AI-GEOSTATS: Journals

2001-01-08 Thread Isobel Clark
between wants and haves. Happy New Year to everyone Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie -- * To post a message to the list, send

Re: AI-GEOSTATS: spatial statistics for small data sets

2001-01-23 Thread Isobel Clark
uch better results if Normal (Gaussian) or normalised or transformed in some other way. If I can be of any more help, please let me know Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free

Re: AI-GEOSTATS: Block size - estimation variance - resource category.

2001-03-16 Thread Isobel Clark
--- William Thayer [EMAIL PROTECTED] wrote: Isobel: Would you mind expanding a little on your earlier reply? In particular, what do you mean by (1) "kriging variance less than ordinary statistical sample variance", (2) "not measured but within the range of influence of at least 4

Re: AI-GEOSTATS: Variowin equations and cross-validation

2001-04-10 Thread Isobel Clark
s the semi-variogram fit to the experimental with a weighted least squares. Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie -- * To post

Re: AI-GEOSTATS: Variowin equations and cross-validation

2001-04-10 Thread Isobel Clark
AAgh, sprry people, Mark Burnett just pointed out that I missed a bit in the Web reference: http://uk.geocities.com/drisobelclark/resume/Publications.html Mea culpa Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address

AI-GEOSTATS: conferences and courses

2001-04-24 Thread Isobel Clark
in 30 hours course at the IGWMC in Golden, Colorado 7-10 June 2001. Anyone who registers and turns up the day before is invited to my birthday party on 6th!! Details on the course and all other IGWMC activities can be found at http://www.mines.edu/research/igwmc/short-course/geostat.htm Isobel Clark

Re: AI-GEOSTATS: Non-Monotone Variogram model

2001-05-06 Thread Isobel Clark
to runout of pairs of samples in one or more directions somewhere around the ^ above. Try constructing directional semi-variograms and post-plotting the data to identify directional differences. Isobel Clark http://uk.geocities.com/drisobelclark

Re: AI-GEOSTATS:

2001-05-07 Thread Isobel Clark
boreholes. Inferred: anything the geologist thinks is there. Hope this helps. Isobel Clark http://uk.geocities.com/drisobelclark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie

Re: AI-GEOSTATS: The Estimation of Range paramter is very very big

2001-05-15 Thread Isobel Clark
Are you using some kind of automated fitting? The results would suggest that the model is inappropriate or that your basic assumptions are inappropriate. You should look at how the models are being fitted and what assumptions are made and question everything. Isobel Clark

Re: AI-GEOSTATS: Choosing Lag Distance and Angular Tolerance

2001-05-15 Thread Isobel Clark
in the equations so that they are non-zero. I don't know any software package (off hand ) that does this, though. Isobel Clark --- Andrew Mullens [EMAIL PROTECTED] wrote: I have a question relating to this question, certainly not to question the previous writer, it just seems like a good time

Re: AI-GEOSTATS: Number of data points Variograms

2001-05-15 Thread Isobel Clark
interesting. How do you define better -- prettier? nicer? easier to interpret? less polluted? Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie

Re: AI-GEOSTATS:

2001-05-22 Thread Isobel Clark
widely applicable. Is it a software limitation for the package mentioned? Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie -- * To post a message

Re: AI-GEOSTATS:

2001-05-23 Thread Isobel Clark
? Isobel Clark http://geoecosse.bizland.com Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie -- * To post a message to the list, send it to [EMAIL

Re: AI-GEOSTATS:

2001-05-23 Thread Isobel Clark
Excuse my persistence, but I think you are missing the point here. If you can produce a covariance function by subtracting the semi-variogram from an arbitrary constant AND if it makes no difference to the resulting equations, you are simply constructing the equations WITH the semi-variogram.

Re: AI-GEOSTATS:

2001-05-23 Thread Isobel Clark
. It does not matter because we still get the same answers in the end. Surely that is the important fact here? Isobel Clark http://uk.geocities.com/drisobelclark --- Denis ALLARD [EMAIL PROTECTED] wrote: Dear Isobel, Have you not heard of pivoting? I don't understand the point of being so

Re: AI-GEOSTATS: entering the fray

2001-05-23 Thread Isobel Clark
. It is your voices we want to hear, not us border line pensioners Isobel Clark http://uk.geocities.com/drisobelclark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http

Re: AI-GEOSTATS:

2001-05-23 Thread Isobel Clark
Thank you, Marco! My point exactly. Isobel Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie -- * To post a message to the list, send it to [EMAIL

Re: AI-GEOSTATS: Help

2001-06-21 Thread Isobel Clark
Davide Unless you get software which allows you to code samples by 'individual', the simplest way is to output the calculated semi-variogram for each individual and then use a spreadsheet to combine them, weighted by the number of pairs in each case. Isobel Clark http://geoecosse.bizland.com

Re: AI-GEOSTATS: Negative Kriging Weights Estimates

2001-08-07 Thread Isobel Clark
round a few times as there is no guarantee that the new set won't have negative weights Isobel Clark http:/uk.geocities.com/drisobelclark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free

Re: AI-GEOSTATS: Samples in a block

2001-08-28 Thread Isobel Clark
or you can type in data from the keyboard. Comments and queries to me please. Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie -- * To post

Re: AI-GEOSTATS: re: sampling

2001-08-29 Thread Isobel Clark
Hi folks Numerous apologies to anyone who downloaded Krigame over the last two days. The file got corrupted and isn't actually kriging!! New version now up. Sorry sorry sorry Isobel Clark PS: on Mark Burnett's sampling thing. In South African gold mining, they have 100 years of back sampling

Re: AI-GEOSTATS: Estimating the fixed Sill in the Elliptic Anisotropy

2001-09-04 Thread Isobel Clark
How can we estimate Sill and Range in all directions by supposing that the sill is fixed? It is usual to fit the sill to an omni-directional semi-variogram graph, since that has most pairs on all points. The ranges can then be fitted individually. The alternate is to 'contour' the

Re: AI-GEOSTATS: samples with not normal distribution

2001-09-04 Thread Isobel Clark
to your answers. Isobel Clark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie -- * To post a message to the list, send it to [EMAIL PROTECTED

Re: AI-GEOSTATS: Anisotropy with varying Range and Sill

2001-09-10 Thread Isobel Clark
Any basic Geostatistics book will show you models with varying ranges and sills with direction. Except mine. We believe that sill varying with direction is a symptom of deeper problems such as non-stationarity, trend, discontinuities, etc etc. Isobel Clark http://uk.geocities.com/drisobelclark

Re: AI-GEOSTATS: Lognormal kriging and Back Transformation

2001-09-19 Thread Isobel Clark
Colin As I already pointed out higher variance = higher lagrangian multiplier so that some of the efect is cancelled out anyway. We (Geostokos) use the following as a filter: ygiagam (proven resource): kriging variance should be less than original sample variance (total sill) less within

Re: AI-GEOSTATS: free spatial analysis software for graduate students

2001-10-03 Thread Isobel Clark
This sounds terrific! I may be a little petty here but how come this is accetable but when we talk about our totally freely distributable teaching software, I get my knuckles rapped? Isobel Clark http://uk.geocities.com/drisobelclark --- Dunrie Greiling [EMAIL PROTECTED] wrote: TerraSeer

Re: AI-GEOSTATS: Negative variances

2001-11-02 Thread Isobel Clark
Kevin There is something badly wrong with your software. With ordinary kriging, it is not possible to get negative variances. With lognormal kriging, it is not possible to get negative varianse or negative estimates unless you are using a large additive constant. Isobel Clark http

Re: AI-GEOSTATS: Declustering

2001-11-15 Thread Isobel Clark
sampling. The term 'declustering' became popular around 1982/83 and is first used widely in the proceedings of the geostatistical congress held at Lake Tahoe in September 1983. Isobel Clark http://uk.geocities.com/drisobelclark __ Do You Yahoo

RE: AI-GEOSTATS: Declustering

2001-11-16 Thread Isobel Clark
grid, you do not need to decluster as the kriging system does that for you. You can experiment with these questions using our totally free unlimited kriging game. This can be found in my 'briefcase' at http://uk.geocities.com/drisobelclark/briefcase.html Does this help? Isobel Clark

AI-GEOSTATS: Re: Kriging of multiple samples

2001-10-10 Thread Isobel Clark
accordingly. This is documented in Matheron's original works. Isobel Clark http://uk.geocities.com/drisobelclark Do You Yahoo!? Get your free @yahoo.co.uk address at http://mail.yahoo.co.uk or your free @yahoo.ie address at http://mail.yahoo.ie

AI-GEOSTATS: viruses

2001-12-06 Thread Isobel Clark
Warning If you get an empty e-mail with a return address which starts with the underscore, delete it off your system as quickly as you can. Nokia 5510 looks weird sounds great. Go to http://uk.promotions.yahoo.com/nokia/ discover

Re: AI-GEOSTATS: Extreme values?

2001-12-13 Thread Isobel Clark
a rough non-parametric approach to get to cross validation. The 'error statistics' in a cross validation exercise will often assist in identifying erroneous sample measurements. Hope this helps Isobel Clark __ Do You Yahoo!? Everything you'll ever need

Re: AI-GEOSTATS: Search Strategy

2001-12-19 Thread Isobel Clark
. Isobel Clark --- Julhendra Solin [EMAIL PROTECTED] wrote: Dear All, I am working on blasthole interpolation in open pit mine. Interpolation using ordinary kriging and grades interpolated also from above bench. Blasthole spacing about 10 m and bench height 15 m. Anybody could help me how

Re: AI-GEOSTATS: Dealing with Universal Kriging

2002-04-09 Thread Isobel Clark
. Isobel Clark __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please

RE: AI-GEOSTATS: Dealing with Universal Kriging

2002-04-10 Thread Isobel Clark
Alessandro Thanks for the contribution. If Universal Kriging is applied, there is no need for simulation or multi-indicator approaches to get a standard error, it comes with the solution. Isobel __ Do You Yahoo!? Everything you'll ever need on

Re: AI-GEOSTATS: variogram at zero ( gamma(0) ) in the kriging

2002-04-28 Thread Isobel Clark
of influence and see if your answers change. Isobel Clark http://geoecosse.bizland.com/pg2000.htm __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com -- * To post

AI-GEOSTATS: Risk Assessment with Gaussian Simulation?

2002-04-29 Thread Isobel Clark
standards. Isobel Clark __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service

Re: AI-GEOSTATS: Log transformation and zeros

2002-10-02 Thread Isobel Clark
sampled are 'some fish' areas and you just didn't catch any. Isobel Clark http://uk.geocities.com/geoecosse/news.html __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com

Re: AI-GEOSTATS: anisotropic nugget

2002-10-24 Thread Isobel Clark
with a shorter range and a component sill of the right size to make the nugget effect equal in all directions. I would. Isobel Clark http://geoecosse.bizland.com __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email

Re: AI-GEOSTATS: gaussian model

2002-11-04 Thread Isobel Clark
Carolina The gaussian semi-variogram model is so-called because the formula is basically identical to that for the Normal (or gaussian) probability distribution. There is no other necessary link with the Normal distribution. Isobel (Clark) http://uk.geocities.com/geoecosse/news.html

Re: AI-GEOSTATS: curve fitting summary

2002-11-21 Thread Isobel Clark
remember seeing a paper a few years ago by a coupl eof blokes from Pretoria University on a generalised polynomial fit which would be positive definite. I don't have it to hand but can probably track it down if given sufficient motivation ;-) Isobel Clark http://geoecosse.bizland.com/news.html

Re: AI-GEOSTATS: Standard deviation, Variance

2002-12-05 Thread Isobel Clark
. There are distributions which do not conform to this behaviour and (alas for us) the lognormal is one of them. The Central Limit theorem also does not apply to mixed distributions or in cases of non-stationarity. Mind you, neither does geostatistics Isobel Clark http

Fwd: Re: AI-GEOSTATS: Standard deviation, Variance

2002-12-06 Thread Isobel Clark
Thank you Isobel --- Donald E. Myers [EMAIL PROTECTED] wrote: Date: Fri, 06 Dec 2002 12:05:54 -0700 From: Donald E. Myers [EMAIL PROTECTED] To: Isobel Clark [EMAIL PROTECTED] Subject: Re: AI-GEOSTATS: Standard deviation, Variance I stand corrected on mistakingly attributing

Re: AI-GEOSTATS: Calculating averages

2003-01-05 Thread Isobel Clark
Hi Craig The average of a product will only equal the product of the averages if the two numbers are completely independent of one another. This is exactly analogous to the calculation of a covariance in statistics. Isobel http://uk.geocities.com/drisobelclark

Re: AI-GEOSTATS: KRIGING EVALUATION

2003-01-21 Thread Isobel Clark
this value, basically, says that your estimate is a worse estimator than just using the population mean. Isobel Clark http://geoecosse.bizland.com/news.html __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email

Re: AI-GEOSTATS: Kriging Error vs variance

2003-01-27 Thread Isobel Clark
Russell Absolutely on the spot. We call this the 'ygiagam' criterion (your guess is as good as mine) ;-) Isobel Clark http://geoecosse.bizland.com/news.html __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport

Re: AI-GEOSTATS: Observations with a known standard deviation

2003-01-30 Thread Isobel Clark
if you have a significant replication variance. Isobel Clark http://geoecosse.bizland.com/news.html __ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com -- * To post

Re: AI-GEOSTATS: Question about Block Lognormal Kriging.

2003-02-05 Thread Isobel Clark
. Isobel Clark http://geoecosse.bizland.com/news.html --- Adrian_Martínez_Vargas [EMAIL PROTECTED] wrote: Question about Block Lognormal Kriging. For the Point Lognormal Kriging the unbiased estimator of z* is z*(u)=exp[y*(u) + SigmaSK^2(u)/2] where: SigmaSK^2 simple lognormal

Re: AI-GEOSTATS: Estimation of the cross semivariogram

2003-02-14 Thread Isobel Clark
) This works best if the variables are standardised (same mean, same standard deviation) and uses all of the samples with either variable. Isobel Clark http://geoecosse.bizland.com/news.html --- Soeren Nymand Lophaven [EMAIL PROTECTED] wrote: Dear list I have a question regarding estimation

Re: AI-GEOSTATS: Variograms models

2003-02-19 Thread Isobel Clark
). Isobel Clark http://uk.geocities.com/drisobelclark/resume/Publications.html --- Serele, Charles [EMAIL PROTECTED] wrote: Hi all, Does anyboby can explain to me the origin of the variogram models: spherical and exponential ? Why the names spherical and exponential ? Sincerely

Re: AI-GEOSTATS: Cross variogram

2003-03-14 Thread Isobel Clark
probably holds for cross semi-variograms too. Calculating on logarithms is computationally simpler than calculating a relative semi-variogram. Isobel Clark http://uk.geocities.com/drisobelclark --- Digby Millikan [EMAIL PROTECTED] wrote: Hello everyone, The forumlea which I have obtained

Re: AI-GEOSTATS: large error correlation coefficient?

2003-06-15 Thread Isobel Clark
! This effect has been documented for 50 years and has variously been known as the regression effect, the mine call factor, the volume/variance effect, conditional bias and many other things (not all of them polite!). Isobel Clark http://geoecosse.bizland.com/whatsnew.htm

Re: AI-GEOSTATS: bounds of IK variograms

2003-06-16 Thread Isobel Clark
Jörg Don't confuse indicator variables with classical correlation coefficients. The maximum possible on your semi-variogram will be where all differences are 1. That is every pair is (1-0). And, of course, divided by 2. So the absolute maximum an indicator semi-variogram can show is 0.5.

Re: AI-GEOSTATS: global vs local ordinary kriging

2003-07-08 Thread Isobel Clark
Ulrich Depends how powerful your computer is, what algorithm you use to solve equations and how many data you have. Isobel http://geoecosse.bizland.com/0toKriging.htm Want to chat instantly with your online friends? Get

Re: [AI-GEOSTATS: global vs local ordinary kriging]

2003-07-11 Thread Isobel Clark
with it. Isobel Clark http://geoecosse.bizland.com/courses.htm Want to chat instantly with your online friends? Get the FREE Yahoo! Messenger http://uk.messenger.yahoo.com/ -- * To post a message to the list, send it to [EMAIL PROTECTED

Re: AI-GEOSTATS: Log-normal back transform in Webster Oliver

2003-07-28 Thread Isobel Clark
P and look for papers in the second half of the 1990s). Isobel Clark http://geoecosse.bizland.com/whatsnew.htm Want to chat instantly with your online friends? Get the FREE Yahoo! Messenger http://uk.messenger.yahoo.com

Re: AI-GEOSTATS: stratified kriging

2003-08-04 Thread Isobel Clark
Oliver We have had some success with 'modelling' stuff like soil types using indicator variables. This gives you a 'probability' map as to whether or not you are in a particular soil type (or whatever) which you could then use to modify the inclusion (or perhaps the weighting?) of your samples

Re: AI-GEOSTATS: Simulation and trends

2003-08-06 Thread Isobel Clark
I would hazard a guess that simulations done this way would underestimate the 'true' variability. Isobel {Clark} http://drisobelclark.ontheweb.com PS: could I take this opportunity to remind anyone interested that the IAMG 2003 is rapidly approaching. If you haven't registered yet, sort yourself

Re: AI-GEOSTATS: Simulation and trends

2003-08-14 Thread Isobel Clark
Adrian Thank you for the reminder of one of the strengths of Turning Bands. Certainly I have no argument with your points. However Chris' question was about how to include trend in SGS and that is what my answer is about. Isobel http://ecosse.ontheweb.com

Re: AI-GEOSTATS: values normalisation with a lot of zero!

2003-08-20 Thread Isobel Clark
constant. Isobel Clark http://ecosse.ontheweb.com/whatsnew.htm Want to chat instantly with your online friends? Get the FREE Yahoo! Messenger http://uk.messenger.yahoo.com/ -- * To post a message to the list, send

AI-GEOSTATS: Jackknife Literature Source

2003-09-01 Thread Isobel Clark
Peter May I suggest Noel Cressie's book Statistics for Spatial Data (Wiley). He has extensive discussion of jack knives, bootstraps and such like and an extensive bibliography. Isobel Clark http://geoecosse.bizland.com/whatsnew.htm

Re: AI-GEOSTATS: Lag - Distance, Variogram / Semivariogram

2003-09-04 Thread Isobel Clark
and standardised to vary between -1 and +1. The disadvantage of this approach (or the covariance function is that it is difficult to assess the nugget effect accurately. You should be concerned about your variance as it provides essential information about teh variability of your phenomenon. Isobel Clark http

Re: AI-GEOSTATS: bad regression between predicted and measured

2003-10-13 Thread Isobel Clark
Duccio There are many reasons why your interpolations may not be working. A few of these are: # you are beyond the range of influence of any distance relationship, that is you have too widely spaced sampling. # your data may have a skewed or other non-Gaussian distribution which makes both

Re: AI-GEOSTATS: Kt estimation variance

2003-10-24 Thread Isobel Clark
Sebastiano Large kriging variances have nothing to do with negative weights. The two are completely different phenomena - especially in Universal Kriging. In Ordinary Kriging the estimation variance can become as high as two times the total sill of the semi-variogram. This is a theoretical

AI-GEOSTATS: Nugget to Sill Ratio

2003-10-30 Thread Isobel Clark
Jul The nugget effect is the (semi) variance between two samples which might be taken at almost exactly the same spot. Or, expressed otherwise, the variance of replicated samples. The total sill is the variance of values within your data set (or, more strictly, within all possible samples).

AI-GEOSTATS: Re: co-kriging on data with spatial trends

2003-11-27 Thread Isobel Clark
for the trend as well as the weights. You can see how this works with uor kriging game, free to all at http://geoecosse.bizland.com/softwares Hope this helps Isobel [Clark] Download Yahoo! Messenger now for a chance to win Live

Re: AI-GEOSTATS: Moran scatterplot

2003-11-28 Thread Isobel Clark
Monica The simplest solution to your problem is to use probability paper. If you do not have easy access to this, you can download a free graph paper plotter from http://perso.easynet.fr/~philimar There are also simple algorithms to produce your own. Two populations show up on a probability

Re: AI-GEOSTATS: log-normal kriging error

2003-12-03 Thread Isobel Clark
Marta I am not familiar with the software you are using, but it looks like your lognormal standard errors are being back-transformed into 'raw' units. If this is the case part of the backtransform is to multiply the 'relative standard error' by the actual value of the estimate. That is, if your

AI-GEOSTATS: Re: sparse data problem

2003-12-05 Thread Isobel Clark
in hoping for more. We use an extremely well sampled case in our (free) tutorial analyses. Look for the GASA data which has 27 samples. An embarrassement of riches in the mid-1980s, I can assure you. Isobel Clark http://geoecosse.bizland.com/softwares

AI-GEOSTATS: basic theoretical question

2003-12-16 Thread Isobel Clark
problems with this, or further questions. Isobel [Clark] http://geoecosse.bizland.com/whatsnew.htm BT Yahoo! Broadband - Save £80 when you order online today. Hurry! Offer ends 21st December 2003. The way the internet

Re: AI-GEOSTATS: maximum kriging variance with standardized sill

2003-12-17 Thread Isobel Clark
is it right to assume the maximum kriging variance to be =2 when using a variogram with a standardized sill of 1 ?? Yes, if you are estimating the value at a point from only one sample which is outside its range of influence. Isobel http://uk.geocities.com/drisobelclark/practica.htm

Re: AI-GEOSTATS: Hypothesis Testing in a Spatial Framework

2003-12-20 Thread Isobel Clark
Warren We have had some success with a sort of hypothesis test in this regard. I had a task some years back to prove that the first area mined in a deposit was not significantly lower than could be expected by chance selection. We used a combination between 'between block variance' and a sort of

AI-GEOSTATS: Re: Rules

2004-02-06 Thread Isobel Clark
member of the list. Isobel Clark http://geoecosse.bizland.com/whatsnew.htm ___ BT Yahoo! Broadband - Free modem offer, sign up online today and save £80 http://btyahoo.yahoo.co.uk -- * To post a message

Re: AI-GEOSTATS: Re: polygon kriging

2004-02-22 Thread Isobel Clark
Chaosheng This is very true that if you grid a grid of points inside a polygonal area then average them, you get exactly the same answer as if you kriged the polygon average directly. The differences are two: (1) you have to do at least 64 krigings to get within 1% of the correct average

Re: AI-GEOSTATS: modelling_dem_point

2004-02-25 Thread Isobel Clark
Ines It isn't usually a good idea to go pushing your data to where you would like them to be. A good way to determine natural spacing is to carry out a 'nearest neighbour' analysis. If data are on a grid, the best spacing is 0.2 times grid size. This keeps single grid spacing separate from

AI-GEOSTATS: Re: average semi-variogram

2004-03-01 Thread Isobel Clark
Koen I think it's called a block to block variogram average, not sure. It is called the within block variance. Block to block variance is the variance between block averages - i.e. from block to block. As I explained, I'm looking for an easy way to estimate the gamma(V,V) value. If you have

AI-GEOSTATS: Re: mixtures of populations

2004-03-09 Thread Isobel Clark
. We have had good experience with this approach for 30 years in fields as diverse as mineral resource estimation and seabird preservation. Isobel Clark http://geoecosse.bizland.com/courses.htm

AI-GEOSTATS: Re: mixtures of populations

2004-03-09 Thread Isobel Clark
way of checking - and very quick and easy to produce nowadays. I am open to any other suggestions on how to identify multiple populations when all you have is the sample data. Isobel Clark http://uk.geocities.com/drisobelclark

Re: [ai-geostats] problem regarding variogram

2004-06-07 Thread Isobel Clark
snehamoy when you say positively skewed do you mean skewed to the left or to the right. If you calculate the skewness coefficient, postive is skewed to the left with a long tail to the right. If your data is skewed to the right, it is negatively skewed. For negative skewness, we have had

[ai-geostats] Re: kriging proportions

2004-06-10 Thread Isobel Clark
Marc-Olivier The simplest solution - in the sense that most packages could handle it - is to carry out a 'nested' indicator analysis. That is: (i) code one of your particle classes as '1' and all other as '0', produce a map of proportion of this class. (ii) remove this particle class from

Re: [ai-geostats] variograms

2004-07-08 Thread Isobel Clark
Salah If your data is irregularly spaced, then you need to experiment with 'lag' intervals to balance between (a) getting enough points to see the shape of the graph and (b) getting enough pairs in each point to have some confidence in it. Remember that each point on your graph is an

[ai-geostats] Re: Kriging Small Blocks

2004-07-19 Thread Isobel Clark
Jul The warning about kriging small blocks is about small relative to the sampling density. For example, less than about one-third of the grid spacing. The warning is the same as the one about 'point' kriging (mapping) The map is too smooth - or, at least, a lot smoother than the real surface

[ai-geostats] Re: Kriging Small Blocks

2004-07-19 Thread Isobel Clark
recipient. If you have received this message by mistake, please notify the sender and delete the message immediately. Be aware that the unauthorized use of the above-mentioned information is strictly forbidden. -Mensagem original- De: Isobel Clark [mailto:[EMAIL PROTECTED] Enviada em

[ai-geostats] Re: Kriging Small Blocks

2004-07-19 Thread Isobel Clark
Ed I would differ from your explanation on one point. If you are merely declaring a mineral resource, i.e. mineral in the ground, then the conditional bias may not be relevant at the pre feasibility stage. However, as soon as you introduce any economic or technical parameters which entail

[ai-geostats] spatial relationships

2004-09-01 Thread Isobel Clark
Mark I could not agree more with Gregoire (with one proviso, see below). Both geostatistics and any weighted average estimators are based on the same assumptions -- that relationship between values at two locations depends on the distance between them and (possibly) their relative orientation.

[ai-geostats] spatial relationships

2004-09-02 Thread Isobel Clark
Dear oh Dear, I am failing to communicate (again). As far as I know, I didn't say you could not use geostatistics when a trend is present! I regularly use Universal Kriging for data with a trend and kriging with an external drift when the trend is governed by an outside factor (see free tutorial

[ai-geostats] Re: Frightened of Spatial Autocorrelation

2004-09-02 Thread Isobel Clark
Kevin Sounds like an ideal case for Geographically Weighted Regression. You could use semi-variograms or spatial auto-correlation to determine exactly how proximity defines relationship. My only current beef with GWR is the seemingly pre-defined distance weighting functions. Not had much time

Re: [ai-geostats] A question on lag class and lag distance

2004-10-01 Thread Isobel Clark
xhy your questions are long-standing and as yet unanswered in general. 1. How to select the lag class and lag distance in order to obtain a more reasonable experimental variogram? I always think of it as focussing a camera. Believe there is a pattern in your data and our task is to balance

[ai-geostats] Re: Sample data sets

2004-10-18 Thread Isobel Clark
Mark We have about 13 data sets available on our free download site, ranging from mining data to fisheries, agriculture and environmental stuff. Number of data ranges from 27 to 20,000. Download from http://geoecosse.bizland.com/softwares and find details and references for most of them at

[ai-geostats] Re: regularization

2004-10-26 Thread Isobel Clark
Samuel Practical Geostatistics (1979) Chapter 3. Get it for free at http://uk.geocities.com/drisobelclark/practica.htm Isobel http://geoecosse.bizland.com/books.htm * By using the ai-geostats mailing list you agree to follow its rules ( see http://www.ai-geostats.org/help_ai-geostats.htm ) *

Re: [ai-geostats] problem of spatial continuity of groundwater head

2004-11-23 Thread Isobel Clark
Kai I would suggest you take a look at: Introduction to Geostatistics: Applications in Hydrogeology (Stanford-Cambridge Program) P. K. Kitanidis which is a great base to work from. Isobel http:///geoecosse.bizland.com * By using the ai-geostats mailing list you agree to follow its rules (

[ai-geostats] F and T-test for samples drawn from the same p

2004-12-04 Thread Isobel Clark
Don Thank you for the extended clarification of F and t hypothesis test. For those unfamiliar with the concept, it is worth noting that the F test for multiple means may be more familiar under the title Analysis of variance. My own brief answer was in the context of Colin's question, where it

[ai-geostats] RE: F and T-test for samples drawn from the same p

2004-12-05 Thread Isobel Clark
Colin Daly -Original Message- From: Chaosheng Zhang [mailto:[EMAIL PROTECTED] Sent: Sun 12/5/2004 11:42 AM To: [EMAIL PROTECTED] Cc: Colin Badenhorst; Isobel Clark; Donald E. Myers Subject: Re: [ai-geostats] F and T-test for samples drawn from the same p Dear all

Re: [ai-geostats] Re: F and T-test for samples drawn from the same p

2004-12-07 Thread Isobel Clark
Digby I see where you are coming from on this, but in fact the sill is composed of those pairs of samples which are independent of one another - or, at least, have reached some background correlation. This is why the sill makes a better estimate of the variance than the conventional statistical

[ai-geostats] Sill versus least-squares classical variance estimate

2004-12-07 Thread Isobel Clark
Meng-Ying We are talking about estimating the variance of a set of samples where spatial dependence exists. The classical statistical unbiassed estimator of the population variance is s-squared which is the sum of the squared deviations from the mean divided by the relevant degrees of freedom.

[ai-geostats] variogram analysis

2004-12-08 Thread Isobel Clark
Rajive I haven't read the other responses yet, so this may be redundant. Two possibilities: (1) anisotropy: if this is shallow marine data there should be a difference between longshore drift and off-shore deepening of sea-bed. You have an omni-directional semi-variogram. It is possible that

[ai-geostats] Re: Sill versus least-squares classical variance estimate

2004-12-08 Thread Isobel Clark
be able to clarify the things you clarifies. You're good. Meng-ying On Wed, 8 Dec 2004, Isobel Clark wrote: Meng-Ying I don't know how to say this any other way. At distances larger than the range of influence, samples are NOT SPATIALLY CORRELATED. The variance

[ai-geostats] descriptive statistics or inference?

2004-12-08 Thread Isobel Clark
And just a personal opinion, I would like to think geostatistic theories apply to population of any size, as small as 27, or as large as 1,000,000. If I'm making an example that geostatistics doesn't apply, then there's something to concern about in this approach. Geostatistics applies to

[ai-geostats] within line variance

2004-12-09 Thread Isobel Clark
Meng-Ying Assuming that you generated your line with a Spherical model, range 3, 27 samples making 9 ranges the variance within that line will (theoretically) be 0.9191 of the semi-variogram sill. Of course this theory depends on you have every possible sample in that length, not just 27 of

[ai-geostats] Re: descriptive statistics or inference?

2004-12-12 Thread Isobel Clark
Digby The variance/sill relationship is theoretical and does not depend on the layout of the samples, regular or clustered. Since the sill only uses pairs where samples are uncorrelated from one another, the clustering is irrelevant. It does depend on the distribution of the samples values being

  1   2   >