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AI-GEOSTATS: Information about Kriging 3D and semivariogram in 3D-list of replies.

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  • lisa pizzol
    Hi to everybody: Regarding my recent question, I received the replies listed below. Thank you very much to all. Lisa My question was: Hello to everybody, I
    Message 1 of 1 , Nov 10, 2003
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      Hi to everybody:



      Regarding my recent question, I received the replies listed below. Thank you very much to all.

      Lisa



      My question was:





      Hello to everybody,







      I have to build a semivariogram in 3D

      and I need to know if I can use the same concepts

      used for the 2D semivariogram or if the theory is

      different. For example how can I consider the

      distance? In one article they said that I can first

      build the semivariogram in the horizontal direction

      in order to find the values of sill, range, nugget

      and the equation of the semivariogram. After this I

      can use these information to find the range in the

      vertical direction. Do you know any references that

      explain exactly how to do it?



      Thank you very much.





      Lisa



      Replies:



      Lisa



      Distances and directions in 3d can be calculated very

      simply just as in 2d. There is shareware (Geostat

      Toolbox) and other software out there for 3d.



      Calculating semi-variograms whilst pretending your

      data is two dimensional can lead to extremely

      misleading semi-variograms. In particular your nugget

      effect will be exaggerated out of all proportion to

      reality.



      At the risk of offending some of our more sensitive

      list members, can I suggest you try things out on our

      FREE teaching software PG2000 which includes 3d

      capabilities. Test data set for this is a copper dump,

      which is provided in the FREE downloadable data sets.

      Find all this and other free goodies at

      http://geoecosse.bizland.com/softwares



      Isobel Clark

      _____________





      have a look on Isaaks and Srivastava (applied geostatistics) book



      you will find there a good explanation on variogram modelling





      cheers

      _________________



      Hi Lisa



      You can apply exactly the same principles in 3d that you use in 2d.

      Variograms are functions to measure variability of samples by pairs using the variance as an index.

      In mineral deposits what we do? We use a variogram down the hole, do define the nugget effect, that is a residual variance that you must start you variogram and must be calculated in the shortest distance that you have, after that we calculate 3 variograms to represent 3d, if you is a geologist like me, the directions are basically the azimuth, the dip and the vertical direction for the plane given by azimuth and dip.



      Good references:



      Basic Linear Geostatistics, 1998, Armstrong, M.

      Introduction to Applied Geostatistics, 1989, Isaaks & Srivastava

      GSLib, 1990 Deutsch & Journel



      Best Regards



      Ciao (io no parlo italiano, io voglio parlare un dia...)



      Alessandro



      ________________



      Ciao lisa

      La teoria per costruire un variogramma tridimensionale e` la stessa. Se vuoi individuare rapidamente gli assi di anisotropia del modello

      la cosa migliore, se hai molti dati, e` quella di studiare il variogramma di volume (il corispettivo del variogramma di superficie in due dimensioni). Comunque dipende dalla geometria di campionamento. Se non hai la possibilita` di calcolare il variogramma di volume studia il variogramma lungo diverse direzioni ed inclinazioni. Spesso si puo` studiare il variogramma solo lungo il piano e lungo la verticale. IN questo caso sei costretta ad ammettere che gli assi di anisotropia sono orientati secondo gli assi cartesiani. Ti consiglio Gstat o Gslib come software free o Isatis a pagamento. Quello che dice l'articolo non mi sembra chiaro.....a volte si fa il contrario.

      Ciao

      Sebastiano

      Universita` Padova



      ____________



      Hello Lisa:



      Attached you can find some page write in Spanish (I hope you understand this language), in which I explain to my students the construction of the semivariograms in 2D and 3D. Be careful with the line intermittent in the last paragraph.



      I hope this help you.



      Best regards



      José Quintín



      _________



      You can use GSLIB it's also a free soft. You can find it in ai-geostats

      web page. In the corresponding book you can also find the theoretical

      basis of it.

      Carme



      _________



      Hi Lisa,



      I would recommend that you look at Chapter 16 of Isaaks and

      Srivastava's

      book "An introduction to Applied Geostatistics" which offers a very

      nice

      description of how to model semivariograms in different directions and

      up to 3 dimensions. You can also refer to the following paper:

      Barabas, N., Goovaerts, P. and P. Adriaens. 2001. Geostatistical

      assessment and validation of uncertainty for three-dimensional dioxin

      data

      from sediments in an estuarine river. Environmental Science &

      Technology,

      35(16): 3294-3301.



      Best regards,



      Pierre Goovaerts



      ____________



      Hi Lisa,



      I am studying on geostatistical 3D data, too. I am a mining engineer. I am using it in reservoir modelling. I searched material about it so much. but the information about that is very limited. Practically there are two semi-variogram plane: 1 horizontal, 2 is vertical and independent from each other. I have found a 3D variogram modelling software called "snowden" at www.sonwdentec.com.au . But I could not use the software. There are some applications at there. Have you got any material (paper, book etc.) about 3D variogram?



      I guess It helps you a little.



      Good Day.



      Tayfun



      ______________




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