[Qgis-user] Raster to Vector without losing the symbology

[Nicolas Cadieux]

Hi,

I looked at your problem.  Indeed, using the Group Stat plugin, you will 
not be able to easily identify which polygon has the highest values.  
You can export a csv with the cross tabulation results but there is 
still no way to know which Polygon with the value A has highest value.

You can create a new field called "max" using the following expression.

maximum("Area",group_by:="Polygon")

That will giving you the highest value for each group.  Then, you can 
select polygon using the following expression

"Area" = "max"

Nicolas


On 2021-07-18 3:08 p.m., Nicolas Cadieux wrote:
> Use the extract value by location to get the values from the point 
> back into the vector grid…
>
> Nicolas Cadieux
> https://gitlab.com/njacadieux <https://gitlab.com/njacadieux>
>
>> Le 18 juill. 2021 à 15:06, Nicolas Cadieux 
>> <njacadieux.gitlab at gmail.com> a écrit :
>>
>> 
>> Hi,
>>
>> Another way is to create a vector grid with the same size and pixel 
>> posting as the original.  Then, get the centroids and use the point 
>> value tool to get the band values… This will give you a vector file 
>> but the file will be heavy. You could merge the vector grids after to 
>> merge values with similar values….
>>
>> Ask yourself if you really need a vector file first.  This is not 
>> always the best file format for you data.
>>
>> Nicolas Cadieux
>> https://gitlab.com/njacadieux <https://gitlab.com/njacadieux>
>>
>>> Le 18 juill. 2021 à 14:56, Nicolas Cadieux 
>>> <njacadieux.gitlab at gmail.com> a écrit :
>>>
>>>  Hi,
>>> You could create a style that could apply to both raster and vector 
>>> layers but that would not help much here.  The problem is that you 
>>> need to create the vector based on one of the raster Bands and not 
>>> all three.  One way could be to combine all three fields into one. 
>>>  If your RGB is 155 025 255, make this a raster band with 155025255. 
>>> Then, I guess you could use that 4th band to make the vector layer, 
>>> then resplit the data into 3 fields and use that to create the 
>>> colour profile.
>>>
>>> Nicolas Cadieux
>>> https://gitlab.com/njacadieux <https://gitlab.com/njacadieux>
>>>
>>>> Le 18 juill. 2021 à 12:51, krishna Ayyala <ayyalakrishna at gmail.com> 
>>>> a écrit :
>>>>
>>>> 
>>>> I have an image on my qgis map that has 3 bands. Band1 (red), 
>>>> Band2(green) and Band3(blue). This image has different colors.Is it 
>>>> possible to convert this image into a vector which should look 
>>>> exactly like the image.
>>>>
>>>> That means; Is it possible to have the vector file that should have 
>>>> the same colors as that of the image.
>>>>
>>>> Regards.
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-- 
Nicolas Cadieux
https://gitlab.com/njacadieux

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