[GRASS5] how to NULL in site lists?

[Andreas Lange]

Hi Markus, Hi all,

i agree with Eric and Roger that the quick fix is not advisable.

But there is another more general consideration to the NULLs in site
lists.
IMHO the site list format is for the storage of point data derived from
measurements.  Usually the points are irregularily spaced. The site list
contains the spatial data (coordinates) and the attribute(s) in a sort
of 1:1 database. So if you have no value (measurement) at a given point,
there should be no site list entry/line. 
The problem comes from changing the sites format from one attribute to
several attributes. This can not be modelled adequate with a 1:1
database structure. 
Another approach would be to create a site list for each
attribute/variable and to ommit the sites where no measurement/variable
value is available (NULL attributes). I don't know if NULL values with
site files are conceptually correct. 

Sorry, i am not able to explain this in better english.

cu,

Andreas

Markus Neteler wrote:
> 
> Hi all,
> 
> as working with sites at time, I face the problem that I
> don't knwo how to code null values in a site_list.
> (Eric, we already talk once about this weeks ago).
> 
> As we cannot simply invent a special character for
> this (maybe to complex to change the entire sites lib),
> what about using for GRASS 5.0 the value -0.0?
> 
> Just an idea. Or is there another way?
> Using -9999 like ESRI does is of course unwanted and
> currently leads to nonsense results (as it is treated
> as true value).
> 
> As -0.0 is currently also treated as true value, I
> would like to know if it could become a workaround unless
> it is improved in 5.1?
> 
> Markus
> 
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-- 
Andreas Lange, 65187 Wiesbaden, Germany, Tel. +49 611 807850
Andreas.Lange at Rhein-Main.de - A.C.Lange at GMX.net



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