos): object 'tdist' not found

# }