[ncl-talk] NDVI_mask problem

[Dennis Shea]

If you go to NCL's Examples page:

   https://www.ncl.ucar.edu/Applications/

Under 'Datasets', click 'NDVI'

There are three examples of differently sourced NDVI data sets.

The 'GIMMS' version is Example 2.

Please read the associated text description and the actual script.
As noted, the netCDF file is poorly written.



On Wed, May 9, 2018 at 8:14 AM, Mary Haley <haley at ucar.edu> wrote:

> Hi Jalal,
>
> I took a look at one of these NDVI data files, and noticed that the
> lat/lon coordinate arrays on the file have no attributes, which is not good.
>
> These arrays should at least have "units" and "long_name" attributes and
> units should be something like "degrees_north" and "degrees_east".  For
> rectilinear data (data with lat/lon coordinate arrays), NCL needs these
> units to be something that indicates they are in degrees, or otherwise it
> can't be sure it is plotting the data correctly.
>
> It's always important to look at your data when you get errors like this.
> You do have:
>
> printVarSummary(ndvi)
>
> but I also added:
>
> printVarSummary(ndvi&lat)
> printVarSummary(ndvi&lon)
>
> in order to look at the lat/lon arrays to see what the units were and you
> can see there are none:
>
> Variable: lat (coordinate)
> Type: double
> Total Size: 17280 bytes
>             2160 values
> Number of Dimensions: 1
> Dimensions and sizes: [lat | 2160]
> Coordinates:
> Number Of Attributes: 0
>
>
> To fix this, I did this after reading in ndvi:
>
>   ndvi           = f->ndvi(0,:,:)
>   ndvi&lat at units = "degrees_north"    ; Fix the units
>   ndvi&lon at units = "degrees_east"
>   printVarSummary(ndvi)
>
> I also had to remove the reference to "ndvi at long_name" in a later title
> string, because ndvi doesn't have a long_name attribute.
>
> --Mary
>
> On Wed, May 9, 2018 at 3:44 AM, Md. Jalal Uddin <dmjalal90 at gmail.com>
> wrote:
>
>> Hi all,
>>
>> I tried to plot gimms ndvi (https://ecocast.ar
>> c.nasa.gov/data/pub/gimms/3g.v1/) data by masking. I am getting
>> following errors. I used  copy_VarCoords(ndvi,ndvi_mask) command to fix
>> it but failed. Please help to solve this problem. Please find my script in
>> the attachment.
>>
>> (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'
>> (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'
>> warning:Attempt to reference attribute (long_name) which is undefined
>>
>> Cheers,
>> Jalal
>> --
>> *Md. Jalal Uddin*
>> MSc in Applied Meteorology (English Language)
>> Nanjing University of Information, Science and Technology, China
>> Jasmine Jiangsu Government Scholar
>> Cell: +8613260859092
>> Office: Beichen Building, School of Geography and Remote Sensing, Room
>> No. 406
>>
>> *AND *
>> B.Sc. in Disaster Management (Hons.)
>> Patuakhali Science and Technology University, Bangladesh.
>> Cell: +8801792052662, +8801838613203
>> Email: dmjalal90 at gmail.com
>> Web: www.dmjalal90.weebly.com
>> Facebook: jalal.hossen.39
>> LinkedIn: https://bd.linkedin.com/in/md-jalal-uddin-80a026b0
>> Twitter: dmjalal90
>> Skype: dmjalal90
>>
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>
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