# latlong2grid: Convert Coordinates from Latitude/Longitude to Grid In SpatialEpi: Methods and Data for Spatial Epidemiology

## Description

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

## Usage

 `1` ```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.

Lance A. Waller

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16``` ```## 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)") ```

SpatialEpi documentation built on Aug. 2, 2021, 9:07 a.m.