Problem with raster package and nc4 file

Hi,

I have daymet data in nc4 format and could open it with the ncdf4 package.
I also have the coordinates of some polygons representing ecological areas.
Both, the polygon vertices and the nc4 file have the same projection (LCC)
and units (degrees).
Do you have grid data in LCC but stored with longitude/latitude
coordinates? This is unfortunate, but you can restore the LCC grid
probably. I would try

r <- raster("tmin_1980.nc4")

and then print it out and tell us the result (or post the errors if it
fails):

r

Do you have the details of the LCC projection? At a bare minimum you need
the centre longitude and centre latitude, and the two standard parallels,
and the datum/ellipsoid.  Can you open the file with ncdf4 and print out
this?

ncic <- nc_open("tmin_1980.nc4")
print(ncic)

 You are not supposed to mix use of the ncdf4 package functions with those
of raster, raster is designed to do all the work - but it does expect
sensibly specified regular grids.  If your data really are regular in LCC I
would recommend sorting that out. Can you share the file, or a link to an
analogous one?

Once you have it sorted out in raster, you can read your shapefile in and
do this

meanpolydata <- extract(r, poly, fun = mean)

Cheers, Mike.

What I would like to do is to get the average temperature for each
ecological area. So I wanted to use the polygons as a mask for the
temperature raster and then get the average temperature for each polygon.

I wanted to create a raster object (using the raster function in the
raster package):

ncic <- nc_open("tmin_1980.nc4")
raster(ncic, 'tmin')

But I get this error:
Error in (function (classes, fdef, mtable)  :
  unable to find an inherited method for function ?raster? for signature
?"ncdf4"?

Does anyone know how to fix this? Is there another way to get the data
that I need?

I am a bit confused by the fact that the temperature data consists of one
matrix with latitude data, one with longitude data and one with the
temperature values. And by the fact that the spacing between the latitude
and longitude matrices is not uniform. Is the raster package accounting
somehow for this?

Thanks a lot. Andi.

_______________________________________________
R-sig-Geo mailing list
R-sig-Geo at r-project.org
https://stat.ethz.ch/mailman/listinfo/r-sig-geo

Problem with raster package and nc4 file

Thread (6 messages)