data help

[Arlindo da Silva]

2008/6/9 Fredrick Mashingia <fmashingia at yahoo.com>:
>
> Hi,
>
>
>

First of all, please do not send questions like this directly to me. Always
send it to the "gradsusr" list. Two reasons: 1) generally there are
more knowledgeable people out there that may have direct experience with
your problem, and 2) in case I know the answer, the list provides a
searchable resource for future reference by other users.



> I am trying to appy the GSMaP-TMI hourly precipitatition data(in grads
> format) over Africa and I can display the data( for the events of 19th to
> 22nd April 1999,28th to 30th April 1999 and 14th to 18th May 1999) using
> GrADS 1.9b4 in FC5 OS machine. I would like to ask if it is possible to
> extract time series data (in text format) from each GrADS lat/lon grids in
> my 52 sq.km catchment located between lon 37019'08''E and 37024'15''E, and
> lat 3004'33''S to 3017'14''S at an elevation between 1000masl and 5895masl
> (the summit of Mt.Kilimanjaro).
>

Have you had a chance to search "gradsusr" about this? It is unfortunate
that "gradsusr" requires people to register in order to search it, but you
will be surprised how much information you can find there. For this
particular issue (writing ASCII), the answer is "yes". While you "set gxout
fwrite" to write binary files, you "set gxout print" to produce ASCII
output. The documentation can be found here:

      http://grads.iges.org/grads/gadoc/gradcomdsetprnopts.html



> And also if it is possible to change the GrADS lat/lon grids into match
> with my model grid resolution.
>

You have several options for "regridding" data from one resolution into
another. For smooth, continuous fields linear or even cubic interpolation
works fine. For discontinuous fields such as precipitation you may want to
use a "box averaging" or "mass conserving" scheme. In the GrADS v1.9 series
these are implemented by the classic user defined function "regrid2" in
GrADS v1.9b4 and older, or by the "re" extension available with the
OpenGrADS extensiona in v1.9-rc1:

     http://opengrads.org/wiki/index.php?title=User_Defined_Extensions

In particular the man page:

     http://opengrads.org/doc/udxt/re/

You can download v1.9-rc1 and extensions from the OpenGrADS sf.net area:

    http://sourceforge.net/project/showfiles.php?group_id=161773

As of this writing, GrADS v2 only offers a linear interpolation option by
means of the built in function lterp().


> I understand the two operations can be done under ArcView environment easly
> but then I dont know how one can convert grads data into arcview shapefiles.
> Please if you can help I should be very grateful.
>

As of now there is no shapefile output capability in GrADS, although some of
us have started working on it. In any case, I am not sure one would use
shapefiles, which is often used to write out "vector graphics" (lines,
filled polygons, etc), to output gridded data. I never used ArcView myself,
but I wonder if it cannot read regular binary or netcdf files. Does anybody
know? If so, can you post a mini "how-to" to the list?

  Good Luck,

        Arlindo


--
Arlindo da Silva
dasilva at alum.mit.edu
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