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rotated_pole remapped for use in a GIS

Added by Laura Brown about 10 years ago

Hello,
I'm new to NETCDF data sets and am having difficulty finding a way to bring them into a GIS in a format compatible with landuse landcover data, habitat data and ecozone data. I have downloaded CANRCM4 data sets covering the CORDEX North America region. The spatial coordinates are in rotated_grid with the north pole longitude = 83f and the latitude = 42.3f. I have been trying to figure this out and asked the contacts at the CCCma, some GIS folks and scoured the internet but can't find a way to take these data and work with it in a GIS. It seems that many folks are looking for these answers but they too are having difficulty finding them. Someone at the CCCma suggested I use CDO. I have install the WIN32 version and read several queries and the manual. I understand that you can remap but that you need the to define the the coordinates of the TLC in the new system.
I don't know where to find the x and y coordinates for other systems.
Does anyone know where I could find this information? Or has anyone converted these files into Geographic of Projected coordinate system?
Thank you for your time
There's the metadata:
tasmax_NAM-22_CCCma-CanESM2_rcp85_r1i1p1_CCCma-CanRCM4_r2_day_20060101-20101231.nc

dimensions:
time = UNLIMITED ; // (1825 currently)
rlon = 310 ;
rlat = 260 ;
bnds = 2 ;
variables:
double time(time) ;
time:long_name = "time" ;
time:standard_name = "time" ;
time:units = "days since 1949-12-01" ;
time:axis = "T" ;
time:calendar = "365_day" ;
time:bounds = "time_bnds" ;
double time_bnds(time, bnds) ;
double rlon(rlon) ;
rlon:long_name = "longitude in rotated pole grid" ;
rlon:units = "degrees" ;
rlon:axis = "X" ;
rlon:standard_name = "grid_longitude" ;
double rlat(rlat) ;
rlat:long_name = "latitude in rotated pole grid" ;
rlat:units = "degrees" ;
rlat:axis = "Y" ;
rlat:standard_name = "grid_latitude" ;
double lon(rlat, rlon) ;
lon:long_name = "longitude" ;
lon:units = "degrees_east" ;
double lat(rlat, rlon) ;
lat:long_name = "latitude" ;
lat:units = "degrees_north" ;
char rotated_pole ;
rotated_pole:grid_mapping_name =
"rotated_latitude_longitude" ;
rotated_pole:grid_north_pole_longitude = 83.f ;
rotated_pole:grid_north_pole_latitude = 42.5f ;
float tasmax(time, rlat, rlon) ;
tasmax:long_name = "Daily Maximum Near-Surface Air
Temperature" ;
tasmax:standard_name = "air_temperature" ;
tasmax:units = "K" ;
tasmax:cell_methods = "time:maximum" ;
tasmax:coordinates = "lon lat" ;
tasmax:grid_mapping = "rotated_pole" ;
tasmax:_FillValue = 1.e+20f ;


Replies (6)

RE: rotated_pole remapped for use in a GIS - Added by Jaison-Thomas Ambadan about 10 years ago

I don't know where to find the x and y coordinates for other systems.

If you know the lat-lon boundaries and approximate grid step/increment, then you just need to provide that in the grid description (for remap). If it is a global data then you could try, for example:

cdo -remapbil,r360x180 ifile.nc ofile.nc

will remap to a global 1 degee regular lon-lat grid. For half a degree resolution, use r720x360 etc.

The following thread may help you: https://code.zmaw.de/boards/1/topics/2632?r=2634#message-2634

Cheers,
J

RE: rotated_pole remapped for use in a GIS - Added by Laura Brown about 10 years ago

Hi J,
Thank you for your speedy response.
I tried:
cdo -remap,r360x180 iflie ofile
and get:
cdo remap <Abort>: too few arguments! Need 2 found 1.

I then tried:
cdo -f nc remapcon,r360x180 iflie ofile
based on the code in the link you suggested but that causes cdo.exe to stop working (windows pop up box)

Do you have any suggestions?
Thank you for your time

RE: rotated_pole remapped for use in a GIS - Added by Jaison-Thomas Ambadan about 10 years ago

[sorry, I'll edit that] you have to specify the remap method or provide the weights. The command should be

cdo -remapbil,r360x180 ifile ofile

this will use bilinear interpolation. Please have a look at the REMAP section of CDO documentation for more info regarding tge available methods.

Cheers,
J

RE: rotated_pole remapped for use in a GIS - Added by Laura Brown about 10 years ago

Thanks,
I read through the documentation sections and tried several iterations/attempts of both the 'weights' operations and the 'remap' operations but cdo.exe appears to be unstable
For example:
cdo -remapbil,r360x180 ifile ofile or any remap operation results in cdo.exe crashing
cdo -genbil,target.txt ifile ofile results in cdo.exe crash too

I'm now trying to learn how to use the cygwin interface to compile another version of CDO.

I appreciate your help and will let know if I figure out how to build and use CDO in this alternate environment

RE: rotated_pole remapped for use in a GIS - Added by Jaison-Thomas Ambadan about 10 years ago

Hi,

If there is any error/warning/crash message, please post it (along with the output of "cdo -V", Windows version and platform 32/64 bit) in CDO win32 Feedback forum https://code.zmaw.de/projects/cdo/boards/4 If there is a bug it may help to solve the problem.

Unfortunately I do not have any experience using CDO in Windows environment.

Cheers,
J

RE: rotated_pole remapped for use in a GIS - Added by Laura Brown about 10 years ago

Hi,
I have installed cgywin and CDO-1.6.4 and can now remap the netcdf ifiles to ofiles. The next step is to figure out how to take these ofiles and register them with GIS data covering a part of the spatial extent correctly.
Any suggestions would be welcome.
Thanks for all you help,
Laura

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