[Qgis-user] Symbolizing a discrete or a boolean raster (Stéphane Henriod)
DelazJ
delazj at gmail.com
Tue Jan 10 01:49:19 PST 2017
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:
>>>
>>> 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.gm
>>> ail.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/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.
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> T +49 176 280 11 050 <+49%20176%2028011050> (DE)
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