How to create a lithotype rule for Pluri-Gaussian models?

How to use RGeostats package step-by-step.
Direct access to Tutorial index and Frequently Asked Questions

How to create a lithotype rule for Pluri-Gaussian models?

Postby Nicolas Desassis » Sat Jul 12, 2014 9:48 pm

The rule (or lithotype rule) is an essential object to perform plurigaussian simulation.
Note that in RGeostats, the categories (also called lithotype, facies, ...) are coded by using integers between 1 and the number of categories. The rules involve one or two Gaussian Random Functions (GRFs) and can be created according to two ways:

By using an interface with the function

Code: Select all
rule.input


or with the command line by using

Code: Select all
rule.create


1) A simple rule

We start this tutorial by showing how to create the simplest (non trivial) rule: a rule involving 1 GRF to model 2 facies.

The command

Code: Select all
rule=rule.input()


provides an interface as follows (the answers are indicated in red and explanations are given hereafter):


Choose the Rule Definition mode
0 : Standard definition of GRF
1 : Definition of one GRF with Shift
2 : Definition of one GRF with Shadow
Rule Definition mode [0,2] : 0
Correlation between the two GRFs (Def=0.000000) [0.000000,1.000000] : 0

Enter the Lithotype Rule (recursively)
Use 'F' (Facies), 'S' (Threshold Y1), 'T' (Threshold Y2) or 'stop'
Choice of node 'main' [F,S,T] : S
Use 'F' (Facies), 'S' (Threshold Y1), 'T' (Threshold Y2) or 'stop'
Choice of node 'S1 [Low]' [F,S,T] : F
Enter the Facies value [1,NA] : 1
Use 'F' (Facies), 'S' (Threshold Y1), 'T' (Threshold Y2) or 'stop'
Choice of node 'S1 [Sup]' [F,S,T] : F
Enter the Facies value [1,NA] : 2


The first answer will always be 0 in this tutorial since the other modes should become obsolete in a future version.
The second one indicates the correlation coefficient between the two GRFs (i.e the value of the cross-covariance at distance 0).
This value has to be consistent with the bivariate spatial model.
However, this is currently irrelevant since we are creating a rule for only one GRF (we have answered 0)
After that, we answer S which indicates that we want to divide the current window in two.
Then we have to answer how to fill the left part of the window. We have answered F which indicates that we want to fill it with a facies and then 1 to say that it is the first one.
Then we are asked to say how we want to fill the right window. We have answered F then 2 to fill it with the facies 2.

To obtain the same result as previously without any interface, we can use:

Code: Select all
rule=rule.create(c("S","F1","F2"))
plot(rule)


Try also:

Code: Select all
rule=rule.create(c("S","F2","F1"))
plot(rule)
Nicolas Desassis
 
Posts: 196
Joined: Thu Sep 20, 2012 4:22 pm

Return to Tutorials and FAQ

Who is online

Users browsing this forum: No registered users and 0 guests

cron