[Qgis-developer] min/max for rasters

[Paolo Cavallini]

Il 13/12/2013 20:18, Radim Blazek ha scritto:

>> Can you describe some examples where 2-98% is a problem (data type,
>> number of bands, map content, features/phenomena represented by those
>> 2+2%,...) so that we can think about it better?

Example #1 (less problematic): dtm and their legend are always shown
wrong; newbies do not understand why
Example #2 (more serious): rasterizing sparse vectors (e.g. rivers)
results in a black rectangle, as the number of pixels with valid data is
<2%.

In fact, I think we should help users more, e.g. by applying non linear
colour scaling (log, exp)  in case of very skewed raster values
distribution: if data are more or less normally distributed, no cut is
applied, and linear scaling is used; if they are badly skewdw or with
outliers, apply a non linear colour scaling. With some thinking, this
should solve most if not all user cases, without asking a normal user to
understand much about raster stats.

However, in my case the general setting "use min/max" does not seem to
be working.
Thanks for your thoughts.

-- 
Paolo Cavallini - www.faunalia.eu
QGIS & PostGIS courses: http://www.faunalia.eu/training.html