[gradsusr] strmden/skip

[Jennifer M Adams]

> On Jan 12, 2018, at 3:45 PM, sim.aberson <sim.aberson at noaa.gov> wrote:
> 
> With lterp, don't I need another gridded field at a lower resolution as the destination (dest)?  I don't have that, just the fields at the 0.02-degree resolution.

You can open a second file that has a coarser grid. You can use a dummy descriptor like what I copied below, setting XDEF and YDEF to be whatever you want, then use the internal variable ‘lon’ or ‘lat’ in the lterp() expression for the destination grid.  
dset ^foo.bin
options template
undef -9.99e8
xdef 90 linear 2 4
ydef 45 linear -88 4
tdef 1 linear 01Jan0001 1dy
zdef 1 linear 1 1
vars 1
foo 0 99 foo
endvars


> 
> I tried strmden X where x is between -10 and 0.  There really isn't much difference between any of them.


> Thanks,
> Sim
> 
> On 1/12/18 10:35 AM, Jennifer M Adams wrote:
>> Use the lterp() function to coarsen the grid of your wind fields to spread out the streamlines. You might also try tweaking the spatial domain a little bit, or playing with other strmden values  — try using -8 or -2 to see how that affects things. My recollection is that -1 to -10 is not necessarily a linear path in the same way that 1 to 6 is, but it’s been a while since I played with high-res streamlines. —Jennifer
>>> On Jan 12, 2018, at 9:53 AM, sim.aberson <sim.aberson at noaa.gov> wrote:
>>> 
>>> Thanks for the response.  Yes, I want to overlay fields on the wind field, and there are far too many streamlines to see anything with set strmden -10.
>>> 
>>> This then brings up the question, is there a way to regrid within grads 2.0+, or do I need to regrid with some other code and then use the regridded files to plot.  I could not find anything in the grads documentatoin about regridding.
>>> 
>>> Thanks.
>>> 
>>> On 1/12/18 6:09 AM, Davide Sacchetti wrote:
>>>> no chance using skip: use strmden
>>>> if strmden is not "strong" enough you could regrid your data on the fly
>>>> to coarser resolution and plot regridded data
>>>> bye bye
>>>> Davide
>>>> On Thu, 2018-01-11 at 15:58 -0500, sim.aberson wrote:
>>>>> I have a high-resolution wind analysis
>>>>> 
>>>>>   XDEF    501   LINEAR   -5.00000    0.02000
>>>>>   YDEF    401   LINEAR   -4.00000    0.02000
>>>>> 
>>>>> When I plot using
>>>>> 
>>>>>    'set gxout stream'
>>>>>    'set strmden -10'
>>>>>    'set cint 5'
>>>>>    'set clevs  5 10 02 20 25 30 35 40 45 50 55 60 65 70 75 80'
>>>>>    'set ccols  9 14  4 11  5 13  3 10  7 12  8  2  6  9  5 10'
>>>>>    'd urel;vrel;mag(urel,vrel)'
>>>>> 
>>>>> I get the attached.  I want even fewer streamlines than that, but
>>>>> the
>>>>> documentation states that density is between -10 and 10.
>>>>> 
>>>>> I tried to use skip, but that seems to only work for arrows and
>>>>> barbs,
>>>>> not streamlines.  I tried to create new variables using something
>>>>> like
>>>>> 
>>>>>    'define uskip=skip(urel,2,2)'
>>>>>    'define vskip=skip(vrel,2,2)'
>>>>>    'd uskip;vskip;mag(uskip,vskip)'
>>>>> 
>>>>> and I tried
>>>>> 
>>>>>    'd
>>>>> skip(urel,2,2);skip(vrel,2,2);mag(skip(urel,2,2),skip(vrel,2,2))'
>>>>> 
>>>>> and got the same thing for both, a blank plot.
>>>>> 
>>>>> Any suggestions?
>>>>> 
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>> --
>> Jennifer Miletta Adams
>> Center for Ocean-Land-Atmosphere Studies (COLA)
>> George Mason University
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> 
> 

--
Jennifer Miletta Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
George Mason University