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I have around 100 stations of data spread over around 60 deg lon x 50 deg lon which I want to save as a netcdf using R. Do I have to make a netcdf with all grid points with non-stations being NAN or can I just store the stations (with positions) as netcdf and plot lon/lat wise when needed on a map? I need to make a NETCDF so that I can plot this dataset using other software like GRADS or compare with topography etc.

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  • Why do you want to save it as a netcdf? If it is just station data (x,y,m) then another file format might be better. – Spacedman Aug 21 '17 at 10:44
  • netcdf so that I can plot using other plotters such as grads if required. – Trina Aug 21 '17 at 11:05
  • if you want to compare data sampled at points across an area defined by a grid you need to interpolate your sampled points to the grid first. – Spacedman Aug 21 '17 at 15:53
  • I know that and that's doable – Trina Aug 22 '17 at 3:16
  • Okay, so does my answer below answer your question? – Spacedman Aug 22 '17 at 9:19
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If you have netCDF support in your rgdal package you can do this.

First, some test data:

> library(sp)
> library(rgdal)
> library(raster)
> pts = data.frame(x=runif(50),y=runif(50),z1=rnorm(50),z2=rnorm(50))
> coordinates(pts)=~x+y
> projection(pts)="+init=epsg:4326"

Then use something like this:

> writeOGR(pts,"/tmp/test.nc",layer="pts", driver="netCDF")

This is not a grid, it is the raw x,y,z1,z2 data points.

> library(ncdf4)
> nc = nc_open("/tmp/test.nc")
> print(nc)

will show you the structure of the ncdf file.

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  • This will solve the problem for plotting in R as lat, lon are separate variables being stored. But this file is not plottable in other software like GRADS. – Trina Aug 23 '17 at 8:20
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A netcdf file do not have to be a grid. This can be a list of positions not regularly spread. You will have a vector of longitude, a vector of latitude and a vector of observations.
To plot it in R, you will need to use library ncdf4 for instance and extract vars of lat, lon and obs to create a spatial object to be plotted.

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  • But can I plot Lat, lon, time and value (in color) in a 4-d plot from an ungridded netcdf? – Trina Aug 21 '17 at 11:05

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