Questions about pathdistGen() and ipdwInterp()

[dempsey-CMAR]

Hello,

I am planning to use your package to interpolate values from oceanographic sensors stationed around the coast of Nova Scotia.

I have looked through the functions in some detail and have a couple of questions :

1. How did you decide on the values of ipdw_range and ipdw_dist in pathdistGen()?
   I am particularly interested in why you chose the second break of the costfurf histogram for the first row of sf_ob (line 58).
   I am curious because I get different values of ipdw_dist depending on the order of sf_ob.

2. Also in regard to pathdistGen(): I think I followed most of the reclassifying, but why did you need to scale `costsurf_reclass' (line 74): costsurf_scaled <- ((ipdw_range / costsurf_reclass)^2)?

3. Finally, I am running into an issue where the contribution from some stations is 0 for the whole area (i.e., the raster layer output from ipdwInterp.R() is zero for every cell), despite the station being connected via water to the whole coast. I am trying to figure this out and will post a reprex if it doesn't get resolved, but let me know if this is a common/known issue.

Thanks!

[jsta]

I'm happy you're finding this code to be useful. It's been some years since I was seriously using this code myself so here's my best guess/recollection.

1. I recommend setting ipdw_range to a multiple of the distance among observation points. In the vignette I set it to 10x this value but I think it depends on what kind of spatial density you have in your observations. Try a few and see how it looks (you could also try a few in a leave-one-out cross validation scheme). I chose the second break for ipdw_dist because the first would be 0. Do you see a need to have this be set by the user instead of hard-coded?
2. I think this was ported from the reference code in Suominen et al. 2010 and I believe it's to enforce realistic spatial decay in a simple way without being overly complicated.
3. I don't recall this being an issue. My initial guess is that it's a spatial duplicate with one of your other points or that its distance with another point is smaller that the resolution of your raster inputs/outputs/intermediates.

P.S. I don't know if you're a Python user but even if you're not it might be a good idea to take a look at the following Python implementation in case it's useful to read through:
https://github.com/wrightky/ipdw

[dempsey-CMAR]

Thanks for the responses! I am just returning from vacation today, but will take a closer look this week and then close the comment.