Hello,
In the past few years stochastic simulation has
been increasingly used to produce probability maps.
To my opinion it's generally a waste of CPU time since
similar information can be retrieved using kriging,
either in a multiGaussian framework or applied to
indicator transforms.
The issue of when using simulation vs kriging
is further discussed in:
Goovaerts, P. 2001.
Geostatistical modelling of uncertainty in soil science.
Geoderma, 103: 3-26.
I take this opportunity to thank Gregoire
for a remarkable and often challenging job
of keeping this e-mail list alive through the years.
Pierre
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________ ________
| \ / | Pierre Goovaerts
|_ \ / _| Assistant professor
__|________\/________|__ Dept of Civil & Environmental Engineering
| | The University of Michigan
| M I C H I G A N | EWRE Building, Room 117
|________________________| Ann Arbor, Michigan, 48109-2125, U.S.A
_| |_\ /_| |_
| |\ /| | E-mail: [EMAIL PROTECTED]
|________| \/ |________| Phone: (734) 936-0141
Fax: (734) 763-2275
http://www-personal.engin.umich.edu/~goovaert/
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On Sat, 27 Apr 2002, Chaosheng Zhang wrote:
> Dear list,
>
> First, I would like to say thank you to Gregoire for keeping this list alive.
>
> I'm trying to do "risk assessment", and I have some questions about risk assessment
>with Gaussian Simulation:
>
> (1) How to produce a probability map?
>
> With Gaussian simulation, we can produce many maps/realisations, e.g., 100. Based on
>the 100 maps, a probability map of higher than a threshold can be produced. I wonder
>how to produce such a probability map? My understanding is that for each pixel, we
>just count how many values out of the 100 are >threshold, and the number is regarded
>as the "probability". Am I right? It seems that this is a time consuming procedure
>with GIS map algebra. Are there any suggestions for a quick calculation?
>
> (2) Is a probability map better than a Kriging interpolated map for the purpose of
>risk assessment?
>
> (3) Is "PCLASS" function in IDRISI 32 Release 2 better/easier than the probability
>map from Gaussian simulation?
>
> >From the online help of IDRISI 32 R2, Section "Kriging and Simulation Notes", it
>says "If the final goal of simulated surfaces will be to directly reclassify the
>surfaces by a threshold value, and calculate a probability of occurrence for a
>process based on that threshold, conditional simulation may be unnecessary. Instead
>kriging and variance images may be created and then used together with PCLASS." Any
>comments?
>
> (4) How to carry out "PCLASS"?
>
> Following the above question, I have a problem in doing PCLASS. I cannot input the
>file name of Kriging variance to the field of "Value error" of the documentation
>file. It seems that this field only accepts a "value", not an "image file name" or
>anything in text. Anyone has the experience?
>
> Cheers,
>
> Chaosheng Zhang
> =================================================
> Dr. Chaosheng Zhang
> Lecturer in GIS
> Department of Geography
> National University of Ireland
> Galway
> IRELAND
>
> Tel: +353-91-524411 ext. 2375
> Fax: +353-91-525700
> Email: [EMAIL PROTECTED]
> [EMAIL PROTECTED]
> Web: http://www.nuigalway.ie/geography/zhang.html
> =================================================
>
>
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