[GRASS-user] v.kernel - Points weighted with attribute ?

[Taïs]

Hi Micha,


I successfully run your R script. However to output is weird and I don't 
know how to fix it.

In v.kernel, you can setup the "raduis" parameter to control what I 
assume to be the size of the kernel (of the moving window). I made one 
test with radius=300 and another with value 3000. The result of the 
first is more what I would expect in terms of spatial variability.


When I try your script, the output raster has a size of 128x128 which 
did not correspond at all to my computational region, and thus the 
resolution is not the same as the one defined in the computational region.


The other thing is that I'm wondering if it is possible to control the 
size of the moving window with the "density" function in R. I already 
tried the 'n' parameter but it doesn't change anything..


I also tried with real weights (the number of inhabitants) and a unity 
weighting (value 1 for all points) to see it there is a change and there 
is which proof the weights affect the output :)


Le 22/10/19 à 13:41, Micha Silver a écrit :
>
> Here is the script.
>
> Let me know how it goes. (I might try to take time to make it into a 
> GRASS addon)
>
>
> On 10/22/19 2:33 PM, Taïs wrote:
>>
>> Hi Micha, thanks for your repply.
>>
>>
>> For my own need, I think your solution is enough and I would like to 
>> try if you agree to send the R script.
>>
>>
>>
>> Le 22/10/19 à 12:53, Micha Silver a écrit :
>>>
>>> On 10/21/19 1:33 PM, Tais wrote:
>>>> Hi all,
>>>>
>>>> I would like to compute a raster density map ("heat map") from 
>>>> vector points using v.kernel. The points represent house addresses. 
>>>> However, I would need to weight the points with a value stored in 
>>>> the attribute table (number of inhabitants). I saw on the module 
>>>> manual page that this functionality is a "known issue".
>>>>
>>>> I imagined a solution to by-passe the limitation: duplicate each 
>>>> point as many time as needed (according to the value stored in the 
>>>> attribute table) and use this new layer directly in v.kernel. 
>>>> However, I think it will definitely not be the most efficient way 
>>>> to do the trick. Do you have an alternative in mind ?
>>>>
>>>> Of course the best solution would be that someone in the 
>>>> development community would have the time and the kindness to 
>>>> implement this function directly in the module (I'm not skilled in 
>>>> C and thus cannot try myself).
>>>>
>>>
>>> Maybe not the answer you are looking for, but you can create a 
>>> weighted kernel density in R. I can send an R script that is 
>>> intended to be run from within a GRASS session. It accepts a point 
>>> vector and attrib column, and creates a kernel density raster, 
>>> weighted by the attribute values (using the R defaults for bandwidth 
>>> and Gaussian kernel)
>>>
>>> Requires, of course, that R is installed, with the packages: 
>>> spatstat, raster, rgrass7.
>>>
>>>
>>>> NB: Sorry if I should have posted this on the developer mailing 
>>>> list. I hesitated but decided to post here finally.
>>>>
>>>> Best,
>>>>
>>> -- 
>>> Micha Silver
>>> Ben Gurion Univ.
>>> Sde Boker, Remote Sensing Lab
>>> cell: +972-523-665918
> -- 
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
-------------- section suivante --------------
Une pièce jointe HTML a été nettoyée...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20191025/042e671e/attachment-0001.html>
-------------- section suivante --------------
Une pièce jointe autre que texte a été nettoyée...
Nom: Micha_Rscript_unity_weighted.png
Type: image/png
Taille: 19177 octets
Desc: non disponible
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20191025/042e671e/attachment-0004.png>
-------------- section suivante --------------
Une pièce jointe autre que texte a été nettoyée...
Nom: Micha_Rscript_population_weighted.png
Type: image/png
Taille: 18170 octets
Desc: non disponible
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20191025/042e671e/attachment-0005.png>
-------------- section suivante --------------
Une pièce jointe autre que texte a été nettoyée...
Nom: vkernel_radius_3000.png
Type: image/png
Taille: 75272 octets
Desc: non disponible
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20191025/042e671e/attachment-0006.png>
-------------- section suivante --------------
Une pièce jointe autre que texte a été nettoyée...
Nom: vkernel_radius_300.png
Type: image/png
Taille: 95623 octets
Desc: non disponible
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20191025/042e671e/attachment-0007.png>
-------------- section suivante --------------
Une pièce jointe autre que texte a été nettoyée...
Nom: tgrippa.vcf
Type: text/x-vcard
Taille: 4 octets
Desc: non disponible
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20191025/042e671e/attachment-0001.vcf>