[Qgis-user] Re: Odd Null value

[Peter Ersts]

Agustin,

You will notice that that image does not have a valid NoDataValue by 
default, which is why the field in the properties dialog is blank.

The transparency table and NoDataValue field can handle scientific 
notation just fine. The problem is that -3.40282e+38 is NOT the "exact" 
value of the pixel, so the no data and transparency checks fail.

Overly simplistic example
( 3.2e+01 == 3.28 ) is false.

The "value tool plugin", if that is what you are using to find the 
values,  should let you choose between scientific notation and actual 
value for output display. Maybe the documentation or metadata for the 
project that produced that image will have a detailed description of 
pixel values.

-pete

Agustin Lobo wrote:
> I have a raster map
> (http://sedac.ciesin.columbia.edu/es/npp_geotiff.zip)
> with the odd value of
> -3.40282e+38
> as null value (this is probably the way some software is writing its 
> null values)
>
> Is there any way I can set this value as NO DATA VALUE in QGIS?
> I have the impression that the field in the Transparency tab does not 
> accept the e+38
> I've been able to set it in the transparency list thanks
> to the tool that lets you select in the image, but then
> cannot copy and paste.
>
> Thanks
>
> Agus


-- 
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Peter J. Ersts, Project Specialist
American Museum of Natural History
Center for Biodiversity and Conservation
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