[R-sig-Geo] GRTS sampling - 2-level design

[Roger Bivand]

On Thu, 7 Oct 2021, John Wilson wrote:

> Oh, sorry - I normally use the grts() function from the spsurvey package.
> My hacky approach was to make 10 balanced points with grts(), followed by
> imposing a 5 km buffer around each one, and either systematic sampling
> within the buffer circle, or running a separate GRTS for the 5 points
> within each 5 km buffer circle. Even writing this makes me cringe though,
> so hoping for something legitimate... I'll contact the authors if I don't
> get any solid leads on here.

That makes sense. Perhaps comparison with the implementation in SDraw 
might be of interest. Please report back on progress (or no progress), 
someone else may well face the same problem. By the way, Task Views are 
being "re-booted", and it seems clear that a section on spatial sampling 
in one or several task views (Spatial, Environmetrics) would be helpful if 
someone could author one. For Spatial, a PR to 
https://github.com/r-spatial/task_views (we will be converting to markdown 
rather than ctv XML markup soon).

Roger

>
> On Thu, Oct 7, 2021 at 10:40 AM Roger Bivand <Roger.Bivand using nhh.no> wrote:
>
>> On Thu, 7 Oct 2021, John Wilson wrote:
>>
>>> Hi everyone,
>>>
>>> I'm working on a sampling design using GRTS, but I'm running into a
>>> logistics problem. The field crew can set 5 nets per day, but only
>> within a
>>> 5 km stretch, due to travel time constraints. With 10 sampling days,
>> that's
>>> a total of 50 sites. The overall sampling area is huge, so running a
>>> regular GRTS design for 50 sites results, of course, in much larger
>>> distances between sampling points.
>>>
>>> Is there a legitimate way to create a 2-level GRTS design, where in step
>> 1
>>> we choose 10 spatially-balanced sampling points (one "core" point per
>>> sampling day), and then for each of these "core points", we create a grid
>>> of 5 sampling points that are constrained to all be within 5 km from each
>>> other? I can make that happen code-wise, but am not sure what the
>>> implications on spatial balance are, or if there's a built-in way to do
>>> this.
>>
>> Do you have a code example? Are you using BalancedSampling, SDraw or
>> Spbsampling or packages (probably SDraw)? Have you run any simulations to
>> try to get a first assessment on the impact of constraining your sample?
>> Might approach a package author also help?
>>
>> Roger
>>
>>
>>>
>>> Would appreciate any thoughts...
>>> John
>>>
>>>       [[alternative HTML version deleted]]
>>>
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>>
>> --
>> Roger Bivand
>> Emeritus Professor
>> Department of Economics, Norwegian School of Economics,
>> Postboks 3490 Ytre Sandviken, 5045 Bergen, Norway.
>> e-mail: Roger.Bivand using nhh.no
>> https://orcid.org/0000-0003-2392-6140
>> https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
>>
>

-- 
Roger Bivand
Emeritus Professor
Department of Economics, Norwegian School of Economics,
Postboks 3490 Ytre Sandviken, 5045 Bergen, Norway.
e-mail: Roger.Bivand using nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en