[Qgis-user] Cumulative count cut on rasters

[Radim Blazek]

On Wed, Aug 12, 2015 at 3:07 PM, Andrea Peri <aperi2007 at gmail.com> wrote:
> Hi Radim, thx for explain.
> Your explanation of extimated strategy could explain why the extimated
> is more precise rather than the actual strategy.
> I guess are the null values to produce a wrong "actual" results.
>
> Can you say me in which file I can found the code for the extimate and
> actual strategy
> to verify my hypotesis.?

https://github.com/qgis/QGIS/blob/master/src/core/raster/qgsrasterinterface.cpp#L395
https://github.com/qgis/QGIS/blob/master/src/providers/gdal/qgsgdalprovider.cpp#L1323
https://github.com/qgis/QGIS/blob/master/src/core/raster/qgsrasterinterface.cpp#L510

Radim


> Thx.
>
>
>
> 2015-08-12 11:22 GMT+02:00 Radim Blazek <radim.blazek at gmail.com>:
>> 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
>>> -----------------
>>> _______________________________________________
>>> Qgis-user mailing list
>>> Qgis-user at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/qgis-user
>
>
>
> --
> -----------------
> Andrea Peri
> . . . . . . . . .
> qwerty àèìòù
> -----------------