Ursula > 5.5 x 20 metres > Choosing a 5 metres lag, the variance > values are too high in the first 3 -4 lags. This is possibly because you have some competition effect between orchids.
For a square grid, we usually recommend an interval 20% of the grid spacing, so you don't get diagonals lumped in with 'straight' directions. This would suggest that you should try a 1 metre lag, which is probably overkill. The other alternative is to construct directional semi-variograms and specify the correct lag for each direction, to see what differences you get. > My second question is what is the difference between > a variogram and a semivariogram ? As a general rule a "variogram" is a semi-variogram constructed by someone lax in their terminology. No software I know calculates the true variogram (twice the semi-variogram). The correlogram is simply the semi-variogram upside down 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://ecosse.ontheweb.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
