AI-GEOSTATS: Estimating the fixed Sill in the Elliptic Anisotropy
Hi, AI-Geostats member In Elliptic Anisotropy we suppose that the Sill parameter of Variogram is fixed and the Range parametre is varying with direction, in an ellipce. But in practice, usually Sill is also depends to direction (more or less). My question is that: How can we estimate Sill and Range in all directions by supposing that the sill is fixed? (With traditional methods in statistics: OLS, WLS,..). NOTE that in the traditional Variogram Model fitting, where we estimate the range and the sill in each direction ,seperately, we yield different sills in different directions, EVEN THE DATA SIMULATED FROM AN ISOTROPIC RANDOM FIELD! Yours Sincerely: Y. Waghei Dep.of Biostatistics Tarbiat Modarres Un. Tehran Tel:8011001-3872 ___ Visit http://www.visto.com. Find out how companies are linking mobile users to the enterprise with Visto. -- * 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: Estimating the fixed Sill in the Elliptic Anisotropy
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 experimental semi-variograms in many directions and fit one ellipoidal surface to the 'map'. 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 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: samples with not normal distribution
Hi everybody! I know I am going to make a quite silly questions for people who is used to work with krigging, but I am quite new, and after reading three different books and talk to 2 or three people I am in a mess: is it correct to interpolate data from a sample that doesn't follow a normal distribution? I have tried to get it transforming data with log, but the distribution of these new data is still not normal. Thanks to everybody Montse Ferrer University of Salamanca Dpt Geography Spain [EMAIL PROTECTED] -- * 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: samples with not normal distribution
What does your data look like after you take logarithms? Is it still skewed? If you do a probability plot does it drop off at the lower end? Or at the top? or is it still curved? Or does it have a kink in it? Geostatistics is possible with any or all of the above but the remedy differs according 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] * 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: spatial autocorrelation
Hello, I'm helping someone with some spatial analyses for some data with plant species data across a set of natural pools. We are trying to determine whether there is spatial autocorrelation, but am not sure what test to run. At first I was advised that perhaps using the Moran's I index would work, but I have had some folks suggest that Moran's I works best for adjacent polygons or raster data. I am using an ArcView polygon data layer. Another recommendation was to use semivariograms included in Geostatistical Analyst with ArcView 8.1, which I will attempt in the coming week. I have a few questions. My first question is: What is the appropriate test that should be employed to determine whether there is spatial autocorrelation given this scenario? There are approximately 100 natural pools that have varying abundances of the plant in question. However, only 32 pools were sampled. It was not a random sampling...out of the 100 pools, these were the only ones that were not damaged by construction. The other pools are still functional, however, and do contain the plant being studied. On one end of the site most of the pools were sampled, whereas on the other end of the site only a few pools were sampled. So my second question is: Can I really test for spatial autocorrelation if we do not have any data for the damanged pools? My concern is that we will have a sampled pool with high plant density next to 4 or 5 non-sampled pools...will we get the wrong outcome? I don't know if this makes sense...it's difficult to explain virtually! If anyone has any suggestions I'd really appreciate it! Thanks very much in advance, Sue --- Sue Rodriguez-Pastor Dept. of EPO Biology University of Colorado email address: [EMAIL PROTECTED] --- -- * 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: spatial autocorrelation
On Tue, 4 Sep 2001, Sue Rodriguez-Pastor wrote: Hello, I'm helping someone with some spatial analyses for some data with plant species data across a set of natural pools. We are trying to determine whether there is spatial autocorrelation, but am not sure what test to run. At first I was advised that perhaps using the Moran's I index would work, but I have had some folks suggest that Moran's I works best for adjacent polygons or raster data. I am using an ArcView polygon data layer. This is not necessarily true, there has been some use of moran's I in the metapopulation literature. See for instance the chapter by Michael Gilpin in the 1997 Hanski and Gilpin book on metapopulations. Also Epperson has written quite a few papers on population genetic models using moran's I for disjunct populations. You do need to be very careful how you define your wieght matrix. Another recommendation was to use semivariograms included in Geostatistical Analyst with ArcView 8.1, which I will attempt in the coming week. As above be careful. Geostatistics assummes an underlying continous model where as in this situation you have sites on the nodes of a graph. The unsampled locations are really a problem because any measure of connectivity in your system would need to include all the ponds. What is your overall question you are trying to answer? Is it related to the persistance of the metapopulation? Is it about dispersal? More information on what you are really trying to ask biologically might help to suggest an approach. Nicholas I have a few questions. My first question is: What is the appropriate test that should be employed to determine whether there is spatial autocorrelation given this scenario? There are approximately 100 natural pools that have varying abundances of the plant in question. However, only 32 pools were sampled. It was not a random sampling...out of the 100 pools, these were the only ones that were not damaged by construction. The other pools are still functional, however, and do contain the plant being studied. On one end of the site most of the pools were sampled, whereas on the other end of the site only a few pools were sampled. So my second question is: Can I really test for spatial autocorrelation if we do not have any data for the damanged pools? My concern is that we will have a sampled pool with high plant density next to 4 or 5 non-sampled pools...will we get the wrong outcome? I don't know if this makes sense...it's difficult to explain virtually! If anyone has any suggestions I'd really appreciate it! Thanks very much in advance, Sue --- Sue Rodriguez-Pastor Dept. of EPO Biology University of Colorado email address: [EMAIL PROTECTED] --- -- * 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 CH3 | N Nicholas Lewin-Koh / \Dept of Statistics NC C==OProgram in Ecology and Evolutionary Biology || || | Iowa State University || || | Ames, IA 50011 CHC N--CH3 http://www.public.iastate.edu/~nlewin \ / \ /[EMAIL PROTECTED] NC | || Currently CH3 O Graphics Lab School of Computing National University of Singapore The Real Part of Coffee[EMAIL PROTECTED] -- * 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
