[Qgis-user] Symbolizing a discrete or a boolean raster (Stéphane Henriod)
Stéphane Henriod
s at henriod.info
Mon Jan 9 19:02:17 PST 2017
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)
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
> <javascript:_e(%7B%7D,'cvml','qgis-user-request at lists.osgeo.org');>>
> wrote:
>
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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
>> <javascript:_e(%7B%7D,'cvml','s at henriod.info');>>
>> To: Enrico Fiore <enricofiore at libero.it
>> <javascript:_e(%7B%7D,'cvml','enricofiore at libero.it');>>
>> Cc: qgis-user <qgis-user at lists.osgeo.org
>> <javascript:_e(%7B%7D,'cvml','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.gm
>> ail.com
>> <javascript:_e(%7B%7D,'cvml','CAK6pVBXURm_e7dRP%2B8SP9amPUUX0%2BCn3GVxLPNjOHhno85o2rA 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
>> <javascript:_e(%7B%7D,'cvml','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
>> <javascript:_e(%7B%7D,'cvml','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');>
>> > <javascript:_e(%7B%7D,'cvml','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
>> <javascript:_e(%7B%7D,'cvml','s at henriod.info');>>
>> >> Data: 09/01/2017 6.30
>> >> A: "qgis-user"<qgis-user at lists.osgeo.org
>> <javascript:_e(%7B%7D,'cvml','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/009t00
>> 000074000000/
>> >> 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)
T +49 176 280 11 050 (DE)
E s at henriod.info
W http://www.stat.kg
W3W: nightfall.into.bucket
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