[ncl-talk] plotting model output where x/y are not lat/lon

Fri Aug 28 13:26:43 MDT 2015

Excellent, this worked!  Thank you!
I just have a quick follow-up question.  Once I assign the lat and lon to
my variables (for example:  sf at lon2d = lon2d, sf at lat2d = lat2d), and then
I would like to do a calculation with sf (eg. sf_total = dim_sum_n(sf,0)),
it seems I have to assign the the new variable the lat and lon again.  Is
there a way to keep the lat and lon following through the calculations
without always reassigning them?
I hope that makes sense.
Thanks,
Mira

> Here is more information about dat with 2-D coordinates.  I was typing
> this
> up when I saw Will's reply.  Some of the other examples indicate
> that trGridTrype may not be needed with some data sets.
>
> Please see section #2 on this documentation page, for a basic description.
> Notice the several different working examples:
> https://www.ncl.ucar.edu/Document/Graphics/overlays_on_map.shtml
>
> (Please ignore the link "2D vertical coordinates", that is not about
> geographic surface maps, and can be confusing.)
>
> The simplest example for making map plots with 2-D coordinates is example
> 3
> on this page:
> https://www.ncl.ucar.edu/Applications/ice.shtml
>
> I also like NARR example 4 because it shows how the 2-D coordinate method
> can be used with different map projections:
> http://www.ncl.ucar.edu/Applications/narr.shtml
>
> --Dave
>
>
> On Thu, Aug 27, 2015 at 9:35 PM, Will Hobbs <Will.Hobbs at utas.edu.au>
> wrote:
>
>> Mira
>>
>> It looks like you have 2-d lat and lon arrays associated with your data,
>> as is often the case with models (especially ocean models).
>>
>> This can be plotted by NCL without regridding, see the examples here:
>> http://www.ncl.ucar.edu/Applications/ease.shtml
>> Although you are not using the EASE grid, the principal is exactly the
>> same:
>>
>> 1. Set your map plot grid type resource
>> >res at trGridTrype = "TriangularMesh"
>>
>> 2. Set the lat and lon arrays as attributes of the array you are
>> plotting,
>> so if your array is 'x'
>> > x at lat2d = LAT
>> > x at lon2d = LON
>>
>> The just use one of the gsn_csm contour map plotting functions as
>> normal.
>>
>> I hope that's clear.
>>
>> Will
>>
>>
>> On 28/08/15 1:27 PM, "Yuqiang Zhang" <yuqiangzhang.thu at gmail.com> wrote:
>>
>> >Hi Mira,
>> >
>> >Check the link here
>> >http://www.ncl.ucar.edu/FAQ/
>> >For Q 27:
>> >
>> >When I call one of the gsn_csm_xxxx_map plotting scripts, I get an
>> error
>> >message about a units attribute not being correct.
>> >If you are using one of the gsn_csm_xxx_map functions to overlay data
>> on a
>> >map, and seeing one or both of the following error messages:
>> >
>> >    (0)   is_valid_lat_ycoord: Warning: The units attribute of
>> >    the Y coordinate array is not set to one of the allowable
>> >    units values (i.e. 'degrees_north'). Your latitude labels
>> >    may not be correct.
>> >
>> >    (0)   is_valid_lat_xcoord: Warning: The units attribute of
>> >    the X coordinate array is not set to one of the allowable
>> >    units values (i.e. 'degrees_east'). Your longitude labels
>> >    may not be correct.
>> >then this means that your data contains coordinate arrays, but the
>> >coordinate arrays either don't have the necessary "units" attribute, or
>> >it's
>> >not set to one of the allowable values ("degrees_east" for longitude
>> >values
>> >and "degrees_north" for latitude values).
>> >If your coordinate arrays are indeed degrees east and degrees north,
>> then
>> >you can set the units attribute as follows (this code snippet assumes
>> your
>> >data array is called "data" and that the coordinate arrays are called
>> >"lat"
>> >and "lon"):
>> >
>> >  data&lat at units = "degrees_north"
>> >  data&lon at units = "degrees_east"
>> >
>> >Regards,
>> >Yuqiang
>> >
>> >-----Original Message-----
>> >From: ncl-talk-bounces at ucar.edu [mailto:ncl-talk-bounces at ucar.edu] On
>> >Behalf
>> >Of mberdahl at envsci.rutgers.edu
>> >Sent: Thursday, August 27, 2015 10:21 PM
>> >To: ncl-talk at ucar.edu
>> >Subject: [ncl-talk] plotting model output where x/y are not lat/lon
>> >
>> >Hi all,
>> >
>> >I'm trying to make a simple plot of cumulative snowfall with data from
>> a
>> >model I did not run.  When I try to make a simple plot, I receive the
>> >following error:
>> >
>> >(0)     check_for_y_lat_coord: Warning: Data either does not contain a
>> >valid latitude coordinate array or doesn't contain one at all.
>> >(0)     A valid latitude coordinate array should have a 'units'
>> attribute
>> >equal to one of the following values:
>> >(0)         'degrees_north' 'degrees-north' 'degree_north' 'degrees
>> north'
>> >'degrees_N' 'Degrees_north' 'degree_N' 'degreeN' 'degreesN' 'deg north'
>> >(0)     check_for_lon_coord: Warning: Data either does not contain a
>> valid
>> >longitude coordinate array or doesn't contain one at all.
>> >(0)     A valid longitude coordinate array should have a 'units'
>> attribute
>> >equal to one of the following values:
>> >(0)         'degrees_east' 'degrees-east' 'degree_east' 'degrees east'
>> >'degrees_E' 'Degrees_east' 'degree_E' 'degreeE' 'degreesE' 'deg east'
>> >
>> >
>> >%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>> >
>> >When I dump the file it looks like this:
>> >
>> >netcdf ICE.1983.01-12.f77 {
>> >dimensions:
>> >        TIME = UNLIMITED ; // (365 currently)
>> >        X10_69 = 60 ;
>> >        Y18_127 = 110 ;
>> >        SECTOR = 2 ;
>> >        SECTOR1_1 = 1 ;
>> >        ATMLAY14_23 = 10 ;
>> >        bnds = 2 ;
>> >        ATMLAY23_23 = 1 ;
>> >        ATM6H3_3 = 1 ;
>> >        OUTLAY = 20 ;
>> >        OUTLAY1_1 = 1 ;
>> >
>> >variables:
>> >        double TIME(TIME) ;
>> >                TIME:units = "HOURS since 1901-01-15 00:00:00" ;
>> >                TIME:long_name = "time" ;
>> >                TIME:time_origin = "15-JAN-1901 00:00:00" ;
>> >                TIME:axis = "T" ;
>> >        float DATE(TIME) ;
>> >                DATE:units = "YYYYMMDDHH" ;
>> >                DATE:long_name = "Date(YYYY MM DD HH)" ;
>> >                DATE:history = "From ICE.f77.1983.01.01-15" ;
>> >        double X10_69(X10_69) ;
>> >                X10_69:units = "km" ;
>> >                X10_69:long_name = "x" ;
>> >                X10_69:point_spacing = "even" ;
>> >                X10_69:axis = "X" ;
>> >
>> > double Y18_127(Y18_127) ;
>> >                Y18_127:units = "km" ;
>> >                Y18_127:long_name = "y" ;
>> >                Y18_127:point_spacing = "even" ;
>> >                Y18_127:axis = "Y" ;
>> >        float LON(Y18_127, X10_69) ;
>> >                LON:units = "degrees" ;
>> >                LON:long_name = "Longitude" ;
>> >                LON:history = "From ICE.f77.1983.01.01-15" ;
>> >        float LAT(Y18_127, X10_69) ;
>> >                LAT:units = "degrees" ;
>> >                LAT:long_name = "Latitude" ;
>> >                LAT:history = "From ICE.f77.1983.01.01-15" ;
>> >
>> >Clearly there are lats and lons associated with the x and y spacing,
>> but
>> >I'm
>> >not sure how to tell NCL how to use those.  Does anyone have advice on
>> >this?
>> >
>> >Thanks in advance,
>> >Mira
>>
>