latlong2grid {SpatialEpi}

Convert Coordinates from Latitude/Longitude to Grid

Description

Convert geographic latitude/longitude coordinates to kilometer-based grid coordinates.

Usage

latlong2grid(input)

Arguments

input

either an ⁠n x 2⁠ matrix of longitude and latitude coordinates in decimal format or an object of class SpatialPolygons

Details

Longitude/latitudes are not a grid-based coordinate system: latitudes are equidistant but the distance between longitudes varies.

Value

Either a data frame with the corresponding (x,y) kilometer-based grid coordinates, or a SpatialPolygons object with the coordinates changed.

Note

Rough conversion of US lat/long to km (used by GeoBUGS): (see also forum.swarthmore.edu/dr.math/problems/longandlat.html). Radius of earth: r = 3963.34 (equatorial) or 3949.99 (polar) mi = 6378.2 or 6356.7 km, which implies: km per mile = 1.609299 or 1.609295 a change of 1 degree of latitude corresponds to the same number of km, regardless of longitude. arclength=r*theta, so the multiplier for coord y should probably be just the radius of earth. On the other hand, a change of 1 degree in longitude corresponds to a different distance, depending on latitude. (at N pole, the change is essentially 0. at the equator, use equatorial radius.

Author(s)

Lance A. Waller

Examples

## Convert coordinates
coord <- data.frame(rbind(
 # Montreal, QC:  Latitude: 45deg 28' 0" N (deg min sec), Longitude: 73deg 45' 0" W
 c(-73.7500, 45.4667),
 # Vancouver, BC:  Latitude: 45deg 39' 38" N (deg min sec), Longitude: 122deg 36' 15" W
 c(-122.6042, 45.6605)
))
latlong2grid(coord)
## Convert SpatialPolygon
data(pennLC)
new <- latlong2grid(pennLC$spatial.polygon)
par(mfrow=c(1,2))
plot(pennLC$spatial.polygon,axes=TRUE)
title("Lat/Long")
plot(new,axes=TRUE)
title("Grid (in km)")