# lonlat2xy: Projects lon/lat coordinates to x/y Euclidean coordinate... In spectralGP: Approximate Gaussian Processes Using the Fourier Basis

## Description

The projection calculates, for all points, the great circle distance in the x direction to the mean longitude and in the y direction to the mean latitude, and uses these distances as the x-y coordinates of the location. This function is copied from the fields library.

## Usage

 `1` ```lonlat2xy(lnlt,miles=FALSE) ```

## Arguments

 `lnlt` A two-column matrix-like object of lon/lat coordinates to be projected, with longitude in the first column. `miles` Indicator of whether distances should be calculated in miles or kilometers (FALSE, the default).

## Details

Note that this is an ad hoc projection best used only for small portions of the globe.

## Value

A two-column matrix of projected x/y coordinates, with the x-coordinate in the first column.

## Author(s)

copied from the fields library by Christopher Paciorek [email protected]

`xy2unit`, `new.mapping`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17``` ```library(spectralGP) gp1=gp(c(128,128),matern.specdens,c(1,4)) n=100 locs=cbind(runif(n,20,80),runif(n,40,50)) locs.predict=cbind(runif(n,30,90),runif(n,38,48)) locs=lonlat2xy(locs) locs.predict=lonlat2xy(locs.predict) scaled.locs=xy2unit(locs,rbind(locs,locs.predict)) scaled.locs.predict=xy2unit(locs.predict,rbind(locs,locs.predict)) train.map=new.mapping(gp1,scaled.locs) predict.map=new.mapping(gp1,scaled.locs.predict) plot(locs,xlim=c(min(locs[,1],locs.predict[,1]),max(locs[,1], locs.predict[,1])),ylim=c(min(locs[,2],locs.predict[,2]), max(locs[,2],locs.predict[,2]))) points(locs.predict,col=2) plot(scaled.locs,xlim=c(0,1),ylim=c(0,1)) points(scaled.locs.predict,col=2) ```