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 <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> ________ ________ | \ / | 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/ <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> 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 > ================================================= > > -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org