[GRASS5] how to NULL in site lists?

Eric G . Miller egm2 at jps.net
Tue Jan 23 21:07:19 EST 2001

On Tue, Jan 23, 2001 at 09:59:47PM +0000, 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?

We've discussed this before.  I don't know that modules will treat -0.0
appropriately (most likely they'll just treat it like zero).  IMHO, the
whole conception of the sites format sucks from both a user's and a
programmer's perspective.  When we get proper tabular data support built
into GRASS, this problem should be easy to handle.  But that's going to
be a while, and I for one have yet to put my "money" where my mouth is
;)  Hopefully, in 5.1 we can solve this.  I don't think using -0.0 will
do much at this point, since most sites modules have some fundamental
assumptions about the data they are reading (which includes it not being
NULL and not being NaN).  Also, this doesn't address NULL string values.

Sorry if I'm kind of a spoiler on the quick fix, but I think fundamental
changes are required.

Eric G. Miller <egm2 at jps.net>

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