Hi Ben, You are right, these mass-preserving splines are for continuous data - it seems I have been carried away from the original scope of the project while writing my email :)
Cheers, P 2013/6/27 Benjamin Ducke <[email protected]>: > On 06/26/2013 06:48 PM, Pierre Roudier wrote: >> >> Hi all, >> >> >>> This is an excellent point. While I like the mention of AQP in this >>> context, >>> I totally support a GRASS-based implementation with as few dependencies >>> as >>> possible. >> >> >> +1 - I think a native GRASS implementation would make a lot of sense. >> >>>> Yes, the thought of such "waffel voxels" is not exactly appealing. >>>> However, they may be a smaller problem in practice, since the voxel >>>> models themselves are often used to derive vertical slices >>>> ("profiles"), and those might look perfectly fine, even if derived >>>> from malformed voxels. GRASS does allow for individual X, Y and Z >>>> dimensions of voxels, so there is no technical problem with this. >>>> The results of the interpolation don't need to be beautiful, they >>>> just need to be as accurate and as true to the data as possible. >>>> >> >> That's the very nature of soils data - we soil scientists often deal >> with pixels of 10 to 500m resolution, to observe processes that occur >> generally in the first meter in the z axis! It is not a problem, and >> the challenge is to come up with tools that allow us to store, query >> and interpolate such data. >> >>> This is a popular topic in the soils literature-- vertical anisotropy can >>> be >>> an order of magnitude greater than what is found in the horizontal. >>> Restricted cubic splines have some desirable characteristics for dealing >>> with this kind of data-- however, these work best in the context of a >>> regression model. Also, there are the mass-preserving splines that are >>> more >>> useful in the "interpolation along the soil profile" sense. For >>> categorical >>> data, I would recommend the ordinal-ratio logistic regression model, >>> which >>> generates class-wise probability estimates. I have found this quite >>> useful >>> for generating probability depth-functions for categorical soil >>> properties. >>> I can elaborate as needed. >> >> >> The mass-preserving splines has become a key tool in the GlobalSoilMap >> project. An implementation in R exists but is not very efficient. This >> could be an opportunity to come up with a reference implementation! As >> mentioned by Dylan, various interpolation methods are available, >> restricted cubic splines look good as well. >> > > But is that method suitable for categorized input data? > Or does it only work for continuous soil properties? > A spline-based interpolator from 3D vector to 3D raster > already exists in GRASS (v.vol.rst). > > Best, > > Ben > >> >> Cheers, >> >> P >> > > > > -- > Dr. Benjamin Ducke, M.A. > {*} Geospatial Consultant > {*} GIS Developer > > [email protected] > _______________________________________________ > grass-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-dev -- Scientist Landcare Research, New Zealand _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
