On Thursday, December 6, 2001, at 04:12 AM, Michael Dennis wrote: > > I don't think this is right but if you can explain to me how the Drift > is > actually applied in laymans terms it would be greatly appreciated. Also > when you do kriging with external drift do you have to model a > variogram or > can a reasonable one be computed automatically, if so how would you > compute > it?
Kriging with an external drift is just an extension of universal kriging. UK assumes that one knows the shape of the trend but not its magnitude (or coefficients). For example a linear drift could be modeled by Mean = a + bX + cY where X and Y are the coordinates of the data. And so on and so forth for higher order polynomial trends. In KED, the trend shape is not defined analytically; rather, it is assumed that it is defined explicitly at all locations based on some densely sampled secondary variable. However, such a secondary variable must be smoothly varying in space, and also it must be available at all locations of the primary data and the locations being estimated. As in UK, the magnitude of the trend is unimportant, it is the shape that we're interested in. An external drift that varies linearly with X and Y would be equivalent to UK with an analytical trend of the same order polynomial, i.e. 1. Regards, Syed Maersk Copenhagen -- * 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
