R/LatLon2XY.centered.R

In iNZightVIT/RgoogleMaps: Overlays on Google map tiles in R

`LatLon2XY.centered` <-structure(function#computes the centered coordinate transformation from lat/lon to map tile coordinates 
### The function LatLon2XY.centered(MyMap, lat,lon,zoom) computes the coordinate transformation from lat/lon to map tile coordinates given a map object.
(
  MyMap, ##<< map object 
  lat, ##<< latitude values to transform
  lon, ##<< longitude values to transform
  zoom ##<< optional zoom level. If missing, taken from \code{MyMap}
){
  
  transfXY<-function(MyMap,oldX, oldY)## only use for non proper coordinate transformations
  {
    xlim<-c(MyMap[["BBOX"]][["ll"]][2],MyMap[["BBOX"]][["ur"]][2])
    ylim<-c(MyMap[["BBOX"]][["ll"]][1],MyMap[["BBOX"]][["ur"]][1])
    Rcoords<-list(newX=(oldX-xlim[1])/(xlim[2]-xlim[1]),
                  newY=(oldY-ylim[1])/(ylim[2]-ylim[1]))
    #browser()
    return(Rcoords)
  }
  
  if (MyMap$url == "OSM") {
    return(transfXY(MyMap,lon,lat))
  }
   lat.center <- MyMap[[1]];
   lon.center <- MyMap[[2]];
   if (missing(zoom)) zoom <- MyMap[[3]];
       
   mypoints <- LatLon2XY(lat,lon,zoom);
   mycenter <- LatLon2XY(lat.center,lon.center,zoom);
   
   Rcoords <- Tile2R(mypoints, mycenter);
   
  ##seealso<< \link{LatLon2XY} \link{Tile2R} 
   return(list(newX=Rcoords$X,newY=Rcoords$Y));
### properly scaled and centered (with respect to the center of \code{MyMap} ) coordinates  
###  \item{newX }{ transformed longitude}
###  \item{newY }{transformed latitude}
})