[Qgis-developer] Bug with floating point gains

[Matthew Hanson]

Thanks Nyall,

Sorry for the delay, I was at FOSS4G last week.   I tested this out and
confirms it is working now as intended.   Any clue on when it might be
available in a 2.8 update?

Thanks again!

matt

Matthew Hanson
Applied GeoSolutions
(603) 659-3363 x91
http://appliedgeosolutions.com
mhanson at appliedgeosolutions.com


On Thu, Mar 5, 2015 at 11:24 PM, Nyall Dawson <nyall.dawson at gmail.com>
wrote:

> On 5 March 2015 at 03:17, Matthew Hanson
> <mhanson at appliedgeosolutions.com> wrote:
> > Hello,
> >
> > I filed a bug report on this some weeks ago:
> > http://hub.qgis.org/issues/11573
> >
> > But it hasn't gotten the required attention.    It's a rather egregious
> bug,
> > which currently is restricting us to QGIS v2.2, which is becoming more
> of a
> > problem the more outdated it gets.
> >
> > In short, when using a floating point gain with integer images the
> datatype
> > is not promoted, so you end up with an image that is rounded to the
> nearest
> > integer.  It's fairly common practice to store indices, like NDVI, as an
> > Int16 with a gain of 0.0001 as it is half the space. But in QGIS, these
> > images end up being rounded to mostly 0.
> >
> > The feature of auto-applying the gain is nice in practice, but without
> > promoting the data type of the output it is counter-productive.   It
> would
> > be good to either revert this feature or properly promote the datatype.
> >
> > I'd be happy to do more digging and try fixing this and issue a PR if
> > someone could get me started by pointing me in the general direction of
> the
> > code responsible for this.
>
>
> This should be fixed in master now - can you please test and confirm?
> If so, I'll backport to 2.8.
>
> Nyall
>
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