Create grid with equal spacings R from specific latitude and longitude

Question

I would like to create a grid of 4 points with lat lons (1 x 4) each 150m apart using a specific point as the start, e.g., top left of the grid. My starting point is Latitude 51.83985301, Longitude 0.885039037 would be Point 1. Can I do this in R?

Point 1 (x,y)    Point 2 (x,y)
Point 3 (x,y)    Point 4 (x,y)

Answer 1

Yes--You can do this in R!

# Use this R package
require( geosphere )

# Example distance and point
distance <- 150
tplon    <- 0.885039037
tplat    <- 51.83985301

ELLIPSOID <- tibble::tribble(
  # Data are from help( 'distVincentyEllipsoid' ) 
   ~name              ,   ~a        ,      ~b       ,     ~f
 , 'WGS84'              , 6378137     , 6356752.3142  , 1/298.257223563
 , 'GRS80'              , 6378137     , 6356752.3141  , 1/298.257222101
 , 'GRS67'              , 6378160     , 6356774.719   , 1/298.25
 , 'Airy 1830'          , 6377563.396 , 6356256.909   , 1/299.3249646
 , 'Bessel 1841'        , 6377397.155 , 6356078.965   , 1/299.1528434
 , 'Clarke 1880'        , 6378249.145 , 6356514.86955 , 1/293.465
 , 'Clarke 1866'        , 6378206.4   , 6356583.8     , 1/294.9786982
 , 'International 1924' , 6378388     , 6356911.946   , 1/297
 , 'Krasovsky 1940'     , 6378245     , 6356863       , 1/298.2997381
)

# Choose an ellipsoid to use
cfg      <- ELLIPSOID[ ELLIPSOID$name == 'WGS84', ]

# A function to determine the next point, given
# the current point, direction, and distance

from_here_this_way_so_far <- function( lon, lat, direction, distance = 150 ){
  geodesic(
        p = cbind( lon, lat )
    , azi = direction
    ,   d = distance
    ,   a = cfg$a
    ,   f = cfg$f
  )[ 1:2 ]
}

# Demonstrate on the example
from_here_this_way_so_far( tplon, tplat, 0.00, 150 )
## [1]  0.885 51.841

# Get bearings for east, west, north, and south
bear <- list(
    # Positive longitude change
    east = bearing( c( tplon, tplat ), c( tplon+0.001, tplat ) )
    # Negative longitude change
  , west = bearing( c( tplon, tplat ), c( tplon-0.001, tplat ) )
    # Positive latitude change
  , north = bearing( c( tplon, tplat ), c( tplon, tplat+0.001 ) )
    # Negative latitude change
  , south = bearing( c( tplon, tplat ), c( tplon, tplat-0.001 ) )
)

# A function to determine the coordinates for each corner of the square
corners <- function( lon, lat ){
  A <- c( lon, lat )
  B <- from_here_this_way_so_far( lon, lat, bear$east, 150 )
  C <- from_here_this_way_so_far( B[1], B[2], bear$south, 150 )
  D <- from_here_this_way_so_far( lon, lat, bear$south, 150 )

  ## E <- from_here_this_way_so_far( C[1], C[2], bear$west, 150 )
  ## all.equal( D, E )
  ## [1] TRUE

  result = cbind( A, B, C, D )
  row.names( result ) <-  c('lon','lat')
  result
}

# Demonstrate using the example
corners( tplon, tplat )
##        A       B       C      D
## lon  0.885  0.8872  0.8872  0.885
## lat 51.840 51.8399 51.8385 51.839