Hi Stéphane,
2017-01-10 4:02 GMT+01:00 Stéphane Henriod <[email protected]
<mailto:[email protected]>>:
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 <[email protected]
<mailto:[email protected]>> 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,
<[email protected]> 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 <[email protected]>
To: Enrico Fiore <[email protected]>
Cc: qgis-user <[email protected]>
Subject: Re: [Qgis-user] Symbolizing a discrete or a
boolean raster
Message-ID:
<cak6pvbxurm_e7drp+8sp9ampuux0+cn3gvxlpnjohhno85o...@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
<[email protected]> 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 <[email protected]>
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 <[email protected]
> <javascript:_e(%7B%7D,'cvml','[email protected]');>>
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
<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" <[email protected]>
>> Data: 09/01/2017 6.30
>> A: "qgis-user"<[email protected]>
>> 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
<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
<http://gis.stackexchange.com/questions/194116/qgis-style-a-d>
>> iscrete-raster
>>
>> and opened a ticket here:
>> http://hub.qgis.org/issues/14845
<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
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Национальный статистический комитет Кыргызской Республики
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