[Qgis-user] basic contouring and kriging

[Nicolas Cadieux]

Hi,

Krigging functions are part of the SAGA Algorithms.  If you do not see 
SAGA in the processing toolbox, then you probably need to activate the 
provider.  Activate the toolbox, go to the processing options (the 
wrench), Processing, Providers.  You may want to install the the 
Processing Saga Next Gen Provider plugin instead.

I don't know how they go from the tin to the raster.  I imagine they use 
the nearest neighbor.

Nicolas

On 2021-12-09 4:57 p.m., Firstname Lastname wrote:
> Thanks for the information above, it was very helpful and i now have a 
> better understanding of the interpolation process.
> As a follow up question, i could not find the krigging function in the 
> processing toolbox, only TIN and IDW.  where do i look for the 
> krigging interpolation
> Also, i understand the construction of delawney triangles and veronoi 
> diagrams now and how the veronoi cells are constructed.  What i am not 
> clear on is, once you have completed the interpolation and you have 
> your delawney triangle boundaries, how does this get translated to at 
> regular grid.
> the triangular mesh is irregular, how does this get referred to a 
> rectangular grid?  if you have a brief description, that is adequate.
>
>
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>
> On Mon, Dec 6, 2021 at 2:51 PM Nicolas Cadieux 
> <njacadieux.gitlab at gmail.com> wrote:
>
>     Hi,
>
>     Open the Processing toolbox panel, search for 'Krigging'.  You
>     will see multiple SAGA modules. If you search for "interpolation",
>     you will find IDW AND TIN under Q modules and other methods under
>     the SAGA module. If you search for "grid" you will find multiple
>     algorithms under GDAL/Raster analysis.  See
>     https://gdal.org/tutorials/gdal_grid_tut.html#gdal-grid-tut and
>     https://gdal.org/programs/gdal_grid.html for other methods. This
>     should cover it.
>
>     The idea is generally to interpolate a raster surface from points
>     or lines containing a z field or a z value (in 3D files).  After,
>     you use Raster/Extract/Contour on this new raster layer.  You can
>     also install the contour plugin.  That uses a point file only but
>     I don't know the what algorithm it uses.
>
>     You may find more algorithm using CrimeStat or GeoDa softwares.
>
>     Hope this helps.
>
>
>     Nicolas
>
>
>
>     On 2021-12-06 1:59 p.m., Firstname Lastname wrote:
>>     hello group:
>>     i want to demonstrate some of the pitfalls of computer contouring
>>     methods with limited datasets.  i wanted to use a small dataset
>>     to demonstrate several contouring algorithms.  In particular,
>>     linear interpolation, inverse weighted, nearest neighbour and
>>     kriging.  Are any of these built into QGIS?  i do not see any
>>     options to control the contouring in the plugins for any options
>>     other than the default.
>>     thank you if you can provide any help.
>>
>>     -- 
>>     Byron Veilleux, MSc. P.Geo
>>     Conjugate Geologic Services Limited
>>     Calgary, Alberta Canada
>>     byron at conjugategeo.com
>>     Cell:4037108414
>>
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>
>     -- 
>     Nicolas Cadieux
>     https://gitlab.com/njacadieux
>
-- 
Nicolas Cadieux
https://gitlab.com/njacadieux
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