[Qgis-user] NoData

[Niccolò Marchi]

Bernd and Matt: thank you very much for answering.
still the ideas are quite confused but your help gave a chance for understanding ;)

any further suggestion from other users is well accepted!

all the best,
Nic





Date: Wed, 15 Oct 2014 12:24:09 +1100
Subject: Re: [Qgis-user] NoData
From: mattslists at gmail.com
To: bernd.vogelgesang at gmx.de
CC: qgis-user at lists.osgeo.org; sciurusurbanus at hotmail.it

I can contribute a couple of things from my experience with some of these.1. there are some gotchas with using NULL (in vector files) is that the result of X+NULL or X concatenate NULL, effectively any operation using NULL the result is NULL. This is expected/deliberate.I've only come across Nan in tiffs when there's somethings wrong with the format / import.Nodata seems to be specified, the default is set at 0 on most files/formats I've dealt with (usually single band rasters) and its handled the same way as if I specify -999.
Matt



On Wed, Oct 15, 2014 at 10:39 AM, Bernd Vogelgesang <bernd.vogelgesang at gmx.de> wrote:




This post seemes to have drowned, so I dare to bump it, hoping that some less confused people like me might anwser to it.I'm using QGIS for years now, but I never figured out how that stuff is supposed to work.One of the reasons why I try to do a lot of stuff now in R is that NA is NA !
Am 08.10.2014, 11:27 Uhr, schrieb Niccolò Marchi <sciurusurbanus at hotmail.it>:

hi all!
please, is there someone who could explain properly all the "NoData topic"?

I mean:
1. differences in setting negative values (-999, -9999, -3.40282e +35, etc) VS NoData (Nan, NoData, NULL)
2. how QGIS handles it
3. "best practices" or good hints for managing them

sorry but I've quite a big confusion.

Thank you very much in advance!

Nic
 		 	   		  


-- Bernd Vogelgesang
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Tel: 09133-825374
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