AI-GEOSTATS: Kt estimation variance
Hello ai-geostats list-members Performing an universal kriging on chemical data (log transform of concentration), in some estimation points I obtained an estimation variance larger (in some case three times) than the sill of residual variogram. From what I know this is related to negative weights in the kriging matrix (as I can see looking at the debug file). Now I'm wondering how (if it is possible) I can use this estimation variance. Or better: in which way I can interpret this estimation variance? Thank you in advance for your help... Sebastiano Trevisani Ph. D. student --Geology Departement --Padova University --Italy -- * 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: Kt estimation variance
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 fact(?) and you can derive the answer by simply trying to estimate the value at one point from a single sample at or beyond the range of influence from this location. That is, a weight of +1!! In Universal Kriging, the weights often become negative because the system is trying to force the estimated point to lie on the trend of the samples. Sometimes it can only do this by using negative weights. There is no problem here, unless you have extremely high 'erratic' residuals. In this case, you should probably resolve that problem before trying kriging. If the variance becomes very high in Universal Kriging it is probably because you are extrapolating into sparsely sampled areas. Remember you are trying to estimate the trend as well as the 'residual' value and this contributes to higher variances. You should widen your search radius to include more samples than with Ordinary Kriging. You can see how all this works with our free kriging game. If your data is in Geo-EAS form or a simple CSV file, you can read it into Krigame and see the equations and the solutions. Then vary search parameters etc to see how they are affected. You might want to download our Tutorial 3 which discusses Universal Kriging with the Wolfcamp data. All available at http://geoecosse.bizland.com/softwares with no restriction on use or distribution. Isobel Want to chat instantly with your online friends? Get the FREE Yahoo! Messenger http://mail.messenger.yahoo.co.uk -- * 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: geoR and memory
Isobel, There are published algorithms that will do this - one of the advantages of the UTM projection is that it can be generated anywhere, with the zoning of the projection accounting for the necessary differences around the globe. Good software should be able to deal with UTM zones and hence work anywhere. The disadvantage of UTM is that other commerical mapping (including State) is more likely to use a local grid for the area concerned. It may be possible to find free or shareware that will do the projection - one issue that needs to be addressed though is precision as a lot of the free code is limited in this respect and of course the desired spatial accuracy of subsequent statistical processes needs to be incorporated within this. Otherwise there is often software tailor made for specific countries, e.g., for the UK and Ireland that usually offers a higher precision. It depends on the source data and what you want to do with it - we work to sub-metre precision and this can be a problem. If any of the list need to pursue this further I have a contact who is renowned for his work on co-ordinate transformations in the aerial photography world and who would probably be able to advise. Martin __ ArchaeoPhysica Ltd. Reconnaissance Geophysics for Archaeology Telephone: +44 (0) 7050 369789 E-mail: [EMAIL PROTECTED] Website: http://www.archaeophysica.co.uk __ This e-mail is intended only for the addressee named above and may contain confidential or privileged information. If you receive this e-mail by mistake please advise the sender and destroy it without further disclosure of its content. Unless otherwise stated no opinions expressed in this e-mail should be regarded as representative of any policy of ArchaeoPhysica Ltd. - Original Message - From: Isobel Clark [EMAIL PROTECTED] To: Martin Roseveare [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Sent: Friday, October 24, 2003 4:06 PM Subject: Re: AI-GEOSTATS: geoR and memory Martin - convert your longitude and latitude data into a planar projection first Do you have an algorithm that works everywhere in the world? Isobel http://geoecosse.bizland.com/whatsnew.htm Want to chat instantly with your online friends? Get the FREE Yahoo! Messenger http://mail.messenger.yahoo.co.uk -- * 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: tick sampling
Dear All, I am trying to fiugre out how many locations I need for a sample of ticks in the eastern United States. I know that teh rule of thumb is that that no less than twenty pairs are required per distance class, but is there any other refrence on sampling for spatial analysis? Thank you Russell Barbour Ph.D. Research Associate in Applied Mathematics Vector Ecology Laboratory Yale School of Medicine 60 College St. Rm 600 New Haven CT. 06520 TEL: 203 785 2394 FAX 203 785 3604 email: [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: geoR and memory
On Fri, 24 Oct 2003, [iso-8859-1] Isobel Clark wrote: - convert your longitude and latitude data into a planar projection first Do you have an algorithm that works everywhere in the world? There is no single projection that would be appropriate for everywhere in the world at once, just as there is no 2 dimensional (planar) projection that can accurately preserve angles, distance, direction and area for an entire map:-) Is that what you are asking for? jim b - Jim Bash, Associate DirectorInternet : [EMAIL PROTECTED] CAGIS (m/c 092)Phone (W): 312/996-6367 Program in Geography, Dept of Anthropology Fax : 312/996-6343 University of Illinois at Chicago 1007 W. Harrison St, Rm 2102 BSBURL : http://www.cagis.uic.edu/ Chicago, IL 60607-7138 -- * 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: geoR and memory
On Fri, 24 Oct 2003, Susan King wrote: I would like to have algorithms for converting lat/long into different projections (albers, utm). You might check out http://www.remotesensing.org/proj/ which has source and documentation for PROJ.4, map projection software. I think the source is in C and you would probably have to dig for the algorithms, unless they are in the documentation. Sorry but I haven't looked at PROJ.4 in a long time. I normally refer to a book by John Snyder, Map Projections-- A Working Manual which was published by USGS as USGS Professional Paper 1395 in 1987. But that isn't online and I'm not sure it is available anymore. HTH a little, jim b -- Jim Bash, Associate DirectorInternet : [EMAIL PROTECTED] CAGIS (m/c 092)Phone (W): 312/996-6367 Program in Geography, Dept of Anthropology Fax : 312/996-6343 University of Illinois at Chicago 1007 W. Harrison St, Rm 2102 BSBURL : http://www.cagis.uic.edu/ Chicago, IL 60607-7138 -- * 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: geoR and memory
Hello everyone, Here is a link to Geotrans, a program developed by the US National Imagery and Mapping Agency to convert locations between different coordinate systems. http://earth-info.nima.mil/GandG/geotrans/geotrans.html It can work in batch mode. Julian M. Burgos University of Washington School of Aquatic and Fishery Sciences 1122 NE Boat St. (Box 355020) Seattle, WA 98195-5020 - Original Message - From: Susan King [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Friday, October 24, 2003 12:27 PM Subject: Re: AI-GEOSTATS: geoR and memory I would like to have algorithms for converting lat/long into different projections (albers, utm). Susan L. King Operations Research Analyst USDA Forest Service 11 Campus Blvd., Suite 200 Newtown Square, PA 19073 Phone: (610) 557-4048 Email: [EMAIL PROTECTED] FAX: (610) 557-4250 Isobel Clark [EMAIL PROTECTED] To: Martin Roseveare [EMAIL PROTECTED] ahoo.co.uk cc: [EMAIL PROTECTED] Sent by: Subject: Re: AI-GEOSTATS: geoR and memory ai-geostats-list @unil.ch 10/24/2003 11:06 AM Please respond to Isobel Clark Martin - convert your longitude and latitude data into a planar projection first Do you have an algorithm that works everywhere in the world? Isobel http://geoecosse.bizland.com/whatsnew.htm Want to chat instantly with your online friends? Get the FREE Yahoo! Messenger http://mail.messenger.yahoo.co.uk -- * 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 -- * 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: Kt estimation variance
Dear Isobel Clark Thank you very for your help I have used the software on your web site and I have understood more precisely in which way kriging estimation variance works Sincerely Sebastiano Trevisani -- * 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
