eps and nscan in poisson_grid_fill

From: Jiaxin Zhang <jiaxinzhang3_at_nyahnyahspammersnyahnyah>
Date: Mon Aug 26 2013 - 21:01:35 MDT


Thank you for the information, Dennis.
Just an additional question about eps. In the poisson_grid_fill link, the
argument relc has a range of values, and I wonder if eps has also some
range of values (minimum and maximum). Or maybe eps can take any
value greater than 0?
I would need to make sure about this before experimenting with different
eps values in the code.
Is there any clue about what makes and eps value work better than another
one in the poisson_grid_fill function? How can I notice that one eps
improves the output of poisson_grid_fill with respect to a different eps

Thank you.

2013/8/25 Dennis Shea <shea@ucar.edu>

> You have to experiment.
> The eps for geopotential height is certainly different than that
> for (say) vorticity.
> Tha same eps should be used for each variable ... not 'year dependent'
> On 8/23/13 9:49 PM, Jiaxin Zhang wrote:
>> Dear NCL users,
>> I am using the function “poisson_grid_fill” for the first time and I have
>> some questions about the arguments of that function. I guess that this
>> function is only going to fill values in the grids with missing values,
>> without modifying those grids with already existant values, right?
>> Apparently, the “poisson_grid_fill” works very well with my data using the
>> same default values for the arguments provided in example 1 in the web
>> (see
>> attached code for temperature).
>> My questions are:
>> - It seems that the argument eps is variable dependent according to the
>> web. Do you think I can use the same eps value (for instance 1.e-2) for
>> all
>> my climate variables (temperature, rain, ...)? Or maybe is it necessary to
>> modify this depending on the approximate ranges of values for the climate
>> variables? I have included information about the ranges of my climate
>> variables for 1 year at the end of the message in case this may help.
>> Also,
>> because I have climate values for different years, I guess I could use the
>> same eps values for different years.
>> - I have tried nscan=1500, and it takes some time to complete the grid
>> filling for a netcdf with 2920 times. Do you think that when using a lower
>> value than 1500 for nscan it is going to be quicker to complete this part?
>> Or if it nscan is too low, perhaps then the results are not very reliable?
>> What are your suggestions?
>> Could anyone please have a look at the obtained plot with filled values
>> for
>> temperature from the script "test_grid_filling.ncl" and let me know your
>> opinion? Do I need to modify something in the script? I am not completely
>> sure about the most appropriate values for some of the arguments in the
>> function. Can I use the same argument values for all my climate variables?
>> With respect to the obtained results with this function, I am not
>> interested in the climate values located in water grids.
>> Thank you!
>> Jiaxin
>> -----------
>> In case it helps, the ranges and means of climate values for 1 year in my
>> netcdf files are, temperature (min=210, mean=282, max=325); longwave
>> radiation (min=56, mean=298, max=478); shortwave radiation (min=0,
>> mean=177, max=1119); specific humidity (min=1e-5, mean=0.0069,
>> max=0.02969); rain (min=0, mean=2.32e-5, max=0.00565); pressure
>> (min=56104,
>> mean=95094, max=106001); wind (min=2.05e-5, mean=2.87, max=25.46).
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Received on Mon Aug 26 21:01:48 2013

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