[Qgis-developer] Symbolizing a discrete or a boolean raster

[Stéphane Henriod]

Hi

let me move here a request that has been shortly discussed on the
user-mailing list:
http://lists.osgeo.org/pipermail/qgis-user/2017-January/038793.html
http://lists.osgeo.org/pipermail/qgis-user/2017-January/038795.html
http://lists.osgeo.org/pipermail/qgis-user/2017-January/038801.html

and for which a ticket is open:
http://hub.qgis.org/issues/14845

I was said that some work has been done in this direction for 3.0 but I
don't know if it completely covers the feature request

----------------------

When styling a discrete or boolean raster, there seems to be no direct
method, only a few workarounds. The feature I dream of would do the
following:

   - A new render type "Discrete raster"
   - One button allows to fetch all unique values form the raster (with a
   warning message if there are more than XXX unique values)
   - A color ramp is applied by default
   - I can multi-select values and apply them the same style and / or the
   same label
   - I can remove values. The pixels with those values will simply not be
   displayed
   - I can save my color map and load an existing color map

So pretty much like the ArcGIS implementation:
http://resources.arcgis.com/en/help/main/10.1/index.html#/representing_unique_categories_such_as_land_use/009t00000074000000/

The current limitations I see (in 2.14):

   - The discrete values must be entered manually, which is a pain for a
   raster with many unique values (or if I don't know in advance what all
   values are)
   - If I click on *Classify*, QGIS will choose X values (based on the
   number of classes and the classification method (continuous or equal
   interval)), which no longer match the "exact" values of my raster. It
   doesn't really make sense to classify a discrete rendering
   - Although it is currently possible to style discrete rasters, the
   procedure is not really intuitive for beginners

----------------------

Is this a feature that is envisioned for 3.0? Is there anything I can do to
support it? (except coding it myself, since I don't have the skills for
that...)

Thanks a lot in advance

Cheers

Stéphane


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