[Qgis-user] Symbolizing a discrete or a boolean raster (Stéphane Henriod)

Wed Jan 11 10:59:20 PST 2017

I will share my opinion as I did in the developers list.

We users are as responsible for QGIS development as the developers. So
rather than asking what QGIS can do for us, maybe we should think what we
can do for QGIS. Don't just wait that a volunteer developer decide to spend
his free time developing a tool that you need.

IMHO, since it seems that you are not able/willing to sponsor the feature
yourself, sounds like a good opportunity for a small crowdfunding.

That way you would be able to contribute back to QGIS by giving your time
in finding a developer able to do it, setting up the crowdfunding,
advertise it, pay for part of it and so on.

It looks like a simple feature. It should not be very expensive (much less
than an ArcGIS license for sure), and if you think many people need this,
then the money will be easy to raise. And there is still time to introduce
this before QGIS 3.0.

Best regards,
Alexandre Neto

A qua, 11/01/2017, 14:55, Stéphane Henriod <s at henriod.info> escreveu:

> Thanks for checking, that's what I realized as well!
>
> Do you know if there is still a chance to include it for 3.0 or is it too
> late already?
>
> Cheers
>
> Stéphane
>
>
> Le mercredi 11 janvier 2017, DelazJ <delazj at gmail.com> a écrit :
>
> Hi Stéphane,
>
> I gave it a look and I'm sorry I was wrong. There have been some work on
> the raster classification but it was rather about color and extent
> management. See
> https://github.com/qgis/QGIS/pulls?utf8=%E2%9C%93&q=is%3Apr%20discrete%20is%3Aclosed%20
> or
> https://github.com/qgis/QGIS/pulls?utf8=%E2%9C%93&q=is%3Apr%20pseudocolor%20is%3Aclosed%20
> but testing upcoming 3.0 shows that nothing has changed in the area you are
> interested in.
>
> Harrissou
>
> 2017-01-11 4:37 GMT+01:00 Stéphane Henriod <s at henriod.info>:
>
> Hi Harrissou
>
> is there any description / documentation of the work that has been done on
> this (feature description, etc.)? If yes, I'd like to have a look and maybe
>
> Thanks a lot!
>
> Stéphane
>
>
> Le mardi 10 janvier 2017, DelazJ <delazj at gmail.com> a écrit :
>
> Hi Stéphane,
>
> 2017-01-10 4:02 GMT+01:00 Stéphane Henriod <s at henriod.info>:
>
> Hi Chris
> this is very nice! I indeed didn't know this trick and will certainly use
> it again in the future!
>
> However... :-)
>
> I am currently teaching QGIS to beginners and this for sure is not an
> appropriate method for them (especially in the case you have to generate
> the symbology file through a script)!
>
> Since the user can style continuous rasters with some "button-clicking", I
> believe the same option should be available for discrete rasters as well.
>
> I am thus wondering if anyone else than me sees it as a priority for QGIS?
> If yes, how to motivate the developers to take it for the next release and
> / or how much would such a development cost? (I unfortunately don't have
> the competences to do it myself)
>
> There have been some work done in the raster properties dialog in the
> upcoming 3.0. I don't know if your concern was covered though.
> If you want, you can move the question to the developer's list
> <http://qgis.org/en/site/getinvolved/mailinglists.html#qgis-developers-list>
> and discuss whether/how this can be implemented (and its requirements).
>
> Regards,
> Harrissou
>
> Thanks again and cheers!
>
> Stéphane
>
>
> Le mardi 10 janvier 2017, Chris House <housec01 at gmail.com> a écrit :
>
> Hi Stéphane,
>
> I don't know if this is what you are looking for or not but I have a
> method of classifying rasters by color based on a set (standard) colors.  I
> created a spreadsheet that has several required columns, value, red, green,
> blue...and you can have an optional field for a display value.  So say
> value 1 is water you can use that last column to name that value so that in
> the QGIS layer tree and in legend it says Water instead of value 1.
>
> save the spreadsheet as a csv and change the extension to .txt instead of
> .csv.
>
> I then go into the symbology section of the raster choose singleband
> pseudocolor. Use the folder to browse to your text file and click add.
> There is a format for this text file.  It is below.  If you need me to
> email it I will do that in direct email.
>
> # QGIS Generated Color Map Export File
> INTERPOLATION:EXACT
> -9999,0,0,0,255,NoData
> 0,176,176,176,255,Non-Forested
> 15,234,255,191,255,10 <=  CC < 20
> 25,187,230,149,255,20 <=  CC < 30
> 35,140,201,109,255,30 <=  CC < 40
> 45,98,176,74,255,40 <=  CC < 50
> 55,59,153,43,255,50 <= CC < 60
> 65,0,128,0,255,60 <=  CC < 70
> 75,15,92,11,255,70 <=  CC < 80
> 85,17,61,12,255,80 <=  CC < 90
> 95,16,36,12,255,90 <=  CC <= 100
>
> In my example if I don't assign a value it gets ignored by QGIS.  If you
> are wondering how to assign unique colors to say 200 unique values...just
> script it.  I have done this and as long as you have the number of unique
> values you want and to make them unique in the script it works.
>
> I hope this helps.  I know it isn't a "button" but to be honest I like
> this better.  If you already knew this...well then maybe it will help
> someone out in the future.
>
> --Chris
>
> On Mon, Jan 9, 2017 at 3:00 PM, <qgis-user-request at lists.osgeo.org> wrote:
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> Today's Topics:
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>    1. Re: Symbolizing a discrete or a boolean raster (Stéphane Henriod)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 9 Jan 2017 23:07:36 +0600
> From: Stéphane Henriod <s at henriod.info>
> To: Enrico Fiore <enricofiore at libero.it>
> Cc: qgis-user <qgis-user at lists.osgeo.org>
> Subject: Re: [Qgis-user] Symbolizing a discrete or a boolean raster
> Message-ID:
>         <
> CAK6pVBXURm_e7dRP+8SP9amPUUX0+Cn3GVxLPNjOHhno85o2rA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi
>
> thanks for following up!
>
> It actually does part of the job!
>
> Using *Color interpretation: Exact*, I can indeed input the exact values I
> want to display (1,5 and 10) and all other pixels are hidden.
>
> HOWEVER,
>
> this still feels like a workaround:
>
>    - In the case of a discrete raster with many (> 50) unique values, I do
>    not want to input all of them manually
>    - In some cases, I do not know in advance all the unique values of my
>    raster
>    - 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
>
> So I would say, we still need a render type "discrete raster" which offers
> the function to "retrieve all unique values" (and automatically apply a
> discrete color ramp)
>
> Attached a (fake) test dataset.
>
> Thanks and cheers
>
> Stéphane
>
>
> Le lundi 9 janvier 2017, Enrico Fiore <enricofiore at libero.it> a écrit :
>
> > Hi,
> > Sorry I can't do test, but if you use exact in color interpolation
> > parameter?
> >
> > Cheers
> >
> > Enrico
>
>
> Le lundi 9 janvier 2017, Stéphane Henriod <s at henriod.info> a écrit :
>
> > Hi
> >
> > unfortunately this is doing quite something different!
> >
> > If I have a raster with 10 Landcover classes (1,2,3,4,5,6,7,8,9,10) and I
> > want to display only 1,5 and 10, using *Discrete *(1: red, 5: yellow, 10:
> > blue) the following will happen:
> >
> > All pixels between 1 and 4 will be red
> > All pixels between 5 and 9 will be yellow
> > All pixels with 10 will be blue
> >
> > In this sense, the pixels are indeed not interpolated, but this still is
> > not the behavior I am expecting when styling discrete rasters.
> >
> > A "style discrete raster" function should offer the following:
> >
> >    - Automatically recover all unique values from the raster
> >    - Only display the pixels to which the user has explicitly assigned a
> >    color
> >
> > But thanks for your hint, this can be helpful in other cases!
> >
> > Cheers
> >
> > Stéphane
> >
> >
> > Le lundi 9 janvier 2017, Enrico Fiore <enricofiore at libero.it
> > <javascript:_e(%7B%7D,'cvml','enricofiore at libero.it');>> a écrit :
> >
> >> Hi,
> >> I think that the solution is in the QGIS documentation, that you can
> read
> >> here: http://docs.qgis.org/2.14/en/docs/user_manual/working_with_r
> >> aster/raster_properties.html#band-rendering
> >> you have to use *Singleband pseudocolor *and set color interpolation to
> >> Discrete.
> >>
> >> Enrico
> >>
> >>
> >> ----Messaggio originale----
> >> Da: "Stéphane Henriod" <s at henriod.info>
> >> Data: 09/01/2017 6.30
> >> A: "qgis-user"<qgis-user at lists.osgeo.org>
> >> Ogg: [Qgis-user] Symbolizing a discrete or a boolean raster
> >>
> >> Dear all
> >>
> >> As much as I love QGIS and use it in my everyday life, there is one
> >> feature that I find particularly annoying: the styling of discrete
> rasters.
> >>
> >> Basically, if I have a raster layer consisting of discrete landcover
> >> values (1: water, 2: forest, 3: built-up), it seems that there is no
> easy
> >> way to style it. QGIS will assume that the data is continuous and
> basically
> >> interpolate the color between each value, which leads to the following
> >> issues:
> >>
> >> Let's say I want to display only water and built-up (values 1 and 3),
> >> water in blue and built-up in grey. QGIS will still display the forests,
> >> using a color somewhere "between" blue and grey. My only left option is
> to
> >> process the raster to actually replace all the 2 with NoData, which is
> >> highly unpractical...
> >>
> >> Same if I have a boolean raster (only 0 and 1 values). QGIS will by
> >> default make a color ramp from 0 to 0.9999.
> >>
> >> Also, the whole rather feels like a work-around for a missing feature.
> >>
> >> I dream of a feature similar to this one from ArcGIS:
> >> http://resources.arcgis.com/en/help/main/10.1/index.
> >>
> html#/representing_unique_categories_such_as_land_use/009t00000074000000/
> >> where all unique values are styled independently and where I can easily
> >> skip the values I don't want to see on my map.
> >>
> >> I asked a question here:
> >> http://gis.stackexchange.com/questions/194116/qgis-style-a-d
> >> iscrete-raster
> >>
> >> and opened a ticket here:
> >> http://hub.qgis.org/issues/14845
> >>
> >> But none has gotten lots of attention yet... Am I the only one to be
> >> annoyed by this? If no, please raise your hand and let's try to get some
> >> momentum and see how to push this feature forward!
> >>
> >> Thanks a lot in advance!
> >>
> >> Cheers
> >>
> >> Stéphane
> >>
> >>
> >
>
> --
> Stéphane Henriod
> CIM-Expert for GIS and Green Economy Statistics
>
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> --
> Stéphane Henriod
> CIM-Expert for GIS and Green Economy Statistics
>
> Национальный статистический комитет Кыргызской Республики
> Кыргыз Республикасынын Улуттук статистика комитети
> National Statistical Committee of the Kyrgyz Republic
>
> 374 Фрунзе ул. / Frunze str.
> 720033 Бишкек / Bishkek
>
> T   +996 778 46 99 02 (KG)
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> E    s at henriod.info
> W   http://www.stat.kg
> W3W: nightfall.into.bucket
> <https://map.what3words.com/nightfall.into.bucket>  //  запас.союз.дружный
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> --
> Stéphane Henriod
> CIM-Expert for GIS and Green Economy Statistics
>
> Национальный статистический комитет Кыргызской Республики
> Кыргыз Республикасынын Улуттук статистика комитети
> National Statistical Committee of the Kyrgyz Republic
>
> 374 Фрунзе ул. / Frunze str.
> 720033 Бишкек / Bishkek
>
> T   +996 778 46 99 02 (KG)
> T   +49 176 280 11 050 <+49%20176%2028011050> (DE)
> E    s at henriod.info
> W   http://www.stat.kg
> W3W: nightfall.into.bucket
> <https://map.what3words.com/nightfall.into.bucket>  //  запас.союз.дружный
> <https://map.what3words.com/запас.союз.дружный>
>
>
>
>
>
> --
> Stéphane Henriod
> CIM-Expert for GIS and Green Economy Statistics
>
> Национальный статистический комитет Кыргызской Республики
> Кыргыз Республикасынын Улуттук статистика комитети
> National Statistical Committee of the Kyrgyz Republic
>
> 374 Фрунзе ул. / Frunze str.
> 720033 Бишкек / Bishkek
>
> T   +996 778 46 99 02 (KG)
> T   +49 176 280 11 050 (DE)
> E    s at henriod.info
> W   http://www.stat.kg
> W3W: nightfall.into.bucket
> <https://map.what3words.com/nightfall.into.bucket>  //  запас.союз.дружный
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-- 
Alexandre Neto
---------------------
@AlexNetoGeo
http://sigsemgrilhetas.wordpress.com
http://gisunchained.wordpress.com
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