Hi Jianhua: sometimes these datasets have a "nodata flag" that will be
stored as (often) a large negative number that you need to be aware of
before you start working with the data.  I would recommend looking a bit
more carefully at the documentation for the outputs.  The other possibility
is that the model has a bug, so you need to investigate that and possibly
report back to the modeler.

Are there clear spatial patterns as to where the negative numbers show up?

--j


On Mon, Feb 11, 2013 at 5:01 PM, Jianhua Huang <jh.eco.cas@gmail.com> wrote:

> Hi all:
>
>
>
> I am using the precipitation (pr) data from rcm3-cgcm3 model. I used the
> ncdf4 package to open the precipitation data. Some values are very close to
> zero, for example 3*10^(-23),  and there are even some negative values
> (like
> -3*10^(-21)). Should I treat these values as zero? I don't know whether
> this
> problem is caused by the R.  Anybody knows what cutoff should I choose for
> the float point data?
>
>
>
> Thanks
>
>
>
> Jianhua
>
>
>
>
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>
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-- 
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
607 South Mathews Avenue, MC 150
Urbana, IL 61801
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307, Skype: jgrn3007

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