retrieve.nc {clim.pact}R Documentation

Retrieve data from a netCDF file

Description

Reads a netCDF file and picks out vectors that look like lngitude, latitude and time. Returns the first 3-D field in the file. See also cdfextract (large data files).

This version uses cdfcont to obtain vital meta data for handling the data in the netCDF file and constructing a 'field' object.

This routine unfortunately only currently works on Linux platforms since the ncdf-package is only available for Linux systems.

Usage

retrieve.nc(filename=file.path("data","ncep_t2m.nc"),v.nam="AUTO",
                        l.scale=TRUE,greenwich=TRUE,
                        x.nam="lon",y.nam="lat",z.nam="lev",t.nam="tim",
                        x.rng=NULL,y.rng=NULL,t.rng=NULL,force.chron=TRUE)

Arguments

filename name of netCDF file.
v.nam name of variable. "AUTO" -> smart search.
l.scale 'TRUE' uses scaling.factor and add.offset.
greenwich 'TRUE' centres maps on Greenwhich meridian (0 deg E).
x.nam Name of x-dimension.
y.nam Name of y-dimension.
z.nam Name of z-dimension.
t.nam Name of time-axis.
x.rng Region to extract.
y.rng Region to extract.
t.rng Time interval to extract.
force.chron Check for monotonic chronological order (no jumping back and forth in time).

Value

A "field.object" list:
dat a 3-D matrix with the data.
lon a vector of longitudes.
lat a vector of latitudes.
tim a vector of times from time.0 (see attributes).
lev a vector of vertical levels (NULL for single level).
v.name variable name.
id.x ID labels for the spatial grid (for mixed fields, see mixFields).
id.t ID labels for the time axis (for combined fields).
yy a vector of years corresponding to tim.
mm a vector of months corresponding to tim.
dd a vector of days corresponding to tim.
n.fld number of fields (for mixed fields, see mixFields).
id.lon ID labels along the longitudes (for mixed fields, see mixFields).
id.lat ID labels along the latitudes (for mixed fields, see mixFields).
.

Author(s)

R.E. Benestad

Examples

## Not run: 
X.1 <- retrieve.nc("data/mpi-gsdio_t2m.nc",
                   x.rng=c(-60,40),y.rng=c(50,75))
X.2 <- retrieve.nc("data/mpi-gsdio_slp.nc",
                   x.rng=c(-60,40),y.rng=c(50,75))

# The definition of a 'field' object is:
ny<-length(slp$lat); nx<-length(slp$lon)
slp  <- list(dat=X.2$dat,lon=X.2$lon,lat=X.2$lat,tim=X.2$tim,lev=X.2$lev,
             v.name=X.2$v.nam,id.x=X.2$id.x,id.t=X.2$id.t,
             yy=X.2$yy,mm=X.2$mm,dd=X.2$dd,n.fld=1,
             id.lon=rep(X.2$v.name,nx),id.lat=rep(X.2$v.name,ny),
             attributes=dat.att)
 class(slp) <- c("field")

## End(Not run)
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