- Dear list,

Just a simple question...

I'm trying to produce a contour map from a structural surface. This

surface is highly non-stationary (actuaally dips towards NW)

I wolud like to know which could be the best solution for getting a

reliabel map:

1) Fit a plyonomial surface to the sample values, which is used as a

drift. Substract the drift from the observations to get the residuals.

Estimate the variogram of the residuals (now the residual variable is

stationary). Perform OK on the residuals. Add the polynomial surface to

the residuals to get the interpolated surface.

2) Compute variograms from the observations. Use universal kriging to

get the interpolated surface.

Thank you

Oriol

--

______________________________________

Oriol Falivene

ofaliven@...

http://www.ub.es/ggac

tel. (+34) 93 4021373

fax (+34) 93 4021340

Fac. de Geologia,

Univ. de Barcelona - Dear Oriol Falivene,

If you could assume a linear (or polynomial trend) for the dip, the situation

you are talking about, is the classical situation for the use of intrinsic

random functions, IRKk-kriging and generalized covariances or generalized

variograms. The theory is quite good explained in the thick standard books

on Geostatistics such as that of Cressie or of Chiles and Delfiner. In

pratice it is quite difficult to actually estimate the generalized variograms

and to find good software for that.

Can anyone hint me and Oriol to good software for IRK-k kriging, especially

regarding the estimation and modelling of the generalised variograms? The

IRKk/Universal kriging is present everywhere, but the modelling...?

In case of nonpolynomial trend, the estimation of the variogram gets even more

tricky.> I wolud like to know which could be the best solution for getting a

1) is wrong, since removing the trend removes the assumption of stationarity,

> reliabel map:

> 1) Fit a plyonomial surface to the sample values, which is used as a

> ...

which often also results in strange behavior of the variogram (e.g. dropping

for long distances again)

2) is not strictly wrong, however whenever a trend is really present, you can

not fit a ordinary variogram model, due to a quadratic increase in the

variogramm. You will need a generalized variogram model and than we are back

at IRFk-kriging.

Best regards,

Gerald v.d. Boogaart

Am Donnerstag, 5. Januar 2006 10:57 schrieb Oriol Falivene:> Dear list,

--

>

> Just a simple question...

>

> I'm trying to produce a contour map from a structural surface. This

> surface is highly non-stationary (actuaally dips towards NW)

> I wolud like to know which could be the best solution for getting a

> reliabel map:

>

> 1) Fit a plyonomial surface to the sample values, which is used as a

> drift. Substract the drift from the observations to get the residuals.

> Estimate the variogram of the residuals (now the residual variable is

> stationary). Perform OK on the residuals. Add the polynomial surface to

> the residuals to get the interpolated surface.

>

> 2) Compute variograms from the observations. Use universal kriging to

> get the interpolated surface.

>

> Thank you

>

> Oriol

> --

>

>

>

> ______________________________________

>

> Oriol Falivene

> ofaliven@...

> http://www.ub.es/ggac

>

> tel. (+34) 93 4021373

> fax (+34) 93 4021340

>

> Fac. de Geologia,

> Univ. de Barcelona

-------------------------------------------------

Prof. Dr. K. Gerald v.d. Boogaart

Professor als Juniorprofessor fuer Statistik

http://www.math-inf.uni-greifswald.de/statistik/

office: Franz-Mehring-Str. 48, 1.Etage rechts

e-mail: Gerald.Boogaart@...

phone: 00+49 (0)3834/86-4621

fax: 00+49 (0)89-1488-293932 (Faxmail)

fax: 00+49 (0)3834/86-4615 (Institut)

paper-mail:

Ernst-Moritz-Arndt-Universitaet Greifswald

Institut f�r Mathematik und Informatik

Jahnstr. 15a

17487 Greifswald

Germany

-------------------------------------------------- - OriolIf you can get a semi-variogram from the observations which does not contain a parabolic upturn (diagnostic of polynomial type trend) then your trend is weak enough to ignore.You can download a free tutorial on dealing with polynomial type trend at http://geoecosse.bzland.com/softwaresIsobel
wrote:*Oriol Falivene <oriolfalivene@...>*Dear list,

Just a simple question...

I'm trying to produce a contour map from a structural surface. This

surface is highly non-stationary (actuaally dips towards NW)

I wolud like to know which could be the best solution for getting a

reliabel map:

1) Fit a plyonomial surface to the sample values, which is used as a

drift. Substract the drift from the observations to get the residuals.

Estimate the variogram of the residuals (now the residual variable is

stationary). Perform OK on the residuals. Add the polynomial surface to

the residuals to get the interpolated surface.

2) Compute variograms from the observations. Use universal kriging to

get the interpolated surface.

Thank you

Oriol

--

______________________________________

Oriol Falivene

ofaliven@...

http://www.ub.es/ggac

tel. (+34) 93 4021373

fax (+34) 93 4021340

Fac. de Geologia,

Univ. de Barcelona

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