uhuy mas oki emang top.. thx buat pencerahannya.. Joseph
----- Original Message ---- From: oki musakti <[EMAIL PROTECTED]> To: iagi-net@iagi.or.id Sent: Wednesday, July 25, 2007 7:43:09 AM Subject: [iagi-net-l] Gridding Algorithm Re: [iagi-net-l] Tentang Minscape... :-) Pada dasarnya gridding adalah proses penyebaran (populating) regularly spaced Z value from irregularly spaced XYZ point (or 'line'). Dengan kata lain menyebarkan data 0D (point, misalnya well derived depth ) atau '1D' (lines, misalnya seismic line, mineral content along wellbore --> bisa juga argue bahwa data di line adalah kumpulan point, walhasil 0D juga) menjadi 2D (map grid). Saya ingat belasan tahun lalu ikut kursus sandstone depositional environment nya Dan Busch. Ba'da salah satu excercisenya yaitu membuat kontur netsand map beliau bilang yang intinya ' If you use the computer as a blackbox to do your contouring, then most likely the result will not be worth the paper it is printed on. The BEST WAY TO CONTOUR IS TO USE YOUR HEAD AND YOUR HAND'. So, kembali ke pertanyaan algoithma grid mana yang sebaiknya dipakai ?, jawabannya adalah yang bisa memberikan hasil paling mendekati prekonsepsi (model) geologi dikepala kita. Seperti yang Noel bilang, ini akan banyak tergantung dari faktor2 seperti jumlah dan distribusi data dll. Sebagai rule of thumb, saya kutip deskripsi singkat beberapa algoritma popular yang banyak dipakai. Artikel lengkapnya ada di http://www.seismo.unr.edu/ftp/pub/louie/class/333/contour/surfer.html Cheers Oki Inverse Distance is fast but has the tendency to generate "bull's-eye" patterns of concentric contours around the data points. Kriging is one of the more flexible methods and is useful for gridding almost any type of data set. With most data sets, Kriging with a linear variogram is quite effective. In general this is the method that we would most often recommend. Kriging is the default gridding method because it generates the best overall interpretation of most data sets. For larger data sets, however, Kriging can be rather slow. Minimum Curvature generates smooth surfaces and is fast for most data sets. Nearest Neighbor is useful for converting regularly spaced XYZ data files to Surfer grid files. Or when your data is a nearly complete grid with only some missing holes, this method is useful for filling in the holes, or creating a grid file with the blanking value assigned to those locations where no data is present. Polynomial Regression processes the data so that underlying large scale trends and patterns are shown. This is used for trend surface analysis. Polynomial Regression is very fast for ny amount of data, but local details in the data are lost in the generated grid. * Radial Basis Functions is quite flexible, and like Kriging, generates among the best overall interpretations of most data sets. This method produces results that are quite similar to Kriging. Shepard's Method is similar to Inverse Distance but does not tend to generate "bull's eye" patterns, especially when a Smoothing factor is used. Triangulation with Linear Interpolation is fast with all data sets. When you use small data sets Triangulation generates distinct triangular facets between data points. One advantage of triangulation is that, with enough data, triangulation can preserve break lines defined in a data file. For example, if a fault is delimited by enough data points on both sides of the fault line, the grid generated by triangulation will show the discontinuity. Noel Pranoto <[EMAIL PROTECTED]> wrote: Tepatnya resource modelling Pak Djuharlan, hex3. Pak Wahyudi, saya coba jawab sebisanya. Jawaban cepat pertanyaan Anda adl dengan grid (2D). Sebagai tambahan, resource modeling, apapun peranti lunak dan komoditas bahan galiannya, umumnya memperhatikan 3 hal berikut: 1. Algoritma (trend surface, kriging dan min curvature) 2. Data (jumlah data, pattern dan orientasinya) 3. Area pencarian (luasan, bentuk, orientasi, pembobotan/weighting) 4. Ukuran grid (ukuran cell, bentuk, orientasi) Saran saya sebelum memulai pemodelan, pelajari saja dulu datanya sehubungan dgn poin2 di atas dan tools yg hrs digunakan sdh barang tentu geostatistik (spt yg dibilang Pak Djuharlan). Geostatistik adl alat/tools utk menentukan parameter2 yg digunakan dalam pemodelan di atas, misalnya apa algoritma yang cocok dipakai utk jumlah, pola dan data eksplorasi yg Anda punya, berapa besar ukuran dan bentuk grid yang optimum, dll. Untuk statistik deskriptif dari data yang Anda punya spt distribusi, rata2 aritmetik, histogram, sd, outliers, dll bisa pakai Excel saja tapi utk variogram setahu saya yg gratisan dan mudah digunakan cuma Variowin (googling saja, pasti ketemu). Kalau tdk salah di thn 2000 ada buku yang bagus dan praktis ttg hal ini, judul lengkapnya: Understanding Contouring: A Practical Guide to Spatial Estimation Using a Computer and Variogram Interpretation oleh Krajewski & Gibbs. Di dalamnya malah dilampirkan contoh-contoh "pseudo-features" kontur yg dihasilkan dari dataset yg sama namun menggunakan berbagai jenis metoda pemodelan. Ini berguna sekali utk novice resource modeller yg kadang bingung jika ketemu "bulls-eye": ini bener2 anomali atau salah memodel? Sayangnya punya saya sendiri sdh entah kemana nasibnya karena keseringan pindah-pindah tapi mungkin masih bisa Anda beli lewat Amazon. Dalam buku itu pengarangnya ada menulis demikian: "Explorationist conceive mineral deposits and contours in their minds and draw them with a hand guided by experience, data and aesthetics. Someday, computers will be programmed to do as well (Krajewski, 1984)." Semoga berguna dan silakan jika ada koreksi/tambahan. Salam, Noel On 25/07/07, [EMAIL PROTECTED] wrote: > > > > > Nah tuh, bahas lho masalah geostatistik ….. (kalau nggak salah). > > > > > Regards/Salam, > > Md. Johaness Djuharlan - 003185 > PT Freeport Indonesia > Tembagapura 99930 > > "Keep Smile, makes your life easier" > "Mangan ora mangan kumpul, kumpul karo mangan-mangan". > Disclaimer: This email (including any attachments to it) is confidential, > used for internal PTFI only. > > ________________________________ > > > From: W. Adhiutomo [mailto:[EMAIL PROTECTED] > Sent: Tuesday, July 24, 2007 10:54 PM > To: iagi-net@iagi.or.id > Subject: [iagi-net-l] Tentang Minscape... :-) > > > > > > Salam, > > > > > > Bapak-bapak, Ibu-ibu... > > > Ada yang familiar dengan MIncom?? Aku mau nanya... Surface yang paling bagus > untuk modeling geology apa ya?? Surface expression, grid, atau triangle... > :-) Thanks. > > -- > Regard, > Wahyudi Adhiutomo > Mobile: +62852 487 33499 > Email: [EMAIL PROTECTED] > > ----- > This email (including any attachments to it) is confidential and is sent > for the personal attention of the intended recipient only and may contain > information that is privileded, confidential or exempt from disclosure. If > you have received this email in error, please advise us immediately and > delete it. You are notified that using, disclosing, copying, distributing or > taking any action in reliance on the contents of this information is > strictly prohibited. > ----- ---------------------------------------------------------------------------- Hot News!!! 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