[Qgis-developer] No data value in raster transparency list

[Radim Blazek]

On Fri, Aug 24, 2012 at 10:49 AM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
> Hi Radim
>
> I don't have a strong opinion about wether to show nodata value in
> transparency list in the GUI or not. After all, the renderer sees only the
> transparency list and does not care which of them is the nodata value
> (except for the decision if the renderer is using transparency or not).

As I removed nodata from transparency list, I also added nodata check
to renderers.

> If you think it is a big useability plus to hide that from the user, that's
> ok for me.

It is a bit confusing I think, especially with no data values added
internally by QGIS (out of data range). But especially it would be
problem if for example, original data type is integer, but QGIS
internally uses float, in that case it would not be possible to use
QIntValidator in transparency list.

>> we have to add support for it in GUI (set color)
>> and renderers. Currently there is no such support.
>
> There is. If you e.g. have -9999 as nodata value and configure singleband
> pseudocolor renderer to render this as red, you can do it in the dialog.

Yes, but with gray and RGB?

Radim

>> There are other standard ways to highlight nodata:
>> - set background color
>> - set nodata pixels to a different value (r.null) and assign a color to it
>
> Yes, but it is less convenient. But nodata analysis does not happen to often
> for me, so I could live with a workaround.
>
> Regards,
> Marco
>
> Am 23.08.2012 13:59, schrieb Radim Blazek:
>
>> On Thu, Aug 23, 2012 at 8:15 AM, Marco Hugentobler
>> <marco.hugentobler at sourcepole.ch> wrote:
>>>
>>> Hi Radim
>>>
>>> Nodata should be rendered transparent in most cases. But it could also be
>>> possible you want to render it differently. E.g. the interpolation plugin
>>> writes nodata value in case it encounters numerical problems. Then it is
>>> useful to have the nodata values coloured to see where problems happened.
>>
>> There are other standard ways to highlight nodata:
>> - set background color
>> - set nodata pixels to a different value (r.null) and assign a color to it
>>
>> If you and other users insist that it should be possible to render
>> nodata with a color, we have to add support for it in GUI (set color)
>> and renderers. Currently there is no such support.
>>
>> Radim
>>
>>> Maybe there are other use cases as well.
>>>
>>> Regards,
>>> Marco
>>>
>>> Am 22.08.2012 17:49, schrieb Radim Blazek:
>>>>
>>>> Hi,
>>>> does anybody know why raster no data value is automatically added to
>>>> transparency list in properties dialog? It makes no sense IMO. No data
>>>> values are always rendered as transparent, no need to define them also
>>>> in transparent list.
>>>>
>>>> Radim
>>>> _______________________________________________
>>>> Qgis-developer mailing list
>>>> Qgis-developer at lists.osgeo.org
>>>> http://lists.osgeo.org/mailman/listinfo/qgis-developer
>>>
>>>
>>>
>>> --
>>> Dr. Marco Hugentobler
>>> Sourcepole -  Linux & Open Source Solutions
>>> Weberstrasse 5, CH-8004 Zürich, Switzerland
>>> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
>>> Technical Advisor QGIS Project Steering Committee
>>>
>>>
>>> _______________________________________________
>>> Qgis-developer mailing list
>>> Qgis-developer at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Weberstrasse 5, CH-8004 Zürich, Switzerland
> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee
>