Interactive Three-Dimensional Display And Interpretation Of A Complex Physical Model

Abstract Seismic data for a three-dimensional (3-D) marine survey were simulated with a scaled physical modeling system and used to illustrate an interpretational procedure based on a vector refresh graphics system. The physical model included stratigraphic and structural features. A 3-D migration of the raw data formed the main data base for interpretation.Interpretation progressed by displaying seismic sections (vertical and horizontal) on a graphics screen in raster format and drawing interpretational lines using a data tablet controlled cursor in a vector format. The accumulated line drawings were displayed as a rotatable, 3-D drawing from which the three-dimensional aspects of the geologic features could be appreciated. Selected drawings and raster displays were produced in real time on an electrostatic plotter; color prints and high resolution sections were output through the host computer as batch jobs.An important element in the procedure was the number of grey levels used for the displays. Using two grey levels (sign-bit sampling) the whole data volume can be scanned rapidly. Using 64 grey levels each image is full of detail, but the cycle time to a new image is long.IntroductionThis paper describes an interpretational procedure which may have application in three dimensional (3-D) seismic exploration, and illustrates its use with scaled physical model data. The main tool is a vector refresh graphics system with both a vector mode and a raster mode. In its vector mode, it can display 22000 vectors, thirty times a second, and execute orthogonal transformations in real time with a wide range of editing features. Its real time capability to scan through a 3-D data volume in its raster mode and to rotate an interpreted line drawing in its vector mode can be appreciated by an animated movie or video tape.The raster segment generator is capable of displaying on the screen 360 columns by 1024 rows of pixels with 1-bit resolution (or fewer columns with higher resolution). This image can be scrolled vertically or horizontally through a 2-D image of any size in disc storage, and can step through a series of images stored on disc in sequential order at about 24 images per second. With random access files the rate is about 10 images per second. The system allows a large volume to be scanned rapidly with a low resolution display for each image. To accomplish this, the 128 K bit memory boards in the graphics processor are divided in two. Half is used to display the image, and half to store the next image.The vector refresh capability allows an interpreter to overlay 2-D line drawing on each raster display with a data tablet cursor pen, and to merge a series of 2-D drawings into a 3-D drawing. This composite drawing can be rotated, enlarged, fitted with surface meshes, edited and enhanced in various ways. This is done with hardware that applies orthogonal transformations to the coordinates that define the ends of each vector. Thus the digital data base of the line drawing is preserved.The combination of raster and vector capabilities is suitable for interpretation of seismic volumes. For example, successive time slices of a 3-D survey can be displayed in raster format and each slice interpreted by drawing selected contours. The contours are stored as the interpretation proceeds. When the next slice is fetched, the previous contour can be viewed to guide in the selection of the current contour. At any time, all of the interpreted contours can be displayed simultaneously as a three dimensional rotatable drawing. Examples of the results will be discussed below. Hardcopies of any display on the screen can be plotted immediately as electrostatic sign-bit images on paper, and these form the basis for all the data displays found in this paper.