[Qgis-user] buffer around random points

[Nicolas Cadieux]

Hi,

You can use a vector layer as suggested or use a raster layer with a specific value for land or water.  You can then use something like the point sampling tool plugin (a plugin that you must install and activate) to retrieve the value of the point on the raster of vector layer.  

Make sure your statistics works with spatial data.  Using a standard statistic with spatial data may give you bad results.  

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 14 avr. 2021 à 03:07, Raymond Nijssen <r.nijssen at terglobo.nl> a écrit :
> 
> Hi Milena,
> 
> There's an algorithm "Random Points in Polygons" that will only return points within the polygons of a layer. So you need a vector layer for land for the area you are interested in.
> 
> Hope this helps,
> Raymond
> 
>> On 14-04-2021 08:36, Milena Muehler wrote:
>> Dear community!
>> I’m new to QGIS and hope you can follow my process and my question. Would be more than happy to get your help!
>> So I have a raster layer with a cumulative value for each raster giving information about land modification (in 2016)
>> I have another vector layer with points providing information where an outbreak of a zoonotic infectious disease occurred (in 2016)
>> I want to examine the effect / association between  land modification and outbreak (I´ll do this with a binary logistic regression analysis in SPSS) therefore I want to generate a text file with values of the land modification for the location of the outbreak - I’ve done this with the tool "point sampling“.
>> But I also need values of land modification located at the points „no-outbreaks“. (to calculate the binary logistic regression analysis later in SPSS) Therefore I’ve generated random points. However, these points are truly random :)
>> So most random point „lay in the ocean“ and therefore I don’t get values of land modification.
>> So my question: How do I deal with that? Can I give a kind of command that all random points have to lie on land? and to give a certain radius for the „not random“ points - outbreaks.
>> someone said I can do this via raster calculator. But I cannot follow it, since I don’t calculate two raster layers?! I gave me this kinda command to deal with my issue: (via raster calculator?!)
>> L = grid cell is on land
>> B = Buffer around outbreaks with radius r (tbd: minimum distance between outbreaks and random non-outbreaks)
>> D = L / B (difference  "L without B „ = country on which a random non-outbreak can lay)
>> Thank you so much!!!!!!!
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