[SOLVED] Turning Band Simulation Problem

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[SOLVED] Turning Band Simulation Problem

Postby niafall » Fri Nov 04, 2016 7:56 pm

I am using the turning band simulation function, simtub, to perform conditional geostatistical simulations as follows:

- Fit a variogram model to the experimental variogram calculated from bottom trawl density data using the model.auto function:
Code: Select all
model.vario.Y.15 <- model.auto(vario.Y.15, struc=melem.name(c(1,2)), draw=T)

- Initiate a grid and neighbourhood
Code: Select all
grid.simu <- db.grid.init(poly.data,nodes=c(gnx,gny))
neigh.simu <- neigh.init(ndim=2,type=2,nmini=5,nmaxi=100,dmax=60)

- Simulate across the grid
Code: Select all
grid.simu <- simtub(dbin=db.data.trans, dbout=grid.simu, model=model.vario.Y.15,
                    neigh=neigh.simu, uc="", mean=0, seed=1337, nbsimu=ns,
                    nbtuba=1000, radix="Simu", modify.target=TRUE)

In most cases the entire grid (which is based on an outline polygon of the area of interest) is filled with simulated values. In some cases though, the grid does not fill and the extent of the simulated surface appears to be limited to some of the data points.

Is this related to the amount of data points, the variograms properties, or the simulation itself?
Posts: 12
Joined: Tue May 17, 2016 5:46 pm

Re: Turning Band Simulation Problem

Postby Didier Renard » Fri Nov 04, 2016 11:23 pm

Difficult to say without any data nor display.

It is more probably used to the neighborhood used for conditional kriging.
Its dimension is set to 60, which means that conditioning data will not be looked for outside a circle with radius 60 centered on each target grid node.
If not enough data (nmini=5) is found within this circle, the conditional kriging cannot be performed.

Then we could have imagined to place a non-conditional simulation instead of the conditional one (which is impossible to obtain). But we have selected not to produce any resulting value ... so as to ask the user to wonder why this has happened.

And this works fine obviously :)

Let me know if this helps.
Didier Renard
Posts: 240
Joined: Thu Sep 20, 2012 4:22 pm

Re: Turning Band Simulation Problem

Postby niafall » Fri Nov 11, 2016 3:33 pm

Hi Didier,

You were correct in that the neighbourhood settings would not allow for the grid to fill, given the distribution of the hauls in space.

This has been overcome simply by adjusting the neighbourhood. :)

Many thanks.
Posts: 12
Joined: Tue May 17, 2016 5:46 pm

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