Re: AI-GEOSTATS: Choosing Lag Distance and Angular Tolerance
--- Lucie Vallée <[EMAIL PROTECTED]> wrote: > > > Could you explain what you mean by "nearest > neighbour distances between samples locations"? This is something I learned about in quantitative ecology in the 1960's ;-) You take each sample in turn and find the sample closest to it. Note the distance. A histogram of the distances will give you a sort of natural inter-sample distance for use in the semi-variogram calculation. The histogram can also be used to check whether sampling is randon, uniform, clustered etc. I don't have a full reference but it should be easy to find: Pielou, Cressie or any other book with Spatial Statistics in the title. 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
Re: AI-GEOSTATS: Choosing Lag Distance and Angular Tolerance
Andrew You can apply 'standard' geostatistics if the measurements are the 'average' (or some similar feature) over an area. It makes interpeting the semi-variogram extremely tricky if you combine many different sizes of sample, but common sense is the main thing here. The trick is to derive a point semi-variogram model from which any size can be derived (see Chapter 3, Practical Geostatistics 1979, downloadable free from Web, http://uk.geocities.com/drisobelclark/practica.html) Kriging is modified to reflect that the samples are averages, mainly by changing the diagonal elements 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 to > bring it up. Will > variograming and other such techniques work for the > data the previous writer > described, e.g samples aren't at points, but areas > (and areas that might > have very little to do with the question). If they > did use points in the > calculations where would the points be placed, at > the center of the county, > at the major population center, at some arbitrary > point (e.g most northerly > point). > > I may be miss reading the description, perhaps the > sample are point samples, > but were taken with one sample in each county. > > Obviously the point samples are never really point > sample, they must be > taken over some area, approximating a point, but > does this design seem to > push the boundaries on that assumption. > > Andrew > - Original Message - > From: "Yadollah Waghei" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Cc: <[EMAIL PROTECTED]>; > <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; > <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; > <[EMAIL PROTECTED]> > Sent: Tuesday, May 15, 2001 7:33 AM > Subject: AI-GEOSTATS: Choosing Lag Distance and > Angular Tolerance > > > > Hello dears > > I have a spatial data set contaning n=262 > observarion (The variable of > interest is Rate of Tuberculosis in 262 counties of > Iran). I want to fit > some models to Directional semi-variograms,and then > build anisotropic > semi-variogram. > > Then questions are > > - Is there any rule for choosing Lag Distance and > Angular Tolerance? > > -Also,how we can balance between Lag Distance and > Angular Tolerance? > > -Do you agree that both must be very small,as > possible?(Such that number > of pairs in each lag>20, for example) > > > > Thank you > > Yadollah Waghei > > Dep.of Biostatistics > > Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111 > > Tel:8011001-3872 Fax:8007989 > > > ___ > > Visit http://www.visto.com/info, your free > web-based communications > center. > > Visto.com. Life on the Dot. > > > > > > -- > > * 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 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
Re: AI-GEOSTATS: Choosing Lag Distance and Angular Tolerance
I have a question relating to this question, certainly not to question the previous writer, it just seems like a good time to bring it up. Will variograming and other such techniques work for the data the previous writer described, e.g samples aren't at points, but areas (and areas that might have very little to do with the question). If they did use points in the calculations where would the points be placed, at the center of the county, at the major population center, at some arbitrary point (e.g most northerly point). I may be miss reading the description, perhaps the sample are point samples, but were taken with one sample in each county. Obviously the point samples are never really point sample, they must be taken over some area, approximating a point, but does this design seem to push the boundaries on that assumption. Andrew - Original Message - From: "Yadollah Waghei" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Tuesday, May 15, 2001 7:33 AM Subject: AI-GEOSTATS: Choosing Lag Distance and Angular Tolerance > Hello dears > I have a spatial data set contaning n=262 observarion (The variable of interest is Rate of Tuberculosis in 262 counties of Iran). I want to fit some models to Directional semi-variograms,and then build anisotropic semi-variogram. > Then questions are > - Is there any rule for choosing Lag Distance and Angular Tolerance? > -Also,how we can balance between Lag Distance and Angular Tolerance? > -Do you agree that both must be very small,as possible?(Such that number of pairs in each lag>20, for example) > > Thank you > Yadollah Waghei > Dep.of Biostatistics > Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111 > Tel:8011001-3872 Fax:8007989 > ___ > Visit http://www.visto.com/info, your free web-based communications center. > Visto.com. Life on the Dot. > > > -- > * 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: Choosing Lag Distance and Angular Tolerance
Think of it as focussing a camera. You are looking for the clearest picture. There will be a certain lag (in each direction) at which the calculation will balance between detail on distance, detail on angles and number of pairs. In general: # the more anisotropic the structure, the smaller the tolerance on angle should be # a natural interval can be found from the 'nearest neighbour' distances between sample locations # you won't hit it on the first shot! 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 -- * 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: Choosing Lag Distance and Angular Tolerance
Hello dears I have a spatial data set contaning n=262 observarion (The variable of interest is Rate of Tuberculosis in 262 counties of Iran). I want to fit some models to Directional semi-variograms,and then build anisotropic semi-variogram. Then questions are - Is there any rule for choosing Lag Distance and Angular Tolerance? -Also,how we can balance between Lag Distance and Angular Tolerance? -Do you agree that both must be very small,as possible?(Such that number of pairs in each lag>20, for example) Thank you Yadollah Waghei Dep.of Biostatistics Tarbiat Modarres Univ.(Tehran)Po.Box: 14115-111 Tel:8011001-3872 Fax:8007989 ___ Visit http://www.visto.com/info, your free web-based communications center. Visto.com. Life on the Dot. -- * 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
