Patent Publication Number: US-6665117-B2

Title: Method and apparatus for interactive curved surface borehole interpretation and visualization

Description:
This application is a continuation-in-part of application Ser. No. 09/698,678, filed Oct. 27, 2000, which is a continuation-in-part of application Ser. No. 09/306,611, filed May 6, 1999, now U.S. Pat. No. 6,215,499 B1, issued Apr. 10, 2001, and application Ser. No. 09/306,612, filed May 6, 1999, now U.S. Pat. No. 6,188,517 B1, issued Feb. 13, 2001. 
    
    
     This invention relates to a method and apparatus for projecting spatially correct seismic data or wellbore data onto a large three-dimensional (3D) curved display surface, to aid in interpretation of geological characteristics of the earth. More specifically, this invention relates to a method for projecting computer graphic video images of seismic data or wellbore data onto a large curved 3D display surface, allowing viewers to interact with the 3D display, and to use their peripheral vision, and thus perceive the displayed imagery with a sense of realism comparable with natural viewing of a 3D physical reality. 
     BACKGROUND OF THE INVENTION 
     For many years seismic exploration for oil and gas has involved the use of a source of seismic energy and its reception by an array of seismic detectors, generally referred to as geophones. When used on land, the source of seismic energy can be a high explosive charge electrically detonated in a borehole located at a selected point on the terrain, or another energy source having capacity for delivering a series of impacts or mechanical vibrations to the earth&#39;s surface. Offshore, air gun sources and hydrophone receivers are commonly used. The acoustic waves generated in the earth by these sources are reflected back from strata boundary and/or other discontinuities and reach the earth&#39;s surface at varying intervals of time, depending on the distance traversed and the characteristics of the subsurface traversed. On land these returning waves are detected by the geophones, which function to transduce such acoustic waves into representative electrical analog signals, which are generally referred to as traces. In use on land an array of geophones is generally laid out along a grid covering an area of interest to form a group of spaced apart observation stations within a desired locality to enable construction of three-dimensional views of reflector positions over wide areas. The source, which is offset a desired distance from the geophones, injects acoustic signals into the earth, and the detected signals at each geophone in the array are recorded for later processing using digital computers, where the analog data is generally quantized as digital sample points, e.g., one sample every two milliseconds, such that each sample point may be operated on individually. The geophone array is then moved to a new position and the process is repeated to obtain a 3D data volume for a seismic survey. 
     After exploration of an area is completed, data relating to energy detected at a plurality of geophones will have been recorded, where the geophones are located at varying distances from the shotpoint. The data is then reorganized to collect traces from data transmitted at various shotpoints and recorded at various geophone locations, where the traces are grouped such that the reflections can be assumed to have been reflected from a particular point within the earth, i.e., a common midpoint. The individual records or “traces” are then corrected for the differing distance the seismic energy travels through the earth from the corresponding shotpoints, to the common midpoint, and upwardly to the various geophones. This step includes correction for the varying velocities through rock layers of different types and changes in the source and receiver depths. The correction for the varying spacing of shotpoint/geophone pairs is referred to as “normal move out.” After this is done, the group of signals from the various midpoints are summed. Because the seismic signals are of a sinusoidal nature, the summation process serves to reduce noise in the seismic record, and thus increasing its signal-to-noise ratio. This process is referred to as the “stacking” of common midpoint data, and is well known to those skilled in the art. Accordingly, seismic field data undergoes the above-mentioned corrections, and may also undergo migration, which is an operation on uninterpreted data and involves rearranging of seismic information so that dipping horizons are plotted in their true location. Other more exotic known processing techniques may also be applied, which for example enhance faults and stratigraphic features or some other attribute, before the continuously recorded traces are reduced to vertical or horizontal cross sections or horizontal map views which approximate subsurface structure, and are usually in color. 
     Once the seismic data is satisfactorily processed to incorporate necessary corrections and desired enhancements, the geophysicist interprets the 3D seismic information. In general terms, interpretation involves deriving a simple plausible geological subterranean model that is compatible with the observed data. This model is never unique, and discovering it involves a sequence of somewhat arbitrary choices. 
     Despite significant progress in interactive 3D seismic interpretation systems, seismic workstations continue to rely on vertically and horizontally displayed planar slices of recorded data to provide almost all of the “working surfaces” for horizon and fault picking, and correlation. These planar slices provide only a limited perspective of the full three dimensional picture. Often animation of successive slices is required to provide information about the third dimension. However, animation intrinsically forces a three-dimensional interpretation based on the interpreter&#39;s memory of the changing picture through time, rather than on direct comparison and correlation of the data. 
     In observing and interpreting the seismic information displaying in a useful form is highly advantageous. Display systems are widely used in diverse image display applications, with most systems employing either planar or substantially planar display surfaces, i.e., flat wall screens which have an inherently limited field of view. While it is possible to extend the observers field of view by simply increasing the vertical and horizontal dimensions of the planar display screen, this expansion generally results in an unacceptable level of distortion of the image. In order to permit users to view objects peripherally, display technology has been developed which generally uses multiple projectors to project adjoining images on adjacent sections of a large wraparound screen so that observers can view objects with depth perception in 3D space. 
     Accordingly, four screen types are commonly used today to facilitate the many diverse image display applications. These four screen types are: 1) a flat wall, 2) multiple adjacent flat walls, 3) a dome, and 4) a curved wraparound panel, which can be semi-toroidal. All of these display surfaces can include stereo 3D graphics, and some applications require it to be successful. 
     The reason that no one screen type has persisted is that the different problems and purposes encountered with display systems are best individually addressed by only one of the various screen types mentioned above. 
     Another tool used in the exploration and production of oil and gas, sometimes in conjunction with seismic data imaging, is borehole imaging. After an oil or gas borehole has been drilled into the earth, it is of interest to the geologist to study the image, texture, composition and orientation of the formations that make up the borehole. Numerous borehole tools exist that provide images of strata or conditions in a borehole. These tools are based upon electrical, radioactive, acoustic and video imaging technology. The measurements of these tools represent a circular or cylindrical pattern that covers 360 degrees of the wellbore for up to hundreds of feet in depth with resolution to fractional inches. Current display and interpretation technology is inadequate or cumbersome because the images are shown on flat computer screens or flat paper sections. Discussions of these tools as well as display systems for viewing the images are illustrated by U.S. Pat. No. 4,740,930, entitled “Surface Processing and Display of Borehole Televiewer Signals”, issued Apr. 26, 1988, in the name of Robert A. Broding; U.S. Pat. No. 4,847,814, entitled “Three-Dimensional Borehole Televiewer Display”, issued Jul. 11, 1989, in the name if Jorg A. Angehm; and U.S. Pat. No. 5,502,686, entitled “Method and Apparatus for Imaging a Borehole Sidewall”, issued Mar. 26, 1996, in the name of Efraim Dory et al. As these patents illustrate, flat screens and/or paper have been traditionally used for displaying borehole images. Such flat images are hard to interpret and understand because they are presented in an abstract format that does not resemble the cylindrical surface from which they were extracted. Interpretation of structural or stratigraphic elements requires drawing sinusoidal curves on the flat images and then having the computer program convert these lines into plans of data that represent the dip and azimuth of the feature in question. 
     Accordingly, it is an object of this invention to provide a hybrid screen that combines the four screen types in a unitary structure. 
     A more specific object is to provide a hybrid screen for viewing various 3D combinations of wraparound, dome, flat wall and multi-wall type displays using a single video projector or multiple video projectors. 
     A still more specific object of this invention is to provide a portable, self-supporting rigid structure with a concave inner viewing surface, which is suitable for positioning on a desktop or on a moveable support table. 
     Yet another object is to provide an economical viewing surface that gives the viewer a sense of depth perception without requiring stereo projection and stereo glasses. 
     It is still another object of this invention to create a truly three-dimensional interactive graphic workstation to aid in geological interpretation of seismic data. 
     A more specific object of this invention is to visualize spatially correct seismic data on a large concave screen that facilitates horizon and fault mapping of seismic data. 
     Still another object is to provide a projection system for computer graphic images of seismic data that includes a portable self-supporting rigid screen with a concave inner display surface, which is economical in cost, and includes about fifty times more viewing area compared to conventional seismic workstation monitors. 
     Another more specific object of this invention is to provide a desk-top-based projection system having a concave screen, and a projector located about nine feet in front of the curved screen for use in interactive desk top viewing environments. 
     A further object is to provide a projection display system which can be used to view large scale monoscopic as well as stereoscopic color imagery of three-dimensional seismic data. 
     Still a further object is to provide a method for displaying wellbore data which provides a more natural and intuitive means to display the data. 
     SUMMARY OF THE INVENTION 
     While the invention below is described in terms of mapping and projected 3D seismic data, it should be understood that the techniques described herein can be adapted to mapping and projecting 3D data in other fields, such as medical displays, video games and scientific 3D viewing. Accordingly, the invention claimed below should not be construed as limited for use with 3D seismic data. 
     According to the present invention the foregoing and other objects and advantages are attained in a method and apparatus for extracting, mapping and projecting 3D seismic data to its spatially correct location on a relatively large concave 3D display surface. The method is based on computer software, and involves storing a volume of digitally formatted seismic data in memory of a suitable computer as a first step. A mathematical model is then created corresponding to the shape of the concave 3D display surface, and the mathematical model is inserted in the computer memory so as to at least partially intersect the seismic data volume. The intersecting seismic data is extracted and mapped onto an image plane. Next, the extracted data is processed using digital computational techniques so as to maintain correct spatial position for the varying projector to screen distances associated with the concave 3D display surface, and is then projected onto the concave display surface in its spatially correct dimensions. This means that the displayed seismic data is not a vertical slice of seismic data projected onto a curved screen, but is data carved out of the 3D data volume corresponding to the shape of the concave display surface. 
     Accordingly, the apparatus of this invention includes a relatively large 3D display surface compared to a typical CRT monitor screen, and which is suitable for positioning on a desk or tabletop. The presently preferred display surface is a multi-section hybrid projection screen structure having a concave display surface for viewing video images. This presently preferred 3D display surface facilitates viewing on four commonly used screen types including: a flat wall, multiple adjacent flat walls, a concave semidome, and a semi-cylindrical wraparound screen. The various screen types are combined into a single screen referred to herein as a “hybrid” screen, which includes three sections, i.e., a ceiling section which is a concave semidome extending 180 degrees horizontally, and 90 degrees vertically, a semi-cylindrical lower screen panel, and a flat semicircular floor section. The semidome is elevated above the desktop supported by the cylindrical lower section which is edgewise connected to the semidome. The semicircular floor area completes the display surface. A video projector for displaying the seismic data, which allows the high speed graphic output of a computer system to be projected, enlarged and focused onto a concave screen, is located at a convenient distance from the display surface. Accordingly, computer generated signals control the view to be displayed, and the views include animation of successive images derived from the volume of data to display spatially correct seismic information throughout the data volume. 
     Also connected to the computer, or parallel computers as the case may be, can be a keyboard, a mouse, two CRT seismic workstation monitors and a relatively small flat auxiliary screen in the shape of a paddle, that can be held by the geophysicist and positioned within the volume inside of the larger concave display. 
     In a preferred embodiment, the 3D display surface is a unitary construction that combines viewing features of the four commonly used screen types including: a flat wall, multiple adjacent walls, a semidome, and a wraparound. Accordingly, the display surface includes multiple sections for viewing 3D displays. Various combinations of these sections may also be used for viewing, such as the semidome ceiling section together with the flat wall, and, further, the various sections can be divided into subsections or subareas for detailed viewing. 
     In use, a video projector, which accepts multiple simultaneous inputs, is connected to a computer to allow the graphic output of the computer to be projected, enlarged, and focused onto the hybrid screen. Accordingly, computer generated signals control the view to be displayed, and the views include section or subsection displays, as well as animation of successive views, which imparts lifelike motion to an object and which is derived from the volume of data, to display information from throughout the data volume. 
     In another preferred embodiment, a relatively small flat auxiliary screen in the shape of a paddle is provided. This paddle screen can be held by the viewer and positioned within the volume inside of the hybrid screen. An electromagnetic transmitter mounted on the outside of the concave screen surface in combination with a receiver mounted on the paddle screen detect the position and orientation of the moveable paddle throughout the space defined within the hybrid screen, and an interactive image is displayed on the paddle, representing the data that exists at the detected spatial position. Thus, the paddle can be used for exploring the volume within the hybrid screen. In simulation displays, the image on the paddle could represent a view corresponding to a rear view mirror. Further, in mining or seismic displays, the paddle can display petrophysical properties of rocks or acoustic waves that are present at that relative position in the interior of the concave display surface. 
     The method and apparatus of this invention using a large 3D display surface, thus can display a variety of useful views, which are helpful in picking or interpreting seismic horizons and fault segments observed on the surface of the hybrid screen. These views include: 1) a wraparound 180-degree display using only the semi-cylindrical lower portion of the screen, 2) a 180-degree by 90-degree dome display using the semidome ceiling only, 3) a 180-degree wraparound plus floor display using the combination of the semi-cylindrical lower screen panel and the floor, 4) a single wall or a three-wall display using the semi-cylindrical lower screen panel divided into three subareas, 5) a single wall plus floor using the combination of a subarea of the semi-cylindrical lower screen panel and the floor, and 6) a silo with a floor, where the entire concave display surface is illuminated. In addition, the software incorporates real-time navigation through a data volume, and facilitates interactive features including: translate, zoom and rotate. This provides the user with full flexibility to explore the entire data volume, and simplifies quick interactive reconnaissance viewing of the 3D seismic data volume from a variety of viewpoints. 
     According to a further embodiment, a method and apparatus for extracting, mapping and projecting wellbore images to its spatially correct location on a relatively large concave 3D display surface is provided. The method comprises storing a set of borehole data in the memory of a computer; creating a mathematical model for a concave display surface in the memory wherein the mathematical model at least partially intersects the set of borehole data in the memory; extracting borehole data from the set of borehole data intersecting the mathematical model and projecting the extracted data onto a concave display surface to produce a computer graphic image of spatially correct borehole data. 
     Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description and the drawings, wherein there is shown and described some of the several preferred embodiments of the invention. While the best mode contemplated for carrying out the invention is illustrated as applied to a particularly shaped concave 3D display surface, it will be realized that the invention is suitable for other and different embodiments such as projecting the spatially correct seismic surfaces, spatially correct borehole surfaces or any other data formatted as a 3D digital volume, onto any desired shaped surface, such as the interior of a hemispherical display surface, the outer surface of a sphere, a corner between walls or a flexible screen curved to a desired shape. Also several details of the invention are subject to modification in various obvious respects, all without departing from the invention. Accordingly, the description of the invention and the drawings are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic elevation side view of a video projection system located in an average sized domestic room, showing the full projection ray viewing volume according to this invention. 
     FIG. 2 is a schematic plan view of the video projection system located in the room illustrated in FIG. 1, and showing an arrangement of computer, projector and related digital equipment. 
     FIG. 3 is a perspective view of the hybrid screen. 
     FIG. 4 is a schematic view of the auxiliary paddle screen. 
     FIGS.  5 ( a )- 5 ( b ) are schematic views showing alternative embodiments of the auxiliary paddle screen. 
     FIG. 6 is a perspective view of the hybrid screen with the auxiliary paddle screen in use. 
     FIGS.  7 ( a )- 7 ( b ) are plan views showing top and lower horizontal support members respectively for the semidome of the hybrid screen. 
     FIG.  7 ( c ) is a front elevation of the lower screen panel. 
     FIG. 8 is a simplified computer flow diagram showing the major steps of the method for displaying spatially correct seismic data according to this invention. 
     FIG. 9 is a computer flow diagram showing steps for extracting data intersecting the display surface from the 3D seismic data volume. 
     FIG. 10 is a computer flow diagram showing steps for mapping extracted seismic data onto an image plane assumed to be located in the ray projection volume between the projector and hybrid screen. 
     FIG. 11 is a detailed block diagram showing the overall organization of data input and processing steps for displaying spatially correct 3D seismic data on a concave display device according to this invention. 
     FIG. 12 is a simplified computer flow diagram showing the major steps of the method for displaying spatially correct borehole data according to an embodiment of this invention. 
     FIG. 13 is a computer flow diagram showing steps for extracting data intersecting the display surface from the 2D borehole data array. 
     FIG. 14 is a computer flow diagram showing steps for mapping extracted borehole data and then displaying the mapped data. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     Referring first to FIGS.  1  through  7 ( c ), the illustrated projection display system of the present invention will be described in greater detail hereinbelow. In general, the present projection display system can be used to display images carved out of digital formatted data volumes, whether the data is real, synthetic, or part real and part synthetic, and has obvious utility to many industrial applications in addition to seismic visualization and interpretation, including but not limited to: 
     1) manufacturing design reviews, 
     2) ergonomic simulation, 
     3) safety and training, 
     4) video games, 
     5) cinematography, 
     6) scientific 3D viewing, and 
     7) medical displays. 
     The invention, however, will be illustrated with reference to projecting seismic data on a hybrid screen. Suitable computer software techniques for generating seismic displays of spatially correct dimensions on a large 3D display surface, and for driving a video projector with computer generated signals will be more fully explained hereinafter. 
     As best shown in FIGS. 1 and 2, the projection display system has several major components, i.e.: a 3D structure for displaying images generally indicated at  20 , and referred to herein as a hybrid screen, one or more image projectors  32  for projecting color images onto the hybrid screen, and an associated computer system generally shown at  34  for generating video images. 
     The presently preferred hybrid screen  20  is of compact unitary construction having three sections forming a generally concave display surface, the sections include: a concave semidome ceiling section  30 ; a semi-cylindrical lower section  22 , and a flat semicircular floor section  25 . The cylindrical screen section  22 , which is also illustrated in FIG.  7 ( c ), is edgewise mounted to a lower edge of the semidome  30 . Projection rays illustrated by lines  23  indicate the limits of the viewing volume of the full screen  20 . It is noted, however, that the viewing volume may be adjusted to illuminate only desired sections or subareas of the full screen. The concave display surface of the hybrid screen  20  is generally indicated at  24 , and includes the semidome section  30 , which is elevated above the desk  28  by edgewise mounting on the semi-cylindrical screen section  22 . Also as illustrated in FIG. 2 the cylindrical screen section  22  includes left, central and right subarea display surfaces  26 A,  26 B and  26 C respectively, such that three independent wall views can be simultaneously displayed on the three designated subareas. Still referring to FIGS. 1 and 2, the lower edge of the semi-cylindrical display screen  22  is attached to flat semicircular floor section  25 ; thus, supporting the semidome section above the desk  28 . 
     Any suitable material for receiving an image can be used for the construction of the hybrid screen. Readily available materials such as wood, foam board, fiberglass or molded plastic are presently preferred for the construction of the hybrid screen. In the illustrated preferred embodiment, the size of the hybrid screen with reference to the letters A and B in FIG. 1; C, D, and E in FIG. 3; F and G in FIG.  7 ( b ) are shown in Table 1 below: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Typical Hybrid Screen Dimensions 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
               
               
                   
               
               
                 27″ 
                 24″ 
                 31″ 
                 55 ¾″ 
                 72″ 
                 30″ 
                 6″ 
               
               
                   
               
            
           
         
       
     
     The video projector  32  can be positioned at any suitable distance from the screen  20  to illuminate the full interior surface, or various subareas of the full surface, and is preferably wall mounted as shown in FIGS. 1 and 2. A preferred distance from the video projector to the above mentioned hybrid screen is about nine feet, such that, if desired, the projection system is suitable for viewing in a relatively small room. The projection system, however, can be expanded for viewing in larger rooms. A commercially available computer workstation compatible projector  32  having high brightness and resolution that is suitable for use with the present invention is a model called Impression 1280, from a company called ASK, in Fredrikstad, Norway. 
     A suitable computer having a texture mapping graphic system with fast image generation, which can be programmed for carrying out the method of this invention, is a model called Octane available from Silicon Graphics Inc., Mountain View, Calif. 
     Referring specifically now to FIG. 2, an arrangement of the major components of the invention are illustrated. In FIG. 2, the computer system  34 , which includes two workstation monitors  36 , a keyboard  40 , a mouse  42 , and the computer  44 , is positioned on a desktop  48 . The hybrid screen  20  is also positioned on a desktop. As previously mentioned, the video projector  32  is preferably wall mounted a convenient distance from the hybrid screen  20 , and is connected to the computer system  34  via cable  52 . A user of the projection system is illustrated at  50 . 
     FIG. 3 is a perspective view of the hybrid screen  20 , and additionally illustrates a stereo emitter  54 , four audio speakers  56 , and an electromagnetic transmitter  58 , all of which can be used with the present invention. Also illustrated is the position of horizontal support members  60  and  63  for the semidome section. Use of the stereo emitter, which is connected directly to the computer  44 , is an option for viewing with the projection system, and requires battery powered glasses to detect an infrared signal from the emitter  54 . A suitable emitter is a model ESGI, available from a company called StereoGraphics, San Rafael, Calif. 
     Additional information can be supplied to the seismic interpreter with four audio speakers. For example, as specific seismic attribute values change in the data volume, the pitch or amplitude of the audio tones can change accordingly. Using stereo or quad audio will also allow locating the sound source corresponding to the appropriate data area. Still further, multiple attributes may be compared by using different audio frequencies for different attributes, and this could create easily recognizable audio interference responses. 
     Referring now to FIG. 4, there is illustrated a schematic view of the auxiliary paddle screen  59 , which as previously mentioned can be interactively positioned to probe the space within the hybrid screen. The viewing surface of the paddle  61  is approximately one-foot square and can include other shapes like a circle or oval attached to a handle  62 . A tracking device, such as electromagnetic receiver  64 , is mounted on the back side of the paddle screen. The receiver  64  cooperates with the transmitter  58 , which is mounted on the hybrid screen as shown in FIG. 3 to detect the position and orientation of the paddle screen  59  within the viewing volume of the hybrid screen  20 . The electromagnetic receiver  64  is connected to the computer via cable  53  either by direct connection or by interface through a system electronics unit. If a system electronics unit is utilized, it will generally contain the hardware and software necessary to receive information from the transmitter and receiver, compute position and orientation and interface with the computer. Suitable location detectors for tracking the position of the paddle screen, such as the electromagnetic transmitter  58  and receiver  64 , are commercially available from a company called Polhemus, located in Colchester, Vt. Location detectors are disclosed in U.S. Pat. Nos. 3,982,474; 5,453,686; and 5,307,072. 
     Instead of the electromagnetic transmitter and receiver described above, other suitable tracking systems may be used to determine the position and/or orientation of the paddle screen. Other suitable systems include acoustical detection methods, optical detection methods, flexible ribbon tracking systems that utilize fiber optic sensors such as 3-D Shape Tape™ tracker by Measurand Inc.; DC magnetic field tracking devices such as mini Bird tracker by Ascension Technology Corporation; and SpacePad® tracker by Ascension Technology Corporation. 
     Referring now to FIG.  5 ( a ), there is illustrated a schematic view of an auxiliary paddle screen  59  which has a mouse  57  incorporated into handle  62 . By depressing buttons  55  it is possible to pick or select at least a portion of the image displayed on the viewing surface of the paddle  61 . Accordingly, in 3D seismic images it is possible to select faults, horizons or any geometric outline in 3D space by moving the paddle and then depressing a button  55  when the object of interest appears on the viewing surface of paddle  61 . 
     FIG.  5 ( b ) represents an alternative embodiment where a trigger  51  is incorporated onto handle  62 . Images are selected by squeezing trigger  51  when the object of interest appears on the viewing surface  61 . 
     Referring now to FIG. 6, a perspective view of the hybrid screen with the auxiliary paddle screen  59  in use is shown. The viewing surface  61  is in the plane defined by dashed line  111  and displays an image corresponding to the 3D seismic data for its location within the plane defined by dashed line  111 . If desired, the image appearing on the viewing surface  61  can be displayed with cross hairs  113 . The cross hairs are especially useful when utilizing an auxiliary paddle screen  59  in accordance with the embodiments illustrated in FIGS.  5 ( a ) and  5 ( b ). In such embodiments the intersection of the cross hairs indicates the point of selection for the image. 
     FIGS.  7 ( a ) and  7 ( b ) illustrate the shape of horizontal structural members  60  and  63  of the hybrid screen  20 , which are positioned as shown in FIG. 3, and further shows the location of vertically mounted rib type structure members  65 , which in turn support triangular shaped dome panels, not illustrated, that form the semidome concave viewing surface. While structural support members  60  and  63  are useful to provide structural support, it is presently preferred to mold a one piece plastic hybrid screen which does not utilize structural support members  60  and  63 . 
     A 3D graphical hardware and software system for fast image generation will now be described in more detail beginning with reference to FIG. 8, where there is illustrated a simplified computer flow diagram showing the major steps in the method for displaying spatially correct seismic data onto a hybrid screen or a paddle screen according to this invention. The first step  66  is to store in computer memory a set of seismic data in the form of digitized seismic signal traces, which are to be visualized and/or interpreted, to provide the 3D seismic data volume. The next step  68  is to select a desired flat or concave shape for the seismic display of subsurface structure. Using the hybrid screen with appropriate extraction and projection operations, the display could correctly display data on a flat wall, a wraparound, or various combinations of flat walls, with or without a floor or a dome shaped ceiling. Selecting the combination of a semidome ceiling, a cylindrical lower section, and floor will illuminate the entire concave display surface of the hybrid screen. The program then proceeds to create a mathematical model corresponding to the shape of the selected display surface, and inserts the model into computer memory so as to at least partially intersect the 3D seismic data volume as illustrated at step  70 . In step  72  the seismic data intersecting the mathematical model is extracted and mapped onto the surface of a two dimensional image plane. Next, in step  74  video images of the seismic data mapped onto the image plane in step  72  are transferred to a video display buffer using well known texture mapping techniques. Finally, in step  76  the image formed in the video display buffer is projected onto the selected 3D display surface. 
     Referring now to FIG. 9, there is illustrated a computer flow diagram showing more details of the step  70  in FIG. 8 for creating a mathematical model of the selected 3D display surface. As a first step  80  in FIG. 9, the computer program is provided with physical data relating to the desired dimensions of the surface to be modeled, and a selected reference point within the modeled space. The program then proceeds to step  82  for creating the mathematical model of the physical configuration. This mathematical model is one or more algebraic equations describing the locus of all points on the surface to be modeled, and usually involves combinations of known solid 3D shapes such as a plane, a cylinder, a sphere etc. If more than one solid shape is required to describe this surface, multiple equations are used, which in combination can describe a full 3D concave display surface. For example, the previously mentioned hybrid screen can be modeled using the combination of equations describing a sphere, a cylinder and a plane. In step  84 , additional data is provided to the computer program for scaling the model with reference to the data volume, including at least a specified size and target point for the model. In step  86  the mathematical model is scaled to a desired size. Next in step  88  the intersections between the mathematical model and the data volume are determined and, in step  90 , the coordinates of the intersections can be adjusted for a specified orientation and location. Finally, in step  92 , an extracted data set is obtained for mapping data onto the image plane. 
     Referring now to FIG. 10, there is illustrated a computer flow diagram showing more details of steps  72  and  74  of FIG. 8 relating to mapping the extracted data and then displaying the mapped data. In step  100  the computer program is provided with data relating to screen/projector geometry including focal distances, desired ray projection volume, and dimensions of the display surface. Proceeding to step  102 , a mathematical model of an image plane is defined and the extracted data is mapped onto the image plane in step  104  thus producing a mapped data set. From the image plane the mapped seismic data set is projected onto a concave 3D display screen, via a video image buffer, preferably using texture mapping techniques, although other known techniques may be used. 
     Various techniques for texture mapping are well known to those skilled in the field of computer graphics, and these texture mapping techniques are generally used to improve surface details of displayed images. Surface detail attributes commonly texture mapped include color, reflection, transparency, shadows, surface irregularities such as bumps or scratches, etc. In general, the texture mapping process effects mapping of a position on one plane onto a corresponding position of another plane and is suitable for transferring the mapped seismic data from the image plane to the video image buffer, which can then be projected onto the display surface. For further discussion of texture mapping and a survey of applications see, e.g., Haeberli, et al., Silicon Graphics Computer Systems, “Texture Mapping as a Fundamental Drawing Primitive”, Proc. fourth Eurographics Workshop in Rendering, Paris, France, Jun. 1993, pgs. 259-266. 
     Other techniques well known to those skilled in computer graphic arts are also suitable for projecting the computer graphic images, such as direct pixel mapping, which employs a one-to-one correspondence between the computer memory and the useable pixel positions on the screen. 
     Referring now to FIG. 11, there is presented a block diagram illustrating the overall organization of external data input and processing steps for displaying spatially correct seismic data on a concave display device according to this invention. In FIG. 11, the processing steps, which have been previously discussed with reference to FIGS. 8,  9  and  10 , are encircled, the external data inputs are shown as labeled arrows entering a processing step and includes optional data such as well data, fault data, horizon data, attribute data and voice data. The display screen is shown in a square in the lower center of the figure. 
     A further embodiment of the invention will now be described wherein borehole data is displayed in a spatially correct manner. Generally, borehole data comprises data obtained about the sidewall surface of the borehole by acoustic, electrical resistivity, radioactive and/or video imaging technology with little or no penetration into the formation, i.e., 2D borehole image data. Although this embodiment of the invention is described in terms of such sidewall surface imaging or 2D borehole imaging, it should be understood that the techniques disclosed herein are applicable to imaging tools that penetrate deeper into the sidewall. 
     Referring now to FIG. 12, there is illustrated a simplified computer flow diagram showing the major steps in the method for displaying spatially correct two dimensional (2D) borehole data onto a hybrid screen according to this invention. The first step  166  is to store in computer memory a set, or array, of 2D borehole image data, which are to be visualized and/or interpreted. The next step  168  is to select a desired concave shape for the display of subsurface structure. Typically, for borehole imaging, the concave shape chosen will be a semi-cylindrical screen. Using the hybrid screen with appropriate extraction and projection operations, the display would correctly display data on the cylindrical lower section. The program then proceeds to create a mathematical model corresponding to the shape of the selected display surface, and inserts the model into computer memory so as to at least partially intersect the 2D borehole data set as illustrated at step  170 . In step  172  the borehole data intersecting the mathematical model is extracted and mapped onto the surface of a two dimensional image plane. Next, in step  174  video images of the borehole data mapped onto the image plane in step  172  are transferred to a video display buffer using well known texture mapping techniques. Finally, in step  176  the image formed in the video display buffer is projected onto the selected 3D display surface. 
     Referring now to FIG. 13, the computer flow diagram illustrated in FIG. 13 applies to the step  170  in FIG. 12 for creating a mathematical model of the selected 3D display surface. As a first step  180  in FIG. 13, the computer program is provided with physical data relating to the desired dimensions of the surface to be modeled. Also, in step  180 , the computer program is provided with a selected reference point within the modeled space. The program then proceeds to step  182  for creating the mathematical model of the physical configuration. This mathematical model is one or more algebraic equations describing the locus of all points on the surface to be modeled and for borehole modeling will typically be a cylinder or semi-cylinder. In step  184 , additional data is provided to the computer program for scaling the model with reference to the data set, including at least a specified size and target point for the model. In step  186  the mathematical model is scaled to a desired size. Next in step  188  the intersections between the mathematical model and the data set are determined and, in step  190 , the coordinates of the intersections can be adjusted for a specified orientation and location. Finally, in step  192 , an extracted data set is obtained for mapping data onto the image plane. 
     Referring now to FIG. 14, the computer flow diagram illustrated in FIG. 14 applies to steps  172  and  174  of FIG. 12 relating to mapping the extracted data and then displaying the mapped data. In step  200 , the computer program is provided with data relating to screen/projector geometry including focal distances, desired ray projection volume, and dimensions of the display surface. Proceeding to step  202 , a mathematical model of an image plane is defined and the extracted data is mapped onto the image plane in step  104  thus producing a mapped data set. From the image plane the mapped seismic data set is projected onto a concave 3D display screen, via a video image buffer, preferably using texture mapping techniques as outlined in step  206 , although other known techniques may be used. 
     Various techniques for texture mapping are well known to those skilled in the field of computer graphics, and these texture mapping techniques are generally used to improve surface details of displayed images. Surface detail attributes commonly texture mapped include color, reflection, transparency, shadows, surface irregularities such as bumps or scratches, etc. In general, the texture mapping process effects mapping of a position on one plane onto a corresponding position of another plane and is suitable for transferring the mapped seismic data from the image plane to the video image buffer, which can then be projected onto the display surface. For further discussion of texture mapping and a survey of applications see, e.g., Haeberli, et al., Silicon Graphics Computer Systems, “Texture Mapping as a Fundamental Drawing Primitive”, Proc. fourth Eurographics Workshop in Rendering, Paris, France, June, 1993, pgs. 259-266. 
     Other techniques well known to those skilled in computer graphic arts are also suitable for projecting the computer graphic images, such as direct pixel mapping, which employs a one-to-one correspondence between the computer memory and the useable pixel positions on the screen. 
     The application of the invention to borehole imaging provides for a more natural and intuitive means to display borehole data. Additionally, the inventive process allows the viewer to drive up and down the borehole and, hence, easily view data images corresponding to higher and lower positions within the borehole. Also, rotation of the view above the borehole central longitudinal axis is allowed by the invention. Accordingly, the invention allows for animating successive images to effect lifelike movements of the borehole data to effect lateral movement or angular movement within the borehole. 
     In addition, this invention permits interpretation of the borehole data in three dimensions. The 3D representation of the borehole image projected onto the curved screen allows geoscientists to pick layers and features around the perimeter of the borehole, thereby creating an interpretation model that defines the true 3D relationships of the features. Such interpretation model can provide information about size, proportion and orientation of features within a single wellbore and from wellbore to wellbore. 
     It will be recognized that the above described invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the disclosure. Thus, it is to be understood that the invention is not limited by the foregoing illustrative details, but rather is to be defined by the appended claims.