Re: AI-GEOSTATS: average semi-variogram
Note that gamma(V,V) is a variogram model property, not a data property: in the figure you mention, the big dots are data points, the small dots discretize the block but do not indicate observed data. I know that you can discretize block estimates with a pretty good accuracy with a limited amount of points. But, I was convinced that I could use grided observed data and gamma(V,V) as an estimate for the variance within my grided block. To clarify, I did measure the point values in a grid in a plot/block. I don't have to estimate them, I just need a spacially depended estimate of the whole plot/block variance. The problem is that I would like to automate the procedure of calculating that within block variance because variogram models need to be fit visually most of the time, wich is time consuming. When repeating calculations on randomized data this isn't an option. So if gamma(V,V) really is model property rather then a data property I have a problem... If you can see the trees for the forest, because I don't. Koen. -- * 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
Re: AI-GEOSTATS: average semi-variogram
Hello Koen Matlab is very slow because it's only an interpreter language, dealing with every line code at a time. You can compile matlab functions with the invoked mcc or any other compiler to make things faster (not calculating the time you need to learn how things are going). kind regards, Ralf Stosius > To clear things up, > > I want to calculate the variance of values within an area (20x20m). > > So you calculate the semi-variogram value from each point to every other > point in that area, you add up all the terms and divide by the number of > terms/pairs. > > I think it's called a "block to block" variogram average, not sure. > > A link to an illustration: > > http://www.houlding.net/simon/DVEpaper/DVEfig03.htm > > As I explained, I'm looking for an easy way to estimate the gamma(V,V) > value. > > I used matlab to code for the distances between pairs but, it takes so > much time compared to geoR or gstat that I doubt I'm working correctly or > these packages are optimized in some way to cut back on calculation times.. > Bottom line is that I don't want to spent to much time coding stuff and > more time doing the actual analysis. > > Koen... > > > Hi, > > > > what do you mean by average semi-variance? The semivariance at any lag is > > always going to be the average of the semivariance between many lag pairs > > (the exact number depends on sample size, spacing etc). As far as I am > > aware > > R calculates the average semivariance for each lag and presents this as > > the > > "experiemental semivariogram". Other softwarre provide the variogram > > cloud, > > the values of individual pair comparisons, from which the experimental > > variagram is averaged, > > > > hope this helps > > > > Benjamin > > -- > * 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: DEM-interpolation method
Dear member list I used contour line and few elevation points to generate a DEM, the first interpolator that I used was been the TIN interpolator but the RMS was been not very good, so I converted all nodes of the contour lines into elevation points and I used them to produce many model based on IDW, RBS and KRIGING interpolators. Using these interpolators I obtained a good results. My question is: it has meaning to convert all node of the contour lines in points and use them to generate a DEM with different interpoators that ask points as input data?
Re: AI-GEOSTATS: average semi-variogram
gstat (either flavour) does calculate gamma(V,V) on its way to get to block kriging predictions, but has no special way of reporting this value; you probably get it (along with much much more info) on your screen when you set debug value to 32, and do a block kriging with your given variogram model. Note that gamma(V,V) is a variogram model property, not a data property: in the figure you mention, the big dots are data points, the small dots discretize the block but do not indicate observed data. -- Edzer Koen Hufkens wrote: To clear things up, I want to calculate the variance of values within an area (20x20m). So you calculate the semi-variogram value from each point to every other point in that area, you add up all the terms and divide by the number of terms/pairs. I think it's called a "block to block" variogram average, not sure. A link to an illustration: http://www.houlding.net/simon/DVEpaper/DVEfig03.htm As I explained, I'm looking for an easy way to estimate the gamma(V,V) value. I used matlab to code for the distances between pairs but, it takes so much time compared to geoR or gstat that I doubt I'm working correctly or these packages are optimized in some way to cut back on calculation times. Bottom line is that I don't want to spent to much time coding stuff and more time doing the actual analysis. Koen... Hi, what do you mean by average semi-variance? The semivariance at any lag is always going to be the average of the semivariance between many lag pairs (the exact number depends on sample size, spacing etc). As far as I am aware R calculates the average semivariance for each lag and presents this as the "experiemental semivariogram". Other softwarre provide the variogram cloud, the values of individual pair comparisons, from which the experimental variagram is averaged, hope this helps Benjamin -- * 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.or g -- * 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: Re: average semi-variogram
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 a standard semi-variogram model such as the spherical or exponential, the mathematical formulae for two dimensional blocks are published in various issues of Computers and Geosciences. Point approximations are only necessary if you have a non-readitional model or rotational geometric anisotropy. > I used matlab to code for the distances between > pairs but, it takes so much time compared to . Most software packages use the symmetry of the block so that only about one-quarter of the calculation need to be carried out. You can get the within block variance from our kriging game for all the models we cover. It is written onto the screen and the ghost file as you work. Just select the option to estimate a rectangular block. http://geoecosse.bizland.com/softwares Isobel ___ Yahoo! Messenger - Communicate instantly..."Ping" your friends today! Download Messenger Now http://uk.messenger.yahoo.com/download/index.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
Re: AI-GEOSTATS: average semi-variogram
To clear things up, I want to calculate the variance of values within an area (20x20m). So you calculate the semi-variogram value from each point to every other point in that area, you add up all the terms and divide by the number of terms/pairs. I think it's called a "block to block" variogram average, not sure. A link to an illustration: http://www.houlding.net/simon/DVEpaper/DVEfig03.htm As I explained, I'm looking for an easy way to estimate the gamma(V,V) value. I used matlab to code for the distances between pairs but, it takes so much time compared to geoR or gstat that I doubt I'm working correctly or these packages are optimized in some way to cut back on calculation times. Bottom line is that I don't want to spent to much time coding stuff and more time doing the actual analysis. Koen... Hi, what do you mean by average semi-variance? The semivariance at any lag is always going to be the average of the semivariance between many lag pairs (the exact number depends on sample size, spacing etc). As far as I am aware R calculates the average semivariance for each lag and presents this as the "experiemental semivariogram". Other softwarre provide the variogram cloud, the values of individual pair comparisons, from which the experimental variagram is averaged, hope this helps Benjamin -- * 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
