[Qgis-user] unable to produce a raster mask

[Giacomo]

Dear Giuseppe

First I have to apologize for the big delay I used to reply you.

Your hint was correct and the map is done.

Thank you very much again!

Spero di rivederti presto.

Giacomo
On 24/11/2014 00:20, Giuseppe Sucameli wrote:
> Ciao Giacomo,
>
> the condition ( "lc_n_italy1 at 1" >= 8 ) is evaluated to either 1 or 0 
> depending on the lc_n_italy1 at 1 value.
> so you always get 0 (!) as the second factor is always 0.
>
> Try to set the formula to the following:
> ( "lc_n_italy1 at 1" < 8 ) * "lc_n_italy1 at 1
>
> Best regards.
> Giuseppe
>
>
> On Sat, Nov 22, 2014 at 11:34 AM, Giacomo Fontanelli 
> <giacomofontanelli76 at gmail.com <mailto:giacomofontanelli76 at gmail.com>> 
> wrote:
>
>     Dear community
>
>     I start from a raster layer, 8bit unsigned integer. Pixel value
>     ranges from 1 to 12.
>
>     I would like to mask the pixels with value>8, setting their new
>     value to 0.
>
>     I used raster calculator with this formula
>
>      ( "lc_n_italy1 at 1" >= 8 )  * ("lc_n_italy1 at 1" * 0)
>
>     I tried also
>
>      ( "lc_n_italy1 at 1" >= 8 )  * 0
>
>     but I always obtain a map with only "Nan"
>
>     Can you help me?
>
>     Thank you
>
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>
>
>
>
> -- 
> Giuseppe Sucameli

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