[ncl-talk] Error in selecting box using coordinate subscripting

Mon Jul 19 22:37:39 MDT 2021

Dear Adam, Ushnanshu and others, 

Thanks a lot, It was a real help. I am thankful to the NCL community, its so helpful and quick. It has really encouraged me to use NCL more often. 

Sincere Regards 
Samir 

From: "Adam Phillips" <asphilli at ucar.edu> 
To: "Ushnanshu Dutta" <ushnanshudutta at gmail.com> 
Cc: "samirpokhrel" <samir at tropmet.res.in>, "ncl-talk" <ncl-talk at ucar.edu> 
Sent: Tuesday, July 20, 2021 2:00:39 AM 
Subject: Re: [ncl-talk] Error in selecting box using coordinate subscripting 

I cannot comment on the CDO alternative, but I do believe Samir's issue is resolvable without regridding especially as the grid is rectilinear. 
Samir: This should work: temp_et = temp({30:60},{-240:-170}) 
If you are not happy that the longitudes are all negative, you can do the following: 
temp_et = temp({30:60},{-240:-170}) 
lon = (/ temp_et&lon /) 
lon = lon+360 
lon!0 = "lon" 
lon&lon = lon 
temp_et&lon = lon 
printVarSummary(temp_et) 

That should show that the longitudes are positive, running from 120:190E. (As a rectilinear grid's coordinate latitude/longitude values should only monotonically increase, you cannot have values run from 120:180E, then flip around and go from -180:-170E.) 
Hope that helps! 
Adam 

On Mon, Jul 19, 2021 at 2:13 AM Ushnanshu Dutta < [ mailto:ushnanshudutta at gmail.com | ushnanshudutta at gmail.com ] > wrote: 

In continuation to my earlier email I forgot to mention the target grid file. I have created the target grid file like this 
cat > targetgrid << EOF 
gridtype = lonlat 
xsize = 360 
ysize = 180 
xfirst = −179.5 
xinc = 1 
yfirst = -89.5 
yinc = 1 
EOF 

here you also have options to change the resolution. 

On Mon, Jul 19, 2021 at 1:14 PM Ushnanshu Dutta < [ mailto:ushnanshudutta at gmail.com | ushnanshudutta at gmail.com ] > wrote: 

BQ_BEGIN

Dear Sir, 
Are you working with SST data from CMIP5 and CMIP6? Except for a few models , the SST data are provided on curvilinear grids. 

The following page can be your help 
[ https://www.ncl.ucar.edu/Applications/ESMF.shtml | https://www.ncl.ucar.edu/Applications/ESMF.shtml ] 

I think through cdo "remapbil" regridding from curvilinear to rectilinear (lon x lat) also possible. I have done that and compared with the original one and found they are consistent. Can somebody comment on this? 

On Mon, Jul 19, 2021 at 12:48 PM samirpokhrel via ncl-talk < [ mailto:ncl-talk at mailman.ucar.edu | ncl-talk at mailman.ucar.edu ] > wrote: 

BQ_BEGIN

Thanks Adam and Rashed, 

Its confusing, As LonPivot is just re-arranging the the order of Longitude start and end point, but the basic range is similar to that of the models original grid (i.e -279 to 80). 
Is it not possible to arrange the longitudes in the way its easy i.e positive means east and negative means west longitudes. 
Is re-gridding data the only solution? 

regards 
Samir 

From: "Adam Phillips" < [ mailto:asphilli at ucar.edu | asphilli at ucar.edu ] > 
To: "samirpokhrel" < [ mailto:samir at tropmet.res.in | samir at tropmet.res.in ] > 
Cc: "ncl-talk" < [ mailto:ncl-talk at ucar.edu | ncl-talk at ucar.edu ] > 
Sent: Friday, July 16, 2021 11:21:32 PM 
Subject: Re: [ncl-talk] Error in selecting box using coordinate subscripting 

Rashed is right, lonPivot is definitely one way to get around this issue. Another possibility is to just specify the area like this: 
temp_et = temp({30:60},{-240:-170}) 
Hope that helps! 
Adam 

On Fri, Jul 16, 2021 at 11:46 AM Rashed Mahmood via ncl-talk < [ mailto:ncl-talk at mailman.ucar.edu | ncl-talk at mailman.ucar.edu ] > wrote: 

BQ_BEGIN

lonFlip assumes that the central longitude is either Greenwich meridian (0) or 180 which is not the case in your data. Maybe "lonPivot" could do the job? 
[ https://www.ncl.ucar.edu/Document/Functions/Contributed/lonPivot.shtml | https://www.ncl.ucar.edu/Document/Functions/Contributed/lonPivot.shtml ] 
Or regriding the data could be another option. 

On Fri, Jul 16, 2021 at 8:55 AM samirpokhrel via ncl-talk < [ mailto:ncl-talk at mailman.ucar.edu | ncl-talk at mailman.ucar.edu ] > wrote: 

BQ_BEGIN

Dear NCL Users, 

I am having problem while selecting a specific region within model output global data. Model data Longitudes varies from -279.75 to 79.75. The printVarSummary of the model data is as follows 

------- 

Variable: temp 

Type: double 

Number of Dimensions: 2 

Dimensions and sizes: [YT_OCEAN | 410] x [XT_OCEAN | 720] 

Coordinates: 

YT_OCEAN: [-80.75..89.75] 

XT_OCEAN: [-279.75..79.75] 

--------- 

When I am trying to Select the region 120 E to 170W and 30N to 60N by using coordinate subscripting viz. 

temp_et = temp({30:60},{120:-170}) 

It is giving error like 

fatal:NclOneDValGetRangeIndex: start coordinate index out of range, can't continue 

fatal:Could not obtain coordinate indexes, unable to perform subscript 

Thereafter I have performed the lonFlip function 

temp_new = lonFlip(temp) 

temp_et = temp_new({30:60},{120:-170}) 

and the error is solved and the printVarSummary now looks like 

--------------------------- 

Variable: temp_et 

Type: double 

Number of Dimensions: 2 

Dimensions and sizes: [YT_OCEAN | 40] x [XT_OCEAN | 440] 

Coordinates: 

YT_OCEAN: [30.2501..59.75] 

XT_OCEAN: [119.75..-99.75] 

---------------------------- 

This is incorrect as my data is 0.5 degree resolution and X dimension should be 140 size rather than 440 size 

Please let me know where I am going wrong 

Thanking you in advance 

Regards 
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BQ_END

-- 
Adam Phillips 
Associate Scientist, Climate and Global Dynamics Laboratory, NCAR 
[ http://www.cgd.ucar.edu/staff/asphilli/ | www.cgd.ucar.edu/staff/asphilli/ ] 303-497-1726 

[ http://www.cgd.ucar.edu/staff/asphilli ] 

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BQ_END

-- 
Ushnanshu Dutta 
Research Fellow 
Indian Institute of Tropical Meteorology 
Pune,411008 
Mob: 9405022799 

BQ_END

-- 
Ushnanshu Dutta 
Research Fellow 
Indian Institute of Tropical Meteorology 
Pune,411008 
Mob: 9405022799 

BQ_END

-- 
Adam Phillips 
Associate Scientist, Climate and Global Dynamics Laboratory, NCAR 
[ http://www.cgd.ucar.edu/staff/asphilli/ | www.cgd.ucar.edu/staff/asphilli/ ] 303-497-1726 

[ http://www.cgd.ucar.edu/staff/asphilli ] 

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