This is one awesome discussion - sounds better than the symposiums !! Maybe we must clarify a few points by Steven! 1) What manager in the mining or petroleum industry who has graduated from college hasn't taken a serious statistics course, including covariances and correlations? >> I am a geologist with ten years mining experience in South Africa. It is part of my job to try and implement geostatistical techniques in grade estimations on the mines. The mining/geological managers knows how to take ore out of the ground and sell it. They would not be bothered by the covariance or the difference approach - the only thing is that there is BIG problems if the actual plant feed grade is lower than predicted grade. Then the true colors of the managers come out and the in-house geostatician has lots of problems. If the in-house geostatician can blame it on the outside consultant/instructor then he might survive. 2) Surely when starting from scratch, educating someone about geostatistics is more intuitive using covariances? (Just my opinion so far, speaking as a mathematician who remembers teaching basic college level statistics to nursing majors, education majors, sociology majors, etc. And even succeeding occasionally.) >> From my personal experience in trying to explain to managers why they should not use polygonal or inverse distance estimates on their mine, it was much easier to explain it with the difference method. The discussion would normally be around samples from drillholes (which the managers always refers to as being expensive) which are more different at larger distances and hopefully less different at closer distances. Which is why the geologist likes to drill at closer distances - it also tends to make the plant grade feed predictions more accurate. 3) I have taken two multi-day courses in geostatistics from well known industry experts. In each class they included significant material and time on the first day explaining/justifying variograms by showing their mathematical relationship to spatial covariance functions. It seems that those instructors did not trust the variogram to be more intuitive than spatial covariance functions. >> I have been in a few practical geostats courses where the students are a mix of surveyors, miners, samplers, grade control officers and geologists. Somehow it always seems to be easier for the instructor to use the difference method to explain variography. 4) The two basic level introductions to geostatistics I have on my bookshelf replicate the experience at those two classes.... >> As a practicing geostatician on a producing mine the reality is that we can have huge discussions on the mathematical delicacy's of pivoting the Kriging equations etc. but the feed grade to the plant or ore beds must be in close proximity of what was predicted. The big mining companies and banks are spending huge amounts of capital on mining ventures and the grade/tonnage curves (or block model as some people call it) plays a significant part in the decision. And any industry geostats course must be practical enough so that the students can go back and make accurate grade/tonnage curves. That's what pays the bills. I don't know if I am getting the message through - the big mining companies needs the practical experience because the "proof of the pudding lies in the plant feed" Ian Hunt -----Original Message----- From: Yetta Jager [SMTP:[EMAIL PROTECTED]] <mailto:[SMTP:[EMAIL PROTECTED]]> I think part of the difficulty in the semivariogram vs. covariance war is that modeling is subjective, and the notion of covariance has become more intuitive for statisticians, while the notion of semivariance has become more intuitive for geologists. From: Isobel Clark [[EMAIL PROTECTED]] I agree that the semi-variogram approach is easier for the non-statistician to grasp. Difference in value is a simpler concept to grasp than cross-product, especially when your boss wants to know the likely difference between what you tell him and what really happens! -- * 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 -- * 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
AI-GEOSTATS: entering the fray again
Ian Hunt [KLP BUSINESS DEVELOPMENT] Thu, 24 May 2001 00:11:17 -0700
