[Qgis-user] Vacuuming a vector polygon layer with a point layer in QGIS 2.8.2 (windows)

[Bernd Vogelgesang]

I think the aim is exactly that, to FIND the radius for each biogas plant  
which is able to provide the plant with enough resources.

I once had a quite similar problem, to create new polygons which had to  
reach a certain sum value of credits per unit, but overlaying other  
polygons with different credit values.

My semi-optimal solution was to "rasterize" the polygons to a vector grid.
I then selected the grid cells and used a statistics plugin to sum up the  
credits until I reached the desired amount, and then saved the selection  
as a new feature. The Live Statistics plugin could be used for that.

It really depends on how many plant points you already have. If they are  
many, this will be a tedious and boring job and you better might find  
someone to code a little python script.

If I had the abilities, I would code something like this:

Rasterize your polygons to a vector grid with your gas potential value (so  
if grid size is hectares, then simply your value)
Iterate over your point layer:
x = plant gas consuption
select cell underneath point 1
y = cell gas potential

set cell value to 0 (your "vacuum")
select next cells circularily around the first and add cells values to y
until y >= x
copy selected cells, dissolve them and save as a new feature in a new layer

next point


Once wanted to code sth like this in R, but I'm sure there are many people  
with PYQGIS-abilities who could do sth like this easily.
Could maybe even better work with real raster ... no idea.

Cheers
Bernd


Am 03.07.2015, 14:45 Uhr, schrieb Kristian Evers <kreve at gst.dk>:

>
> Hi Julie.
>
>
> You need to define a surrounding area for each of the biogas plants. I  
> suggest you base the >surrounding areas on the polygons you already  
> have, so that each plant has a polygon that is a union >of several  
> surrounding biogas-potential polygons. How to do this is up to you.
> Hereafter you can select all potential-polygons that intersect the  
> plant-polygons and sum up the >potentials within each of the   
> plant-polygons.
>
>
> I hope that was enough to bring you on the right track.
>
>
> Kristian
>
>
>
> Fra: qgis-user-bounces at lists.osgeo.org  
> [mailto:qgis-user-bounces at lists.osgeo.org] På vegne af Julie Houge Hansen
> Sendt: fredag 03. juli 2015 13:35
> Til: qgis-user at lists.osgeo.org
> Emne: [Qgis-user] Vacuuming a vector polygon layer with a point layer in  
> QGIS 2.8.2 (windows)
>
>
> Dear all
>
>
> I have tried asking my local QGIS expert but unfortunately she is for  
> once not able to help me. I >hope someone can.
>
>
> -          I have a vector polygon layer that contains data for the  
> amount of biogas potentially available >in a polygon  - unit is  
> m3/ha/year. The polygons are of varying size.
> -          I have another vector point layer with data for the amount of  
> biogas already produced on >specific biogas plants – unit in m3/year.
> -          I would like to combine the two layers so that I “vacuum” the  
> area surrounding the biogas >plants for biogas potential. This will  
> reveal where there are still areas with sufficient >biomass available  
> for a new biogas plant to be build.
>
> I have no clue how to do this calculation but I think it should be  
> possible. Can anyone help me out?
>
>
> The overview I have of my data now looks like this:
>
>
>
> The size of the shown point data is independent on the polygon layer. I  
> would like it to be dependent >on the biogas potential available (in the  
> polygon layer). I would like the size of the points to >reflect how far  
> you would have to drive (radius to the biogas plant) in order to get all  
> the biomass >needed to produce the biogas you intend to.
>
> I am using QGIS version 2.8.2 64 bit with Windows.
>
> Best regards
>
> Julie Houge Hansen
> PhD Student, Inst. of Chemical Eng., Biotechnology and Environmental  
> Tech.>	>

>> Tlf.	
>> +4565507212

>> Email	
>> juhh at kbm.sdu.dk

>> Addr.	
>> Niels Bohrs Allé 1, DK-5230 Odense M, Denmark

>
>>
>

>
> Campusvej 55 · 5230 Odense M · Tlf. 6550 1000 · www.sdu.dk
>
>
>



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