plot - Plotting netcdf in R with correct grid -

my goal plot nitrate (no3) data on world map, using correct longitude , latitude these data.

there 2 netcdf files:
1. with data
2. with grid information

summary info on data: no3 array of length x*y*sigma no3_df 'x*y obs. of 3 variables' x = integer [180] y = integer [193] sigma = array[53]

i want @ sigma ('depth') 20. therefore did following:

# load needed libraries handle netcdf files library(ncdf) library(akima)  # open data , grid files file1 <- open.ncdf(file.choose()) grid  <- open.ncdf(file.choose())  # read relevant variables/parameters data file1 x <- get.var.ncdf(file1,varid="x") y <- get.var.ncdf(file1,varid="y") sigma <- get.var.ncdf(file1,varid="sigma") no3 <- get.var.ncdf(file1,varid="no3") sigma_plot <- no3[,,sigma=20]  # read relevant variables/parameters grid file plon <- get.var.ncdf(grid,varid="plon") plat <- get.var.ncdf(grid,varid="plat")  # each cell of sigma_plot corresponds 1 cell of plon , plat. <- array(c(plon,plat,sigma_plot),dim=c(180,193,3))  # b array containing each row: (longitude, latitude, value). b <- apply(a, 3, cbind)  # not regular grid, interpolate regular grid. akima library c <- interp(b[,1],b[,2],b[,3],              xo=seq(-180,180,1),yo=seq(-90,90,by=1), # tweak here resolution             duplicate='mean') # y values duplicates  ######### # plotting #########  # 1 works, doesn't have correct longitude , latitude: filled.contour(x,y,sigma_plot, col=rich.colors(18))  # try plot lon , lat filled.contour(c, col=rich.colors(30)) 

since filled.contour plot doesn't have correct longitude , latitude, use ggplot. however, don't know how this...

# , plotting ggplot ggplot(aes(x=plon_datafrm,y=plat_datafrm),data=no3_df) +   geom_raster() +   coord_equal() +   scale_fill_gradient() 

this doesn't seem work. net ggplot might reason, appreciate help.

library(ncdf) data <- open.ncdf(file1) no3 <- get.var.ncdf(data,varid="no3") sigma_plot <- no3[,,20] grid <- open.ncdf(file2) plon <- get.var.ncdf(grid,varid="plon") plat <- get.var.ncdf(grid,varid="plat") 

contrary understood, each cell of sigma_plot corresponds 1 cell of plon , plat.

a <- array(c(plon,plat,a),dim=c(180,193,3)) b <- apply(a, 3, cbind) 

now b array containing each row: (longitude, latitude, value). not regular grid, need interpolate regular grid. easiest way using interp package akima:

library(akima) c <- interp(b[,1],b[,2],b[,3],              xo=seq(-180,180,1),yo=seq(-90,90,by=1), #you can tweak here resolution             duplicate='mean') #for reasons entries duplicates, don t know how want handle it.  image(c) #for instance, or filled.contour if prefer library(maptools) data(wrld_simpl) plot(wrld_simpl, add=true, col="white") #to add simple world map on top