[Qgis-user] Cumulative count cut on rasters

[Radim Blazek]

On Tue, Aug 11, 2015 at 3:09 PM, Andrea Peri <aperi2007 at gmail.com> wrote:
> Hi,
> trying the rendering of a raster floating point using the cumulative count cut.
> I see it is quite good if I set the values 2.0,100.0% (not 98%) and
> use the accuracy at value "estimate".
> Instead always with the same values for cumulative count cut, but
> using the accuracy "actual".
> The result is really poor. The image became totally black with only
> few isles of grey.
>
> This is a surprise for me because the accuracy "actual" take a long
> time and the name seem to say more precision.
>
> I like to know what is the strategy used for actual: estimate and the
> strategy for accuracy: actual.

Actual takes all pixels, estimate takes 250000 pixels (whole data
extent with resolution giving approximately 250000 pixels). Some
providers may use different approach to get estimated values, e.g.
GDAL provider may use approximated values returned by GDAL, IIRC.

Radim


>
> Many thx.
>
> --
> -----------------
> Andrea Peri
> . . . . . . . . .
> qwerty àèìòù
> -----------------
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