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

[Julie Houge Hansen]

I think this solution sounds great but I'm afraid I'm much too green using QGIS to know how to do it. When downloading QGIS I got the GRASS GIS 6.4.3 GUI and command line as well but I have never used it and don't know how to. I don't even know how to open the vector files in the GRASS program...

Is it possible to get a more precise description of what to do?

Best regards

Julie Houge Hansen
PhD Student, Inst. of Chemical Eng., Biotechnology and Environmental Tech.

Tlf.

+4565507212<tel:+4565507212>

Email

juhh at kbm.sdu.dk<mailto:juhh at kbm.sdu.dk>

Addr.

Niels Bohrs Allé 1, DK-5230 Odense M, Denmark


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Fra: Micha Silver [mailto:micha at arava.co.il]
Sendt: 3. juli 2015 15:27
Til: Julie Houge Hansen; qgis-user at lists.osgeo.org
Emne: Re: [Qgis-user] Vacuuming a vector polygon layer with a point layer in QGIS 2.8.2 (windows)

I think you can solve this problem nicely by moving everything to rasters. There is the concept of a "cost" raster that totals how difficult it is to go from a certain start point to anywhere else in the region. In your case, instead of total "difficulty" you would total potential biomass. You would create a raster showing the total biomass "collected" by starting at each biogas plant.

This could be done with the GRASS module r.cost.  See [1].
Your polygon layer of biogas potential would be imported into GRASS, then converted to a raster (v.to.rast). You would also import the point layer of plants into GRASS as a point vector. Then run the module with the biogas potential as the input parameter, and the plants as the "start_points". And you would set a value for the "max_cost" parameter which would be the maximum biomass any plants needs. Again, the output raster would represent the total amount of biomass accumulated when starting from any of the plants.

Hope that helps


[1]  http://grass.osgeo.org/grass70/manuals/r.cost.html
On 07/03/2015 02:35 PM, Julie Houge Hansen wrote:
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:
[cid:image002.jpg at 01D0B7EA.ECF083C0]

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<tel:+4565507212>

Email

juhh at kbm.sdu.dk<mailto:juhh at kbm.sdu.dk>

Addr.

Niels Bohrs Allé 1, DK-5230 Odense M, Denmark


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________________________________

Campusvej 55 · 5230 Odense M · Tlf. 6550 1000 · www.sdu.dk<https://webmail.sdu.dk/owa/redir.aspx?C=866ea63d2ed24495a0928ea339532b2a&URL=http%3a%2f%2fwww.sdu.dk%2f>




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