[Qgis-developer] Bug with floating point gains

[Matthew Hanson]

Hi, I was wondering if this fix could be backported to 2.8 (or even all
affected versions which is everything later than 2.2).   We are currently
still running 2.2, but it's becoming more of a problem as plugins stop
working, dependencies get upgraded, etc.

Thanks!

matt

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


On Tue, Mar 17, 2015 at 12:15 PM, Matthew Hanson <
mhanson at appliedgeosolutions.com> wrote:

> 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 problem the more outdated it gets.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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