Delft 3D FM Interpolation methods  Delwaq  Delft3D
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Delft 3D FM Interpolation methods
Andrea Neri, modified 4 Years ago.
Delft 3D FM Interpolation methods
Youngling Posts: 1 Join Date: 7/21/16 Recent PostsI am trying to understand how the interpolation of the computational grid works and the differences between different grid interpolation methods.
I have a DEM file which has a resolution of 30 meters. Therefore the xyz file that I import in the software as "bed level" has the same resolution (30m).
My computation grid is a combination of a rectangular grid and a triangular grid, as shown in the attached picture (islands_scale.png), and the length of the edge of one triangle ranges from 400m to 600m.
The software allows to use these Interpolations methods:
1) Triangulation Interpolation
2) Averaging
Averaging can be assessed in these ways:
1) Simple average
2) Closest point
3) Maximum value
4) Minimum value
5) Inverse weighted distance average
6) MinAbs
7) KdTree
and gives the possibility to choose the minimum number of points which the average is based on and also the size of the search volume: 1.0 is the "actual cell" and 1.5 is 50% more than the "actual cell" in all direction.
The first strange behaviour I notice is that regardless the Averaging method I use (I didn't try MinAbs and KdTree), I obtain the same interpolated grid, meaning that all the nodes have the same elevation value. [I don't notice changes even if (using the same Averaging method) I increase the minimum number of sample points to be taken into account to compute the average. I notice changes (between the same Averaging method) only between a search cell size value equal to 1.0 and a search cell size value equal to 1.5.]
So my first question is: Why the values of the elevation for each node are not changing according to the Averaging method?
If I use the Triangulation Interpolation, then I obtain an interpolated grid with different elevations compared to the grids obtained with the Averaging methods. I read on the user manual that the Triangulation Interpolation "performs a Delauney triangulation on the sample point set before projecting onto the grid".
Second question: How does exaclty the Triangulation Interpolation method work in this case? (I know what a triangulation inerpolation is but I can't understand how it is applied on a xyz file which has equally distributed points and how this triangulation is used to caculate the elevation of the nodes of the computational grid)
Third question: What is the "actual cell" that works as search volume needed to compute the average of sample points?
Please if I was not clear contact me at Andrea.Neri@deltares.nl or andreaneri.91@gmail.com
Best Regards,
Andrea