R/planar2lonlat.r

In jae0/emgis: Package that interacts with stmv.

  planar2lonlat = function (x, proj.type, planar.coord.scale=NULL, newnames = c("lon", "lat")  ) {
    #// inverse projection: planar to lon/lat using proj
    #// convert planar coord systems (length scale defined in the CRS as +units=km or m)  to lon-lat
   
     ## use of this is deprecated
    if ( !is.null( planar.coord.scale)) {
      # planar.coord.scale is the multiplier applied upon the planar coords
      # when planar.coord.scale=1000 .. it is converting incoming data (km) to m ## deprecated use +units=km
      # when planar.coord.scale=1 .. it means no conversion as it is already in m ## deprecated use +units=m
      stop( "Use of planar.coord.scale is deprecated, use +units=km (default) in proj4 CRS")
      #x$plon = x$plon * planar.coord.scale
      #x$plat = x$plat * planar.coord.scale  
    }

  # first try an internal conversion /lookup for CRS  
    proj4.params = NULL
    pcrs = lookup.projection.params(proj.type)
    if (!is.null(pcrs)) proj4.params = try( sp::CRS( pcrs ), silent=TRUE )

    # if internal lookup does not work then try to directly pass to CRS   
    if ( is.null(proj4.params) | inherits(proj4.params, "try-error")) {
      if (!is.null(proj.type))  proj4.params = try( sp::CRS( proj.type ), silent=TRUE )
    }
    if ( inherits(proj4.params, "try-error") ) {
      print( proj.type )
      warning( "Projection not recognised") 
    }
    
    crsX = rgdal::CRSargs( proj4.params)
    if ( ! grepl("units", crsX) ) {
      print (crsX)
      stop( "The proj4 CRS requires an explicit +units=km ")
    }
    y = rgdal::project( cbind(x$plon, x$plat), crsX, inv=T ) 
    colnames(y) = newnames  
    for (i in 1:length( newnames)) {
      if ( newnames[i] %in% colnames(x) ) x[, newnames[i]] = NULL   
    }
    x = cbind(x,y)
    return (x)
  }