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Claims  |
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I claim:
1. In a video graphics display station, the improvement comprising:
memory means for storing a backdrop viewfile comprising a two dimensional
representation in vector format of a selected view of a complex three
dimensional structure,
toroidal strip writing means for transforming strips of said vector format
representation into pixel bit map data format comprising a sequence of
raster views representing contiguous regions of said selected view, and
panning display means for producing from said raster views a video display
which pans across said selected view,
said toroidal strip writing means including means for detecting when said
display approaches an edge of the region represented by the current raster
view and for thereupon causing transformation of a new strip of said
vector format representation, said new strip representing the contiguous
region of said selected view in the direction of panning but the newly
transformed bit map data being entered into the current raster view to
replace therein a prior strip representing a portion of said selected view
in the direction away from panning travel.
2. A graphics display station according to claim 1 further comprising:
site list storage means for storing a site list describing said complex
structure in a three dimensional coordinate system, and
transformation means for accessing from said site list, and transforming
into said two dimensional vector format for use as said backdrop viewfile,
data corresponding to said selected view of said structure.
3. A graphics display station according to claim 2 wherein said
transformation means also performs hidden surface removal, so that said
backdrop viewfile has hidden surfaces removed.
4. A graphics data handling system for a workstation which operates in
conjunction with a host computer that stores a site list describing in a
three dimensional coordinate system the components of a structure, said
system comprising:
first means for transforming information from said site list into a vector
representation of a specified two dimensional view of a defined portion of
the structure represented by said site list,
file means for storing said vector representation as a "backdrop viewfile",
vector-to-raster transformation means for transforming selectable portions
of said backdrop viewfile vector representation into a pixel bit map
"raster view" representation of at least part of said specified two
dimensional view of said structure,
pixel memory means for storing said raster view representation, and
display means for accessing from said pixel memory means and displaying on
a video screen selectable portions of said raster view.
5. A graphics data handling system according to claim 4 further comprising:
panning means, cooperating with said display means, for causing the
sequential accessing from said pixel memory means of consecutive,
contiguous portions of said raster view, the resultant display on said
video screen comprising an image which appears to pan across the part of
said structure represented by said raster view, and
transformation initiation means, cooperating with said panning means, for
recognizing when the displayed image has almost reached an edge of the
part of said view represented by the current raster view, and for
thereupon causing said transformation means to transform another portion
of said backdrop viewfile representing the portion of said two dimensional
view of said structure adjacent to that represented by the current raster
view in the direction of panning travel into pixel bit map representation,
and to replace this new pixel bit map representation into a portion of the
current raster view containing part of the view of said structure in the
direction away from panning travel.
6. A graphics display station according to claim 4 wherein said
transformation means establishes plural raster views from the same
backdrop file at different scale factors, display of different raster
views thereby facilitating an instant zoom capability.
7. A graphics display station according to claim 4 wherein said first means
establishes plural backdrop files from the same site list, each being from
a different viewpoint, selected video screen displays from raster views
derived from different backdrop files then permitting successive display
of a portion of said structure as seen from successively different
viewpoints.
8. A graphics data handling system which operates in conjunction with a
host computer that stores a site list describing in a three dimensional
world coordinate system the components of a complex three dimensional
structure, said data handling system comprising:
first data handling means for storing two dimensional backdrop viewfile
representation of a certain view of said three dimensional structure, said
storage being in a format in which surfaces are defined as vectors or
polygons with respect to a two dimensional universal coordinate system,
means for accessing data from said backdrop viewfile representation, data
representing a selected area of said certain view being definable and
accessible with reference to said universal coordinate system,
means for transforming data accessed from said backdrop viewfile into a two
dimensional bit map raster view representation of said selected area of
said certain view, each raster view picture element being represented by a
set of data bits associated with a two dimensional raster coordinate
system representing the location along horizontal and vertical axes within
the raster view of the particular picture element,
storage means for storing said data bit sets in a pixel memory and for
establishing a directory listing the relationship between each data bit
set in the raster coordinate system and the corresponding storage location
in said pixel memory, said storage locations being specified in a toroidal
coordinate system, and
video display means for accessing from said pixel memory, by utilizing said
toroidal coordinate system, the bit map data required to present a desired
image of said structure, and for displaying accessed bit map in raster
format on a video screen.
9. A graphics data handling system in accordance with claim 8 further
comprising:
panning control means for requesting that the displayed video screen image
pan across the area of said certain view encompassed by said raster view
representaton, said video display means accessing from said pixel memory
consecutive different sets of pixel bit map data respectively
corresponding to consecutive near adjacent regions of said area, the
resultant displayed video screen image providing a pan effect,
means for detecting when, in the raster coordinate system, the displayed
image has approached an edge of the selected area represented by the
current raster view, and for thereupon causing said means for transforming
to delete from said raster view representation a strip of data in a
direction away from the direction of panning travel, and to initiate
accessing and vector-to-raster transformation of additional data for
replacement into said strip, a corresponding entry being made in said
directory list indicating in the toroidal coordinate system the storage
locations of data bit sets in the replaced strip,
said video display means thereafter accessing bit map data for subsequent
consecutive images from a combination of the unreplaced and replaced
portions of the raster view, by reference to the corresponding pixel
memory addresses in the toroidal coordinate system. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a graphics data handling system for a
computer aided design (CAD) workstation. The system maximizes rapid
accessibility to arbitrarily selectable two dimensional views of a complex
site stored in three dimensional representation by a host computer.
2. Description of the Prior Art
In many computer-aided design applications, a host computer establishes and
stores a three dimensional representation of the item being designed. For
example, in the design of a chemical process plant, the host computer may
assemble a site representation of the plant which consists of a list of
the thousands of pipes, valves, fittings and equipment interconnections
that comprise the plant. The site list may include a geometric description
of each such component, together with the three dimensional coordinates
which spatially locate each component within the plant site.
Advantageously, each engineer working on the plant design will have a
workstation or graphics display system that interfaces with the host
computer and facilitates the display of selected images of the plant being
designed. Such a workstation would permit the engineer to rapidly display
two dimensional views, from arbitrary viewpoints, of arbitarily selectable
portions of the plant represented by the site lists in the host computer.
One objective of the present invention is to provide a graphics data
handling system to facilitate such rapid selectable viewpoint image
display in a CAD workstation.
A particularly useful workstation configuration is disclosed in the
inventor's copending U.S. patent application entitled "Graphics Display
System With Viewports Of Arbitary Location And Content", which was filed
on Nov. 2, 1982 as Ser. No. 438,476. That patent application, which is
assigned to Cadtrak Corporation, the assignee of the present application,
is incorporated herein by reference.
In a workstation incorporating the graphics display system of patent
application No. 438,476 individual viewports or video images of arbitary
arrangement, number, size and content may be produced on the video screen.
Thus e.g., the designer may arbitrarily select which views of the plant
are to be displayed. For example, he could simultaneously display a plan
or elevation view of a major portion of the plant, together with an
enlarged perspective view of the immediate portion of the plant piping
which is undergoing design. He can use a panning capability to move the
displayed viewport image across nearby or distant portions of the plant,
and can zoom in to obtain enlarged views of plant details.
There are certain constraints that limit the display flexibility of such a
system when utilized with a host computer that maintains what may be a
massive site list. For example, if a two dimensional plan or elevation
view of a certain portion of the plant is desired, relatively time
consuming algorithms must be used to convert the three dimensional site
list information into a two dimensional representation that is capable of
being displayed on a video screen. The processing includes culling from
the site list the descriptors of all of the plant components which would
appear in the desired two dimensional view, and converting the geometrical
descriptors of these components and their three dimensional spatial
location information (as contained in the site list) into appropriate two
dimensional vector or raster representations. Additional processing is
required to remove "hidden lines and surfaces" from the resultant two
dimensional transformation (i.e., to remove from the final display the
portions of components which, though present in the plant at the displayed
area, would be hidden from view by other components present in the two
dimensional display). Substantial computer processing time, typically
hours, is required to perform such 3D-to-2D conversion and hidden line
removal. If the designer should then wish to view a different portion of
the plant, even one relatively close to, but not contained within, the
previously transformed region, another time consuming transformation and
hidden line removal computation must be carried out. Minutes or hours may
pass before the new image is available to the designer.
Another object of the present invention is to provide a graphics data
handling system which maximizes the amount of two dimensional graphics
data available to the designer, without requiring additional time
consuming 3D-to-2D transformations to be performed. To this end, another
objective is to provide a system in which backdrop viewfiles are
established in advance, which comprise two dimensional vector
representations of substantial subportions of the site represented in the
host computer. The video images are derived from these backdrop viewfiles,
which are maintained at the workstation. The designer can rapidly access
the design information from these backdrop viewfiles for display with
panning and zoom. By precomputing backdrop viewfiles for each of the plant
subsystems on which the designer is working, the designer will have
instantly available to him views of all of the local and surrounding areas
of the plant which he is likely to use during a design session. There is
no computation delay involved with panning within this region.
A further object of the present invention is to provide a graphics data
handling organization that readily facilitates the generation and storage
of backdrop viewfiles and the arbitary selection and display of viewport
images of portions of the data contained within such viewfiles, with
arbitary panning and zoom capability. To this end, it is an object of the
present invention to provide an organization in which graphics data is
handled in a set of different coordinate systems that (a) maximize the
arbitary availability of such data for video display, while (b) minimizing
the requirements of data storage and complex computation of image
transformation.
SUMMARY OF THE INVENTION
These and other objectives are achieved by providing a graphics data
handling system in which desired viewport images are derived from backdrop
viewfiles that store two dimensional graphics data in vector format. These
backdrop viewfiles, maintained in a "universal coordinate system" UCS, are
derived in advance from three dimensional site information stored in the
host computer in a "world coordinate system" WCS.
Using the appropriate input device, the operator can specify regions of the
graphics data that he wishes to display. An appropriate pixel data storage
controller converts the requisite data from the UCS format in the backdrop
viewfiles into a desired raster view in a pixel memory. This view is in a
"raster coordinate system" RCS.
The user can then specify the desired portions of these raster views that
he wishes to display on the video screen. Viewport images are then
generated in a "toroidal coordinate system" TCS from the raster views.
These are displayed on the video screen at arbitary locations selected by
the user and represented in a "window coordinate system" WiCS.
By using a track ball, cursor or like input device, the operator can pan
any viewport image across the data contained not only in the corresponding
raster view, but across the larger graphics image area represented in the
backdrop viewfiles. As soon as a viewport image is panned near an edge of
the corresponding raster view, additional graphics data is transformed
from the backdrop viewfile into the raster memory in "toroidal" strip
writing fashion. Panning can continue across this new graphics data
without interruption. The fact that the graphics data in the raster view
is changing in a toroidal fashion, and the fact that this data is being
accessed toroidally for generation of the viewport image, is not apparent
to the user, who sees only a smoothly panning image.
The operator may also control the zoom magnification of each viewport
image. The inventive graphics data handling system incorporates a
capability that both permits each raster view to be produced with a
selectable magnification factor with respect to the data in the backdrop
viewfile, and which independently permits the viewport image to be
magnified with respect to the raster view from which it is derived.
The usefulness of the invention is best understood when the time taken to
achieve the above transformations is understood. For a process plant with
2500 piping components (valves, tees, elbows, etc.) the production of each
backdrop viewfile from the three dimensional site information takes
approximately one hour using conventional hidden line removal algorithms
on a typical medium size computer. Production of a typical raster
coordinate system view from a backdrop viewfile typically takes one to
five seconds using an implementation of the present invention using a
16-bit microprocessor. With such a workstation, transforming a view from
the raster coordinate system to the video screen takes place in 1/60 of a
second. An arbitrarily large number of raster coordinate system views (of
differing viewpoint or difering scale factor) can be stored simultaneously
in the raster memory, limited only by the size of raster memory provided.
Smooth panning (60 screen updates per second) may take place at up to 3
inches per second.
BRIEF DESCRIPTION OF THE DRAWINGS
A detailed description of the invention will be made with reference to the
accompanying drawings wherein like numerals designate corresponding
elements in the several figures.
FIGS. 1A and 1B comprise a pictorial representation of the various graphics
data formats in a host computer and a CAD workstation utilizing the
inventive graphics data handling system.
FIG. 2 is a block diagram of a CAD workstation utilizing the graphics data
handling system of the present invention.
FIG. 3 is a pictorial view illustrating the toroidal entry of data into a
raster view, and the toroidal readout of data from that raster view to
produce a viewport image, as implemented by the CAD workstation of FIG. 2.
FIG. 4 illustrates the memory assignment of raster view data in the pixel
memory of the CAD workstation of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The following detailed description is of the best presently contemplated
mode of carrying out the invention. This description is not to be taken in
a limiting sense, but is made merely for the purpose of illustrating the
general principles of the invention since the scope of the invention is
best defined by the appended claims.
FIGS. 1A and 1B illustrate the various data formats utilized by a host
computer 10 and a CAD workstation 11 (FIG. 2) employing the inventive
graphics data handling system. It should be understood that the computing
functions of the host computer 10 may well be performed on the workstation
CPU (block 45, FIG. 2) as it would also be a general purpose computer. By
way of example only, these figures depict a CAD application involving the
design of a chemical process plant, however the invention is not so
limited.
As the chemical process plant is developed, the host computer 10
establishes (block 12, FIG. 1A) a "site list" of all of the constituent
elements in the plant. This list is established in conjunction with an
index (block 13) of standard components that is also maintained by the
computer 10. For example, this component list may include the name of a
component (e.g., pipe section, elbow, tee, nipple, valve) together with a
set of geometric descriptors for that component.
The geometric descriptors of a pipe section may comprise a pair of
concentric cylinders representing respectively the inside and outside
surfaces of the pipe section. The component index may indicate that there
are three dimensional descriptors associated with the pipe section,
namely, the inside diameter, the outside diameter (or alternatively, the
wall thickness) and the length. The index may also specify a material
type, manufacturer and other data.
The site list may comprise an ordered table of all of the components
included within the chemical plant, together with the coordinates locating
each such component within the site. Herein, this is called the "world
coordinate system" WCS, and is used to specify each component location in
three dimensional space.
The inset view 14 of FIG. 1A is a pictorial representation of part of a
chemical process plant that might be represented by the site list in the
computer 10. (No such visual image is present in the host computer, and
the view 14 is provided only to aid in explanation of the present
invention.) For each component of the plant there will be a corresponding
entry in the site list. For example, for the pipe section 15, the list
entry might specify "pipe section" (with reference being made to the index
of standard components to obtain the geometric descriptors thereof), of
length 10 feet, inside diameter 1 inch and outside diameter 1.5 inches.
The site list will specify the location of the pipe section 15 with
respect to the X, Y and Z coordinates of the WCS. For example, the center
of the pipe section 15 may be situated at a position x=25 feet, y=30 feet,
3 inches and z=12 feet, 2 inches with the pipe axis parallel to the WCS
x-axis. The site list may also indicate that one end of the pipe section
15 is connected to a tee (the tee 17 in view 14) and that the other end is
connected to an elbow 18.
Different organizations may be used for the site list. For example, instead
of listing each plant component separately, these may be arranged in
groups. Thus the site list may specify as a single "pipe" a set of
components that are directly interconnected. For example, in the view 14,
a "pipe" 19 may be defined as having several pipe sections 15, 20, 21, 22
connected in a certain order with a tee 17 and an elbow 18. Such an
ordering of "pipe" and "components" may simplify the handling of data in
the site list.
Regardless of particular arrangement, however, the site list is
characterized with respect to the present system as specifying the three
dimensional location of each plant component in terms of the world
coordinate system, i.e., a coordinate system that established the relative
position of each plant component with respect to each other in the actual
plant as it will finally be constructed (or in a scaled version thereof).
At the other end of the computer aided design system is a video display
screen 25 which is part of the workstation 11. On the screen the designer
wishes to display certain "viewport images" V.sub.1, V.sub.2 (FIG. 1B)
that are two dimensional views of portions of the plant being designed.
The workstation 11 utilizes the inventive graphics data handling system to
optimize the conversion of data contained in the site list into a format
for display on the screen 25 with maximum accessibility and selectability.
To this end, the workstation 11 generally employs a raster scan display
technique set forth in the inventor's U.S. Pat. No. 4,197,590 entitled
"Method For Dynamically Viewing Image Elements Stored In A Random Access
Memory Array" and U.S. Pat. No. Re. 31,200 entitled "Raster Scan Display
Apparatus For Dynamically Viewing Image Elements Stored In A Random Access
Memory Array".
In this regard, the workstation 11 includes a control pixel memory 26 which
stores raster views of selected portions of the plant represented by the
site list in the computer 10. In each raster view, the graphic image is
stored in the form of picture element ("pixels") each of which may
represent a single dot on a video screen display (at 1:1 magnification) of
that raster view.
Each pixel is represented by a set of bits in the pixel memory. If a only a
black and white display is required, each pixel may be represented by a
single bit, which may be "1" for black and "0" for white. Alternatively,
each pixel may be represented by set of plural bits which may define a
gray scale, a color, or an address to a color map which in turn defines
the color of the corresponding picture element.
The sets of pixel bits which make up a complete raster view may be stored
at contiguous or non-contiguous locations in the pixel memory. For
example, the sets of bits representing the pixels in a complete horizonal
line of the raster view may be stored in contiguous locations of the pixel
memory. Similar sets of pixel data for consecutive lines in the raster
view likewise may be stored in consecutive groups of locations of the
pixel memory.
In accordance with the teachings of the above-identified U.S. Pat. Nos.
4,197,590 and Re. 31,200 the data in the pixel memory is accessed in real
time, in synchronism with the horizontal and vertical scanning of the
video display screen 25, and used to control the color and intensity
modulation of the CRT. In this manner, the pixel data is converted to an
actual image on the video screen 25.
Each raster view is a representation of a two dimensional view of a portion
of the plant represented by the site list in the host computer 10. Five
such raster views 27 through 31 are shown in FIG. 1B. Although illustrated
pictorially in FIG. 1B, in fact each such raster view consists of a set of
digital data stored in the pixel memory 26 and representing (in the manner
just described) the individual picture elements which comprise the
respective views. Within each such raster view, each pixel may be
identified by a corresponding position in the two dimensional "raster
coordinate system" RCS. For example, the pixel 27a at the lower left
corner of the raster view 27 has the coordinates x=1, y=1 in the RCS
wherein the x-axis is measured by pixel positions across each horizonal
line, and the y-axis is measured by lines going from the bottom to the top
of the raster view.
By way of example, the pixel 27b in the raster view 27 is located at x=370,
y=20 in the RCS. This pixel is actually represented by a set of one or
more bits which define an intensity or color of the corresponding pixel,
and which are stored at certain memory locations in the pixel memory 26
that correspond to the RCS location (370, 20). The actual mapping or table
which lists the correspondence between each pixel position in a raster
view and the corresponding actual memory address or addresses in the pixel
memory 26 is established and maintained by a controller 32 which is part
of a graphics control unit 33 in the workstation 11.
Under operator control, any of the raster views stored in the pixel memory
26 may be displayed at arbitary positions and magnifications on the video
screen 25 within 1/60th of a second. In the example of FIG. 1B, the raster
view 31 is displayed at 1:1 magnification as the viewport image V.sub.2,
while a portion 30a of the raster view 30 is displayed in magnified form
as the viewport image V.sub.1. Such seective readout and display of the
stored raster views advantageously is accomplished by the workstation 11
in accordance with the teachings of the inventor's above-identified
co-pending patent application, Ser. No. 438,476 entitled "Graphics Display
System With Viewports Of Arbitary Location". The display control section
34 of the workstation 11 cooperates with a viewport image requester 35 and
a control table assembler 36 to read out and display the desired
information from the pixel memory 26.
The desired location and size of each viewport image on the video screen 25
is specified in a "window coordinate system" WiCS that is defined in terms
of pixel locations on the actual video screen. Thus the WiCS is a two
dimensional coordinate system in which the x-axis is measured in terms of
pixel locations across a line of the CRT screen, and in which the y-axis
is measured in terms of lines on the video screen going from bottom to
top. By way of example, the origin (bottom left corner of the viewport
V.sub.1 in FIG. 1B is located at coordinates (400, 25) in the WiCS while
the upper right corner is located at coordinates (668, 325).
While the selection and display of the various raster views may be
accomplished readily and quickly, establishing the raster views from the
data contained in the site list of the host computer would be very time
consuming if done directly. Thus if the designer needs to display a
portion of the plant which is not contained within a present raster view,
even though the desired plant elements may be contiguous to those shown in
the present raster views, a great deal of computation time would be
required to generate the new raster view directly from the site list. This
clearly is an undesirable condition.
To alleviate this problem, the graphics data handling system of the present
invention utilizes an intermediate set of "backdrop viewfiles" 40 through
42 (FIG. 1A) which advantageously are resident in disc storage 43 in the
workstation 11.
Each backdrop viewfile comprises a vector representation of a selected two
dimensional view of a portion of the plant that is being designed.
Typically, the represented portion of the plant is in the area that the
designer is currently working, and is larger in extent that the region
which would be selected by the designer for display as a viewport image.
As discussed in more detail below, the raster views 27 through 31 are
derived from these backdrop viewfiles 40-42.
The desired backdrop viewfiles are specified (block 44, FIG. 1A) to the
host computer 10 by a central processing unit (CPU) 45 in the workstation
11 in response to a user input designating the region of the plant which
he desires to display. For example, the user may utilize a keyboard or
other input peripheral 46 to specify that he will need plan, elevation and
isometric views of a particular region of the plant being designed.
From this information, the CPU 45 will establish a view definition matrix
or assemblage of data which specifies to the host computer the type of
backdrop viewfiles which are required, and the region of the plant which
is to be encompassed therein.
As an example, the user may specify that he is interested in the region of
the plant bounded by certain coordinates in the WCS. For example, he may
be interested in viewing components of the plant which are physically
situated in the cube that is bound by the origin (0, 0, 0) of the WCS at
the left bottom front corner and the coordinates x=25 feet, y=25 feet,
z=25 feet at the upper right rear corner.
The user will also specify the desired views. For example, these may
include a plan view through a certain defined horizontal plane in the
world coordinate system (e.g., a top view through the plane x=25 feet), an
elevation view through a defined vertical plane, and an isometric view
from a defined viewpoint. Such view planes and isometric viewpoints are
specified in the world coordinate system.
From this view definition matrix information, the host computer generates
(block 47, FIG. 1A) the desired backdrop viewfiles from the information
contained in the site list. Each such viewfile consists of an ordered list
of vectors which define a two dimensional image of the specified portion
of the plant as viewed in the manner defined for the particular viewfile.
For example, the backdrop viewfile 40 illustrated in FIG. 1A represents a
top plan view of the designated portion of the plant (i.e., as viewed from
the top at the plane Y=25 feet). The illustrated backdrop viewfiles 41 and
42 represent elevation and isometric views of the same portion of the
plant, respectively along the plane and from the viewpoint specified in
the view definition matrix.
The number of backdrop viewfiles is arbitary, as is the selection of views
therein. Thus more or less than three viewfiles may be utilized by the
workstation 11. Furthermore, although the three viewfiles 40-42
illustrated in FIG. 1A are of the same region of the plant, this is not
necessary. Indeed, more often backdrop viewfiles of different regions of
the plant may be preestablished and maintained in the disc storage 43.
Although each of the backdrop viewfiles 40-42 is illustrated pictorially in
FIG. 1A, in actuality the viewfiles are not themselves in pictorial
format. Rather, they are in the form of digital data representing vectors
that in turn represent image lines in the selected plan, elevation or
isometric view. The vectors are defined in a two dimensional "universal
coordinate system" UCS. For each such backdrop viewfile, this coordinate
system may have its origin e.g., at the lower left corner of the two
dimensional image represented by the vectors comprising an individual
backdrop viewfile.
For example, the backdrop viewfile 40 may comprise a list of vectors
specified with respect to a UCS origin at the lower left corner of the
represented top plan view. In the backdrop viewfile 40, the pipe section
15 may be defined by four vectors representing straight lines connecting
the points having designated UCS coordinates (x.sub.1, y.sub.1), (x.sub.2,
y.sub.1), (x.sub.2, y.sub.2) and (x.sub.1, y.sub.2). The definition of the
backdrop viewfile 40 as a list of vectors is convenient for illustration.
In fact other forms, such as filled polygon patches for showing shaded
raster images, may be used instead. The important point is that the
backdrop file has a form that can be transformed into pixels in the raster
coordinate system at high speed.
The vector listing which comprises each backdrop viewfile in the UCS is
generated by the host computer. This computation may take a very long
time, typically many minutes or even many hours, depending on the
complexity of the plant region that is represented by the desired backdrop
viewfile. As part of the viewfile generation, the host computer
advantageously will remove hidden lines from each view. Thus in the
elevation and isometric backdrop viewfiles 41 and 42, the portions of the
pipe branch 48 which lie behind the tanks 49 and 50 are hidden from view.
In these viewfiles the pipe branch 48 respectively may be represented by
three separate sets of vectors that define only the portions of the pipe
branch 48 which would be seen in a corresponding elevation or isometric
image.
The 3D-to-2D transformation algorithms with hidden line removal utilized by
the host computer 10 may be conventional. The computation of such
transformation typically is very time consuming. What is not conventional
in the present invention is the use of backdrop viewfiles (in a two
dimensional, vector format) as an intermediate step to the generation of
the raster views from which the video displays are generated. This is a
significant feature of the present invention, in that the production of
such raster views can be accomplished very quickly (typically in seconds)
so that the selection of new views for display on the video screen does
not necessitate long delays (as was required in the prior art) while the
host computer generated the requisite raster views directly from the site
list or other primary data. In the case of toroidal panning, continuous
smooth pan can be readily accomplished as described in patent application
Ser. No. 438,476.
Generation of the raster views is carried out by a backdrop-to-raster
conversion and pixel data storage controller 32 which is part of the
graphics control unit 33 in the workstation 11. Initially, the operator
can select (using keyboard or graphical input) a set of raster views to be
generated and stored in the pixel memory 26. Generally, each raster view
is derived from a corresponding one of the backdrop viewfiles, and
comprises a raster or pixel representation thereof. For example, the
raster view 31 (FIG. 1B) is a pixel representation of the entire elevation
view that is represented in vector format by the backdrop viewfile 41. The
designation RCS2-1 indicates that this is the first raster view generated
from the elevation UCS2 of FIG. 1A. This raster view RCS2-1 is, for
example, approximately 320 pixels across as contrasted with the backdrop
viewfile UCS2 which may be 64,000 dimensional units (in UCS) across,
meaning that the transformation from vector to raster format (and from UCS
to RCS coordinate systems) has been made with, magnification or scale
factor of 1/200. The raster view 31 contains all of the pictorial
information contained in the backdrop viewfile 41.
The raster view 30 of FIG. 1B is derived from the isometric backdrop
viewfile 42. In this raster view, only a portion of the image represented
by the backdrop viewfile 42 has been converted to pixel format, with a
scale or magnification factor Sfac of approximately 1/125 (i.e.,
Sfac=1/125). The raster views 27-29 each have been derived from the
backdrop viewfile 40, with different scale factors.
Transformation from the vector format of the backdrop viewfile to the pixel
format of the raster views is relatively straightforward. For example, it
may simply comprise accessing each linedefining set of vectors from the
backdrop viewfile, and writing in a "1" to each pixel memory position
corresponding to the loci of the line defined by that set of vectors.
Since the universal coordinate system UCS and the raster coordinate system
RCS are two dimensional, the transformation requires in general one
addition (offset) and one multiplication (scaling) per axis, and can be
performed very quickly by the CPU 45. Since hidden lines already have been
removed in the backdrop viewfiles, no complex algorithms must be carried
out by the CPU 45 to eliminate hidden lines from the raster views. This
time consuming work already has been done in advance in association with
the 3D-to-2D transformation carried out by the host computer when the
backdrop viewfile was created.
As described hereinabove, the actual viewport images which are displayed on
the video screen 25 are obtained by raster readout of all or selected
portions of the raster views stored in the pixel memory 26. The manner in
which this is accomplished by the display control section 34 in
cooperation with the graphics control unit 33 is set forth in the
inventor's above-identified copending U.S. patent application Ser. No.
438,476. Generally, the operator first defines the size and location of
the desired viewports V.sub.1, V.sub.2 in the window coordinate system.
The operator next specifies what images are to be displayed in each of
these viewports. Such images may be defined by indicating: (a) the
specific raster view that is to be reproduced, (b) the viewport in which
the view is to appear, (c) the magnification or pixel replication zoom
scale factor to be used, and (d) if less than the entire raster view is to
reproduced, the location within the raster view of the bottom left corner
of the portion of the view that is to be displayed.
From the foregoing information, the control table assembler 36 in the
graphics control unit 33 assembles a list of control words, the details of
which are specified in the above-identified copending application, Ser.
No. 438,476. In general, the control table includes a set of control word
sequences that specify the locations within the pixel memory 26 that
contains the raster view pixel data which is to be accessed sequentially
to provide the video modulation information for each scanned row of the
video screen CRT. The display control section 34 utilizes portions of the
control word information and accessed pixel data to produce the
appropriate drive signal for the video screen. For example, when scanning
the video line 55 (FIG. 1B), viewport information earlier provided to the
display control section 34 in the window coordinate system defines the
left and right end locations 55a, 55b of the viewport V.sub.2, and
specifies that the remainder of the video scan line 55 should be of the
interviewport color, since it intersects no other viewport. The display
control section 34 uses this information to gate pixel data to the video
screen during the time that the CRT beam is traversing the scan line
region between the viewport left edge 55a and right edge 55b.
In the illustration of FIG. 1B, the image in the viewport V.sub.2 is a
1-to-1 reproduction of the raster view 31 which itself is a 1:200
representation of the backdrop viewfile 41. Upon operator specification
(e.g., via a keyboard or other peripheral 46) to the graphics control unit
33 of the desired viewport | | |
