- Dear all,

I have a geological data set and I'd like to compare the

interpolation results from different methods (kriging, minimum

curvature and IDW). I have an "ideal" map from geologists and this

is the map of isolines. The question is, how to compare grids which

comes from interpolation methods and this isolines map? I see two

possibilities here:

1) to compare grids. Then I need to interpolate the isolines map to

grid. And this means, I will possibly get some differences due to

this interpolation., not due to "goodness" (or "badness") of

interpolation method of interest. Another question, what is a

criteria to compare two grids? A mean squared difference? And first

of all, I need an algotithmus to interpolate isolines to grid. I

found a description of such method (it calls "Profiles" in TNTmips or

INTERCON in IRDISI), but descriptions are not detailed enough to

write a code. So, does anyone have such a code (or pointers to that)?

2) another possibility is to compare two sets of isolines, but I have

no idea, how.

If you have ideas about all that, drop a couple of lines, I will

summarise the responses.

Thank you in advance,

Kostantin.

Konstantin Malakhanov, wiss. Mitarbeiter/research engineer

IWW, RWTH Aachen

Tel. 0241-807343

Fax. 0241-8888348

E-Mail: kosta@...-aachen.de

--

*To post a message to the list, send it to ai-geostats@....

*As a general service to list users, please remember to post a summary

of any useful responses to your questions.

*To unsubscribe, send email to majordomo@... with no subject and

"unsubscribe ai-geostats" in the message body.

DO NOT SEND Subscribe/Unsubscribe requests to the list! >The most suitable way to do it is to use the principle of cross

Would it be use an interpolation method to compute a grid, contour the grid

>validation. Given n data points, perform the following for each method:

>1) drop data point i, and use the remaining n-1 data points to provide

>an estimate at the location of the dropped point.

>2) compute the err=y_hat_i - yi,

>where y_hat_i is the estimated value at location i

> y_i is the value of dropped data at location i

>3) repeat steps 1 and 2 at all n points, and compute sum of squared

>error (or the mean square error).

>4) repeat steps 1,2,3 for all methods; then compare the resulting sum of

>squared errors (or the mean square error).

>

>As you notice, we did not have to create a grid. However, the method

>with least errors is the one that will give the best estimation grid in

>terms of this criterion.

>

>Regarding the geologist isoline map, another estimation method, is

>subjective and may or may not be better than the a statistical

>interpolation method. I am not sure if you can use a statistical method

>to judge the adequacy of fit of such a map. However, you can select the

>interpolation method that provides the closest estimate to the isoline

>map. To do so, select as many points as you can on these isolines, and

>consider them data points, then perform cross validation as described

>above. select the interpolation method with the least square error

>score.

>

>Note: I don't recommend the use of grids to solve your problem.

>if you have any further questions, don't hesitate to contact me.

>Alaa

>_________________________________________________________

>A. Ali, Ph.D., P.E.

>New Mexico State Engineer Office

>P.O.Box 25102, Santa Fe, NM 87504

>e-mails: aali@...; or aali@...

>Web: http://www.engineering.usu.edu/Departments/cee/Faculty/ulall/

>Phone: 505-827-6125 Fax: 505-827-6188

>_________________________________________________________

>

using the same levels as the hand-drawn map, and then compare the contours

directly, perhaps by calculating the area between corresponding contours in

each version? We would have to use the map boundaries to close the polygons

formed by the contour line pairs. This would do away with having to grid

the hand-contoured map.

--

*To post a message to the list, send it to ai-geostats@....

*As a general service to list users, please remember to post a summary

of any useful responses to your questions.

*To unsubscribe, send email to majordomo@... with no subject and

"unsubscribe ai-geostats" in the message body.

DO NOT SEND Subscribe/Unsubscribe requests to the list!