## RE: [ai-geostats] modelling trend and kriging type

Expand Messages
• Perry Your basic semi-variogram graph has a parabola added to it. Shoots off upwards (usually) at some distance. If the distance is large (past the range of
Message 1 of 10 , Jul 7, 2005
• 0 Attachment
Perry

Your basic semi-variogram graph has a parabola added to it. Shoots off upwards (usually) at some distance. If the distance is large (past the range of influence) you can ignore it. See some of our  mid-80s papers on the Wolfcamp data which lots of people use as a teaching set now. Or read my free tutorial at http://geoecosse.bizland.com/softwares (kriging with trend).

Isobel

PCollier@... wrote:

Hi all

I may know this already, but what are the symptoms of data with a trend?  What is the difference between a dataset with a trend and a non-stationary dataset?

Cheers

Perry Collier

Senior Mine Geologist
Ernest Henry Mine
Xstrata Copper Australia
Ph (07) 4769 4527
Fx (07) 4769 4555
E-mail PCollier@...
Web http://www.xstrata.com

PO Box 527
Cloncurry QLD 4824
Australia

"Light travels faster than sound. That is why some people appear bright
until you hear them speak"

-----Original Message-----
From: Pierre Goovaerts [mailto:Goovaerts@...]
Sent: Friday, 1 July 2005 12:54 AM
To: Recep kantarci; ai-geostats@...
Subject: RE: [ai-geostats] modelling trend and kriging type

1. Universal kriging = kriging with a trend. The second terminology has been proposed by Andre
Journel who felt that the term "universal" was vague and misleadingly "ambitious".

2. Kriging with an external drift (KED) is mathematically the same as universal kriging (UK). Secondary variables
are simply replacing the spatial coordinates used in UK.

3. Regression kriging denotes all the techniques where the trend is modeled outside the kriging algorithm.
There are various methods that can be used to model that trend, ranging from linear regression
to neural networks. Kriging is used to interpolate the residuals. In practice these techniques have more
flexibility than universal kriging in term of modeling the trend: multiple variables either categorical or
continuous can be incorporated  easily and many sofwtare are available for this trend modeling.
The only limitation is that the trend is modeled globally (i.e. the regression coefficients are constant
in space) while in KED the coefficients are reestimated within each search window.

Cheers,

Pierre

Pierre Goovaerts

Chief Scientist at Biomedware

516 North State Street

Ann Arbor, MI 48104

Voice: (734) 913-1098
Fax: (734) 913-2201

http://home.comcast.net/~goovaerts/

-----Original Message-----
From: Recep kantarci [mailto:recep_kantarci_1978@...]
Sent: Thu 6/30/2005 9:38 AM
To: ai-geostats@...
Cc:
Subject: [ai-geostats] modelling trend and kriging type

Dear ai-geostats members

When the data used has a trend, it is needed to model trend and in this case there exists various types of kriging to apply (universal kriging, kriging with a trend, regression kriging etc).

If this is the case, does one should use the same type of kriging or different depending on modeling the trend using coordinates of target variable or using other (namely, secondary or auxillary) variables such as elevation or topography ? That is , are there a dinstinction depending on the type of variables to model the trend while kriging?

Best regards
Recep

_____

Yahoo! kullaniyor musunuz?
http://tr.mail.yahoo.com <http://tr.mail.yahoo.com/>

**********************************************************************

The information contained in this e-mail is confidential and is

intended only for the use of the addressee(s).

If you receive this e-mail in error, any use, distribution or

copying of this e-mail is not permitted. You are requested to

forward unwanted e-mail and address any problems to the

Xstrata Queensland Support Centre.

Support Centre e-mail: supportcentre@...

Support Centre phone: Australia 1800 500 646

International +61 2 9034 3710

**********************************************************************

* By using the ai-geostats mailing list you agree to follow its rules
( see http://www.ai-geostats.org/help_ai-geostats.htm )

* To unsubscribe to ai-geostats, send the following in the subject or in the body (plain text format) of an email message to sympa@...

Signoff ai-geostats
• Hi Perry, I am curious to see how others will reply to your second question on the difference between a dataset with a trend and one that is non-stationary! My
Message 2 of 10 , Jul 7, 2005
• 0 Attachment
Hi Perry,

I am curious to see how others will reply to your second question on the
difference between a dataset with a trend and one that is
non-stationary! My reply may sound provocative: you can always remove a
trend when you recognize that there is one. Moving from non-stationarity
to stationarity, on the other hand, can be infinitely more complex (e.g.
moving to non-Euclidean space)

:)

For what concerns the detection of trends, have a look at the variogram:
a quadratic/exp. increase usually means that there is a trend. Get rid
of the presumed trend and check the variogram of the residuals which
should clearly show a change of structure (if you had a trend
obviously). Quicker might be to use a moving windows strategy to plot
local averages and check if you see any structure (be careful that the
"structure" is not simply an anisotropy of your variable). You could
have a look into the old archives of AI-GEOSTATS. There have been very
nice replies from Donald Myers (see his publications) in the past on
these issues. see http://groups.yahoo.com/group/ai-geostats/

Regards

GD

-----Original Message-----
From: PCollier@... [mailto:PCollier@...]
Sent: 07 July 2005 03:49
To: ai-geostats@...
Subject: RE: [ai-geostats] modelling trend and kriging type

Hi all
I may know this already, but what are the symptoms of data with a trend?
What is the difference between a dataset with a trend and a
non-stationary dataset?
Cheers

Perry Collier
Senior Mine Geologist
Ernest Henry Mine
Xstrata Copper Australia
Ph (07) 4769 4527
Fx (07) 4769 4555
E-mail PCollier@...
Web http://www.xstrata.com

PO Box 527
Cloncurry QLD 4824
Australia

"Light travels faster than sound. That is why some people appear bright
until you hear them speak"

-----Original Message-----
From: Pierre Goovaerts [mailto:Goovaerts@...]
Sent: Friday, 1 July 2005 12:54 AM
To: Recep kantarci; ai-geostats@...
Subject: RE: [ai-geostats] modelling trend and kriging type

1. Universal kriging = kriging with a trend. The second terminology has
been proposed by Andre
Journel who felt that the term "universal" was vague and misleadingly
"ambitious".

2. Kriging with an external drift (KED) is mathematically the same as
universal kriging (UK). Secondary variables
are simply replacing the spatial coordinates used in UK.

3. Regression kriging denotes all the techniques where the trend is
modeled outside the kriging algorithm.
There are various methods that can be used to model that trend, ranging
from linear regression
to neural networks. Kriging is used to interpolate the residuals. In
practice these techniques have more
flexibility than universal kriging in term of modeling the trend:
multiple variables either categorical or
continuous can be incorporated easily and many sofwtare are available
for this trend modeling.
The only limitation is that the trend is modeled globally (i.e. the
regression coefficients are constant
in space) while in KED the coefficients are reestimated within each
search window.

Cheers,

Pierre

Pierre Goovaerts
Chief Scientist at Biomedware
516 North State Street
Ann Arbor, MI 48104
Voice: (734) 913-1098
Fax: (734) 913-2201
http://home.comcast.net/~goovaerts/
-----Original Message-----
From: Recep kantarci [mailto:recep_kantarci_1978@...]
Sent: Thu 6/30/2005 9:38 AM
To: ai-geostats@...
Cc:
Subject: [ai-geostats] modelling trend and kriging type

Dear ai-geostats members

When the data used has a trend, it is needed to model trend and
in this case there exists various types of kriging to apply (universal
kriging, kriging with a trend, regression kriging etc).
If this is the case, does one should use the same type of
kriging or different depending on modeling the trend using coordinates
of target variable or using other (namely, secondary or auxillary)
variables such as elevation or topography ? That is , are there a
dinstinction depending on the type of variables to model the trend while
kriging?

Best regards
Recep

_____
Yahoo! kullaniyor musunuz?
korunma Yahoo! Posta'da
http://tr.mail.yahoo.com <http://tr.mail.yahoo.com/>
**********************************************************************
The information contained in this e-mail is confidential and is
intended only for the use of the addressee(s).
If you receive this e-mail in error, any use, distribution or
copying of this e-mail is not permitted. You are requested to
forward unwanted e-mail and address any problems to the
Xstrata Queensland Support Centre.
Support Centre e-mail: supportcentre@...
Support Centre phone: Australia 1800 500 646
International +61 2 9034 3710
**********************************************************************
Your message has been successfully submitted and would be delivered to recipients shortly.