JP4133727B2 - Graphic data conversion method and program, and data structure - Google Patents

Description

  The present invention relates to a CAD (Computer Aided Design) data conversion technique.

There are a wire frame model, a surface model, a solid model, and the like as models for expressing a solid in the CAD system, but the solid model is currently mainstream. In this solid modeling, for example, a complicated tolerance system is defined inside as described in Japanese Patent No. 3087497, and even if data in a specific solid modeler is converted to another solid modeler, it remains as it is. In many cases, processing cannot be continued. This cause will be described in a simplified manner with reference to FIG. Ideally, the surface segment 1000, the surface segment 1003, and the ridgeline 1001 representing the boundary (intersection line) between the surface segment 1000 and the surface segment 1003 should be connected, but the surface segments 1000 and 1003 and the ridgeline Due to the expression format 1001, etc., in practice, there is often a divergence between them as shown in FIG. However, if the magnitudes ε ₁ and ε ₂ are within a predetermined tolerance range in a specific CAD system A, the specific CAD system A has surface segments 1000 and 1003 and a ridgeline 1001. Are determined to be connected, and various graphic operations can be performed. It is also possible to convert the data of the specific CAD system A into data for another CAD system X. However, tolerances that are defined in the other CAD system X is less than the tolerance at a particular CAD system A, in the other CAD system X is greater than the magnitude epsilon ₁ and epsilon ₂ tolerance deviation As a result, there may occur a case where the surface portions 1000 and 1003 and the ridgeline 1001 are not connected. That is, an error occurs in the graphic operation, and the process cannot be continued. In some cases, conversion of data from a specific CAD system A to the other CAD system X cannot be performed.

On the other hand, there is a technology that subdivides patches or segments that make up surface segments and ridge lines to reduce the above-mentioned divergence, but it cannot deal with all cases, and the amount of data is There is a problem of increasing.
Japanese Patent No. 3087497

  As described above, conventionally, there has been a problem when processing CAD data of a specific CAD system in another CAD system. Also, even in graphic operations within the same CAD system, the divergence may increase in some cases, making it impossible to continue processing.

  Accordingly, an object of the present invention is to provide a technique for enabling CAD data to be appropriately processed in a graphic operation performed later.

  The graphic data conversion processing method according to the first aspect of the present invention is expressed by using a set of Bezier composite curved surfaces (control points that are connection points (hereinafter referred to as connection control points) and internal control points that are not connection points. Trimming patches, such as curved surfaces such as Bézier compound surfaces and rational Bézier compound curves, with Bézier compound curves (for example, ridge lines obtained by curves such as Bézier compound curves and rational Bezier compound curves) composed of specific segments Identifying a base patch that is not trimmed by the Bezier composite curve among the surface segments obtained by storing the base patch data in the graphic data storage unit, and of the Bezier composite curved surface Of the patch trimmed by the Bezier compound curve, the part included in the above-mentioned surface segment is used with a constant parameter line determined from the base patch. A division step for dividing the patch into a quadrangular patch and a triangular patch according to a predetermined rule, and a vertex that is a boundary of the face segment among the vertices of the quadrangular patch and the triangular patch is set to a corresponding point on the Bezier composite curve. Moving the side that is the boundary of the face portion to the corresponding part of the Bezier compound curve, and storing the data of the quadrilateral patch and the triangular patch after the movement processing in the graphic data storage unit. Including.

In this way, the portion included in the above-mentioned surface portion of the patch to be trimmed by the ridge line which is a Bezier composite curve among the Bezier composite curved surface is divided into a quadrangular patch and a triangular patch, and the vertex of the quadrilateral and the triangular patch and At least C ⁰ continuity can be guaranteed by moving the sides of the triangular patch onto the above-mentioned Bezier system composite curve. Therefore, it is possible to avoid a situation in which data exchange is not successful due to the presence or absence of tolerance between different CAD systems. It should be noted that subdividing patches in this way can be carried out mathematically and accurately in the case of a tensor product type compound curved surface such as a Bezier type compound curved surface, and the present invention utilizes this property. Yes. In addition, since it is suitable for controlling the position of the connection point, a Bezier composite curved surface and a Bezier composite curve are used.

  Further, in the dividing step, the dividing may be performed by further using a constant parameter line obtained from the parameter values of the points on the surface corresponding to the segment connection points of the Bezier composite curve. In this way, by performing division using the parameter constant line obtained from the parameter value of the point on the surface corresponding to the segment connection point of the Bezier compound curve, the triangle patch or quadrilateral patch generated is generated. It is possible to avoid another divergence from occurring when the moving step is performed on the vertex or side and the ridgeline.

  Further, the moving step includes a step of further dividing the Bezier composite curve at a point on the Bezier composite curve corresponding to the vertex that is the boundary of the face portion among the vertices of the quadrilateral patch and the triangle patch. Also good. In this way, a specific segment of the ridge line corresponds to the hypotenuse (side that becomes the boundary of the surface segment) of the triangular patch, and subsequent management and processing becomes easy. Since the Bezier type composite curve is also a tensor product type composite curve, even if it is divided at any point, it can be mathematically accurately divided and no problem occurs.

  The data structure according to the second aspect of the present invention is a data structure representing a surface segment obtained by trimming a Bezier compound curved surface by a Bezier compound curve (ridge line) constituted by a specific segment, A data structure for a base patch group that is not trimmed by the Bezier composite curve among the surface segments, including data for specifying each base patch, and a data structure for managing the base patch group And the four sides obtained by dividing the portion included in the surface portion of the patch trimmed by the above-mentioned Bezier composite curve among the Bezier composite curved surface using a constant parameter line determined from the base patch and according to a predetermined rule A data structure for a shape patch group and a triangle patch group, which is a data structure for specifying each quadrilateral patch and each triangle patch. Include is intended to include a data structure and a data structure for managing a data structure and a triangle patch group to manage the quadrilateral patch group.

  By maintaining such a data structure, it is possible to continue graphic operations in an appropriate form in any CAD system.

  The method of the present invention can create a program for causing a computer to execute the method, and the program and the data structure are stored in, for example, a flexible disk, a CD-ROM, a magneto-optical disk, a semiconductor memory, a hard disk or the like. Stored in a medium or storage device. Moreover, it may be distributed as a digital signal via a network or the like. The intermediate processing result is temporarily stored in a storage device such as a memory.

  According to the present invention, CAD data can be appropriately processed in a graphic operation performed later.

  FIG. 2 shows a functional block diagram according to an embodiment of the present invention. The CAD-A system 1 is a specific CAD system that has existed in the past, and geometric data of a figure generated in the CAD-A system 1 is stored in the CAD-A data storage unit 3. In order to convert the data stored in the CAD-A data storage unit 3 so that graphic operations can be performed without any problem in other CAD systems, the format conversion unit 5 and B-spline CAD data storage The unit 7, the base graphic conversion unit 9, the Bezier CAD data storage unit 11, the hybrid patch conversion unit 13, the hybrid patch storage unit 15, and the base patch conversion unit 17 are used.

  The format conversion unit 5 performs geometric format conversion, phase format conversion, attribute format conversion, and the like. In the conversion of the geometric format, although it may be an approximation in some cases, the representation format (Canon) of the base figure of the curve and the curved surface is converted. Here, the geometric data for the CAD-A system 1 is converted into a B-spline system or a Bezier system. When the geometric data for the CAD-A system 1 is already expressed in a B-spline system or a Bezier system, conversion of the geometric format is unnecessary. The B-spline system includes B-splines and NURBS (Non Uniform Rational B-Spline), and is a convenient expression format for controlling continuity between patches and segments. In addition, Bezier systems include Beziers and rational Beziers, and curves and curved surfaces pass through connection control points, which is a convenient expression format for position control of connection points of patches and segments. In the phase format conversion, the expression format of vertices, ridges, and faces is converted. For example, although there are expression forms such as winged edge, half edge, and radial edge, they are not the main points of the present embodiment, and may be converted into any expression form. If the same format as the conversion destination is also used in the CAD-A system 1 for the conversion of the phase format, it is not necessary to carry out the conversion. In the attribute format conversion, the system-specific attribute value is converted. However, this is not the gist of the present embodiment, so that it is converted into a predetermined expression format determined in advance. The attribute value is not necessarily data that can be completely converted. When the format conversion unit 5 converts the data into the B-spline system in the geometric format conversion, the converted data is stored in the B-spline system CAD data storage unit 7. On the other hand, when converted to the Bezier system, the converted data is stored in the Bezier CAD data storage unit 11.

  The base graphic conversion unit 9 performs processing for converting the B-spline geometric data stored in the B-spline CAD data storage unit 7 into Bezier geometric data, and converts the converted data into Bezier CAD data. Store in the storage unit 11. The process of converting B-spline geometric data into Bezier geometric data is well known and will not be described in detail here. Note that the transformation of the base figure can be performed accurately, not approximation. As described above, when the Bezier geometric data is generated from the beginning by the format conversion unit 5, it is not necessary to perform the processing by the base graphic conversion unit 9.

  The hybrid patch conversion unit 13 generates hybrid patch data including triangular patches and quadrilateral patches by performing processing described in detail below, and stores the hybrid patch data in the hybrid patch storage unit 15.

  The graphic operation unit 19 performs graphic operations such as cut-out of faces, boolean (set operation), and fillet on the data stored in the hybrid patch storage unit 15. Inside these graphic operations, the surface is cut and a new surface is generated. At this time, the divergence between the base curved surface and the curve of the ridge line has been a problem in the past. By generating the hybrid patch according to the form, a problem does not occur in such graphic operations. Therefore, the types of graphic operations are not limited to these, and other graphic operations are also performed.

  The base patch conversion unit 17 generates Bezier geometric data from the data stored in the hybrid patch storage unit 15 and the data stored in the Bezier CAD data storage unit 11, and stores the Bezier CAD data. Stored in the unit 11. That is, the base curved surface before performing the graphic calculation may be used as it is, or may be cut out and used as necessary. In the case of fillets, a curved surface expressed by a quadrilateral patch is generated, and can be stored as it is.

  Further, the format conversion unit 5 and the base graphic conversion unit 9 also perform conversion in the direction opposite to the conversion direction described above. That is, by combining with the base patch conversion unit 17, the data stored in the hybrid patch storage unit 15 and processed by the graphic calculation unit 19 can be appropriately used in the CAD-A system 1. However, since it is not always necessary to return the data to the CAD-A system 1 again, the processing of the flow of the base patch conversion unit 17, the base graphic conversion unit 9, and the format conversion unit 5 may not be performed.

  Next, processing contents of the hybrid patch conversion unit 13 will be described with reference to FIGS. First, the data stored in the Bezier CAD data storage unit 11 is read. For example, as shown in FIG. 4, a case is considered in which a segment 150 is formed by trimming a Bezier composite curved surface 200 (basic curved surface) using segments 101 to 103 that form ridge lines that are Bezier composite curves. . The Bezier composite curved surface and the Bezier composite curve are a tensor product type composite curved surface and a composite curve. The “composite” of this composite curved surface indicates that a plurality of patches are connected. “Tensor product” represents a multiple linear space. That is, the Bezier-type composite curved surface 200 is composed of quadrilateral patches A to K in the portion shown in FIG. Each of the patches A to K is defined by a connection control point and an internal control point that are connected to other patches. Dotted lines 110 to 114 represent parameter constant lines in which the U value of the parameter represented by (U, V) is constant in the parameter space for the Bezier composite curved surface 200, and dotted lines 115 to 118 represent the V values. Represents a constant parameter line where is constant. Connection control points exist on the dotted lines 110 to 118. As can be seen from the patches A to K, the patches are regularly arranged, and in the parameter space (U, V), the parameter values U and V increase monotonously in the direction shown in FIG. .

  The segment 101 and the segment 102 have end points near the vertex 104, but are not connected here. In addition, the segment 102 and the segment 103 are connected at a segment connection point 105. The ridgeline defines a loop direction from right to left in FIG. It is assumed that the segments 101 to 103 and the vertex 104 do not exist on the Bezier composite curved surface 200 and a divergence occurs.

Returning to the description of FIG. 3, the hybrid patch conversion unit 13 is based on data read from the Bezier CAD data storage unit 11 and is a base that is a patch that is not trimmed by the segments 101 to 103 constituting the ridgeline. The patch is specified, and the data of the base patch is stored in the hybrid patch storage unit 15 (step S1). In the example of FIG. 4, patches (base patches) that are not trimmed into the segments 101 to 103 are the patch I, the patch H, the patch N, the patch H, the patch M, and the patch L. Note that patch E is not included here because it is not included in area 150. Such base patch data is stored in the base patch data storage section in the hybrid patch storage section 15 as shown in FIG. In the example of FIG. 5A, in the (U, V) space for the base curved surface, the column of diagonal connection points 1 that stores the parameter values of the first diagonal connection points of the base patch that is a quadrilateral, A row of diagonal connection points 2, a row of control points 1 storing the coordinate values of the first control point among the 16 control points of the base patch (4 vertical and 4 horizontal),. . . And a column of control points 16 for storing the coordinate values of the 16th control point among the 16 control points of the base patch. The order of registration of the base patches is, for example, arranged in ascending order of the parameter values of the first diagonal connection point. In the example of FIG. 4, the patch N, patch M, patches H, patches L, they are arranged in the order of patch I.

  Next, the hybrid patch conversion unit 13 sets a parameter value (U and V) of the diagonal connection point of each base patch stored in the base patch data storage unit, and a perpendicular line from the segment connection point 105 to the Bezier complex curved surface 200. Parameter values (U and V) of intersections with the perpendiculars when lowered (hereinafter referred to as segment connection points), intersections with the perpendiculars when perpendiculars are drawn from the vertex 104 to the Bezier composite curved surface 200 Parameter values (U and V) (hereinafter referred to as points corresponding to vertices), and parameter values at the intersection with the perpendicular when the perpendicular is drawn from the inflection point of the ridge line to the Bezier composite curved surface 200, if any (U and V) are acquired and temporarily held in the storage device (step S3).

  Then, a parameter constant line is generated for each of the acquired parameter values (step S5), and an intersection line (hereinafter referred to as a ridge line equivalent line) between the parameter constant line and the perpendicular line when the perpendicular line is dropped from the ridge line to the Bezier-based composite curved surface 200. Alternatively, a parameter value (hereinafter referred to as an intersection parameter value) of the intersection with the boundary is calculated and temporarily stored in the storage device (step S7). The parameter constant line generated in step S5 is not further extended when it contacts the boundary of the base patch. Then, a constant parameter line of the intersection parameter value is generated (step S9). The constant parameter line generated in step S9 is not further extended when it contacts the boundary of the base patch. Note that if the intersection of the constant parameter line and the ridge line equivalent line is detected as a result of step S9, steps S7 and S9 are repeated.

  Steps S5 to S9 will be described with reference to FIG. 6, which is the same example as FIG. The constant parameter line generated in step S5 includes dotted lines 110 to 118 related to the boundary of the base patch, a one-dot chain line 121 related to the point corresponding to the vertex of the vertex 104, and a point corresponding to the segment connection point of the segment connection point 105. Dotted lines 122 and 123 related to. The intersections of these parameter constant lines and the ridge line equivalent lines are point 161, point 162, point 165, point 166, point 167, point 168, point 169 and point 170. Furthermore, the parameter constant lines that pass through these points and are generated in step S9 are two-dot chain lines 131, 132, 135, 136, 137, 138, and 139. The intersections of the two-dot chain line and the ridge line equivalent line are points 163 and 164. Parameter constant lines passing through the points 163 and 164 and further generated in step S9 are two-dot chain lines 133 and 134.

  Next, the hybrid patch conversion unit 13 calculates the intersection of the constant parameter line, and temporarily stores the data of the intersection in the storage device (step S11). And the process which subdivides the said ridgeline in the point on the ridgeline corresponding to the intersection of a parameter fixed line and a ridgeline equivalent line is performed (step S13). In the example of FIG. 6, the ridge line is subdivided at points on the ridge line corresponding to the points 161 to 169. Since the segments constituting the ridge line are tensor product type curves here, mathematical accuracy can be maintained even if divided at an arbitrary point. Therefore, the subdivision in step S13 does not change the shape of the ridgeline. Further, by subdividing the points as described above, it becomes easier to associate the hypotenuse of the triangular patch with the segment to be newly generated in the subsequent processing. In step S11, a connection control point that is a segment connection point is newly generated, and the position of the conventional internal control point is also changed and a new internal control point is generated. Accordingly, as shown in FIG. 5C, the position coordinates of the new control point and the parameter value t in the parameter space T with respect to the ridge line are stored in the segment data storage unit of the hybrid patch storage unit 15. In FIG. 5C, the distinction between the connection control point and the internal control point is not registered, but there are two internal control points between the two connection control points. If they are arranged in the order of t, they can be specified.

Then, the hybrid patch conversion unit 13 performs a ridge line deviation removal process (step S15). This ridge line deviation removal process will be described with reference to FIG. FIG. 7 is an enlarged view of a part of FIG. 6. The segment 102 is subdivided into segments 1021, 1022 and 1023 by segment connection points 163a and 164a newly generated in step S13. . In the example of FIG. 7, the segment 1021, the segment 1022, and the segment 1023 are straight lines. In this case, not only the connection control point that is the segment connection point but also the internal control points exist on the segment 1021, the segment 1022, and the segment 1023. That is, the internal control points 181 and 182 exist between the end point 104a of the segment 1021 and the segment connection point 163a, and the internal control points 184 and 185 exist between the segment connection points 163a and 164a of the segment 1022. An internal control point 185 exists next to the segment connection point 164a of the segment 1023. The internal control points are also generated when the ridge line is subdivided in step S13. These data are stored in FIG. It should be noted that the end point 104a and the vertex 104 of the segment 1021 should coincide with each other, but are actually separated as shown in FIG. Since C ⁰ continuity cannot be guaranteed if they are separated in this way, the end point 104a of the segment 1021 is moved to the position of the vertex 104 in step S15. However, if only the end point 104a is moved, a problem may occur such that the segment 1021 defined by the end point 104a, the segment connection point 163a, and the internal control points 181 and 182 may be sharply curved. The positions of 181 and 182 are also adjusted. That is, the position of the internal control point 181 is moved to the position of the point 181a so that the segment 1021 changes smoothly, and the position of the internal control point 182 is moved to the position of the point 182a. By such processing, the divergence between the vertex and the ridge line is removed. In the present embodiment, the divergence is removed by giving priority to the vertex over the ridgeline. For the coordinate positions of the end point 104a and the internal control points 181 and 182, the changed values are registered in the segment data storage unit of the hybrid patch storage unit 15.

  Then, the hybrid patch conversion unit 13 performs a quadrilateral patch (transition quadrilateral) within a portion included in the patch segment 150 to be trimmed by the ridgeline (that is, within the portion excluding the base patch region of the segment 150). A storage process of a patch is performed (step S17). This process will be described with reference to FIGS. Based on the parameter constant line generated in steps S5 and S9 and the intersection calculated in steps S7 and S11, the hybrid patch conversion unit 13 has a quadrilateral shape in the portion included in the surface portion 150 of the patch trimmed by the ridgeline. The patch is specified as a transition quadrilateral patch (FIG. 8: Step S21). FIG. 9 shows the transition quadrilateral patch specified in the case of FIG. In the example of FIG. 9, the transition quadrilateral patches B1 and B2 are included in the patch B, the transition quadrilateral patches C1 to C9 are included in the patch C, and the transition quadrilateral patches G1 to G3 are included in the patch G. Since there are transition quadrilateral patches P1 to P6, the transition quadrilateral patches are specified. As described above, the original patch of the Bezier-type composite curved surface 200 is subdivided by the parameter constant line and the ridge line equivalent line as described above. Product surface can be subdivided mathematically and accurately. Adjacent patches after subdivision share their control points and maintain continuity.

  Among the identified transition quadrilateral patches, there is also a transition quadrilateral patch that includes a point on the ridge line equivalent line as a vertex. For such a transition quadrilateral patch, the vertex is moved so that the vertex is on the ridge line (step S23). That is, the point on the ridge line equivalent line (that is, the vertex of the transition quadrilateral patch) is moved to the segment connection point generated in step S13. This state will be described with reference to FIGS. 10 and 11 which are oblique views from the direction of the arrow 300 in FIG. The state before step S23 is shown in FIG. In FIG. 10, there is a divergence between the segments 1023 and 1024 that are ridge lines and the surface segment 150, and the segment connection points (connection control points) generated in step S13 are points 164a, 165a, and 166a. Internal control points 185 and 186 exist between segment connection point 164a and segment connection point 165a, which are connection control points, and internal control points 187 and 188 exist between segment connection point 165a and segment connection point 166a. Existing. The triangular patches C11 and D1 are used in later processing. In the range shown in FIG. 10, the transition quadrilateral patch is only C1, and the vertex 165 of this transition quadrilateral patch C1 is a point on the ridge line equivalent line. As can be seen from FIG. Similarly, the vertex 166 is a point on the ridge line equivalent line of the transition quadrilateral patch not shown in FIG. Accordingly, the vertex 164 is moved to the segment connection point 164a, the vertex 165 is moved to the segment connection point 165a, and the vertex 166 is moved to the segment connection point 166a. The state after the process of step S23 is shown in FIG. In FIG. 11, vertices 164, 165, and 166 have moved to the positions of segment connection points 164a, 165a, and 166a, respectively. Therefore, the control point representing the line segment connected to the vertex 164 of the transition quadrilateral patch C1 should also be at a position where the line segment changes smoothly. In FIG. 11, for example, the internal control points 191 and 192 are moved downward in the drawing according to the movement of the vertex 164. 10 and 11, the control points are shown for both the triangular patch and the quadrilateral patch. However, the control points are illustrated to show that the positions of some control points move and the patch shape changes. Therefore, it is not always necessary to specify the control point at the stage of step S23.

  Returning to the description of FIG. 8, the hybrid patch conversion unit 13 stores the data of the transition quadrilateral patch in the hybrid patch storage unit 15 (step S25). Since the shape of the transition quadrilateral patch is also specified in steps S21 and S23, the parameter values in the parameter space for the Bezier composite curved surface 200 (basic curved surface) at the two diagonal connection points of the transition quadrilateral patch, The coordinate values of (16) control points can be determined. These data are stored in the transition quadrilateral patch area data storage section of the transition area data storage section shown in FIG. In the example of FIG. 5B, the diagonal connection point 1 column storing the parameter values of the first diagonal connection point of the transition quadrilateral patch in the (U, V) space with respect to the base curved surface is the same as the diagonal line. A sequence of connection points 2, a sequence of control points 1 storing the coordinate values of the first control point among the 16 control points of the transition quadrilateral patch,. . . It includes a row of control points 16 for storing the coordinate values of the 16th control point among the 16 control points of the transition quadrilateral patch, and a row of pointers. The transition quadrilateral patches are arranged in the V direction around the loop from the loop to the base patch or the ridge line equivalent line. In the example shown in FIG. 9, B2, B1, C9, C7, C4, C8, C6, C3, C5, C2, C1, G3, G2, G1, P6, P5, P3, P4, P2, P1 in this order. be registered.

  In the example shown in FIG. 9, all transition quadrilateral patches collide with the base patch when viewed from the ridge line equivalent line, but in the case shown in FIG. 12, searching for the transition quadrilateral patch from the ridge line equivalent line corresponds to the ridge line. There will be a part that will hit the line. In FIG. 12, the patch Q and the patch R are base patches, and the transition quadrilateral patches S1 and S2 collide with the base patch when searched in the V direction (vertical direction). However, the transition quadrilateral patches X1 to X4 do not collide with the base patch when searching in the V direction. The same applies to the transition quadrilateral patches Y1 and Y2. In such a case, the transition quadrilateral patch X1 adjacent to the ridge line equivalent line to the transition quadrilateral patch X4 so that the transition quadrilateral patches X1 to X4 can be traced from either the segment 301 or the segment 302. A pointer and a pointer from the transition quadrilateral patch X4 to the transition quadrilateral patch X1 are provided. Similarly, a pointer for transition between the transition quadrilateral patches Y1 and Y2 adjacent to the ridge line equivalent line is also provided.

After performing such processing, the process returns to the processing flow of FIG. The hybrid patch conversion unit 13 is a triangular patch (referred to as a transition quadrilateral patch) within a portion included in the surface segment 150 of the patch trimmed by the ridgeline (that is, within a portion excluding the base patch region of the surface segment 150). ) Is executed (step S19). This process will be described with reference to FIGS. Based on the parameter constant line generated in steps S5 and S9 and the intersection calculated in steps S7 and S11, the hybrid patch conversion unit 13 creates a triangular patch in the portion included in the surface portion 150 of the patch trimmed by the ridgeline. Is identified as a transition triangle patch (FIG. 13 : step S 31 ). Transition triangle patches specified in the case of FIG. 5 are patches B11, C11, C12, C13, C14, D11, G11, F11, P11, and P12, as shown in FIG. As described above, adjacent triangular patches and quadrilateral patches after subdivision share their control points and maintain continuity.

  In the example of FIG. 9, the hypotenuses of all the transition triangle patches exist on the ridge line equivalent line. The hypotenuse of the transition triangle patch is moved to the corresponding segment of the ridge line (step S33). As shown in FIG. 11, the vertex is matched with the ridge line, but the ridge line equivalent line corresponding to the hypotenuse of the transition triangle patch and the ridge line are deviated from the state shown in FIG. 14. In FIG. 14, the ridge line equivalent line shown in FIG. 11 is indicated by a dotted line, and the hypotenuse of the transition triangle patch is moved so as to coincide with the corresponding segment of the ridge line. That is, the internal control points 185 and 186 of the segment 1023 are control points on the hypotenuse of the transition triangle patch C11. Similarly, the internal control points 187 and 188 of the segment 1024 are control points on the hypotenuse of the transition triangle patch D11. In addition, although processing like step S33 was implemented about the transition triangle patch, depending on the case, the process which makes the edge correspond to the segment of a ridgeline may be implemented about a transition quadrilateral patch.

Then, the hybrid patch conversion unit 13 stores the transition triangle patch data in the hybrid patch storage unit 15 (step S35). Since the shape of the transition triangle patch is also identified by steps S31 and S33, the parameter values in the parameter space (U, V) of the vertices at both ends of the hypotenuse of the transition triangle patch with respect to the Bezier composite curved surface 200 (basic curved surface); It is possible to determine the coordinate values of all (10) control points and the parameter values in the parameter space T for the ridgeline (Bézier system complex curve) of the ridgeline segment corresponding to the hypotenuse of the transition triangle patch. These data are stored in the transition triangle patch area data storage section of the transition area data storage section shown in FIG. In the example of FIG. 5B, in the parameter space T for the first vertex that is one end of the hypotenuse of the transition triangle patch in the parameter space (U, V) for the base curved surface and the ridgeline (Bézier system complex curve). A column of vertices 1 for storing parameter values, a parameter value for the second vertex that is the other end of the hypotenuse of the transition triangle patch in the parameter space (U, V) for the base curved surface, and a parameter for the edge line (Bézier complex curve) A column of vertices 2 that stores parameter values in space, a column of control points 1 that stores the coordinate values of the first control point of the 10 control points of the transition triangle patch,. . . And a column of control points 10 storing the coordinate values of the 10th control point among the 10 control points of the transition triangle patch. The transition quadrilateral patches are arranged around the loop, and in the example shown in FIG. 9, they are arranged in the order of B11, C14, C13, C12, C11, D11, G11, F11, P12, and P11. The reason why the parameter values t of the vertices at both ends of the hypotenuse in the parameter space with respect to the ridgeline is held is to make it easier to trace the intersection line when the surface segment 150 is cut. That is, when tracing the intersection line between transition triangle patches, searching for a parameter section in the parameter space T with respect to the ridge line can identify patches facing each other across the ridge line. Incidentally, in the case of a quadrangular patch, the parameter section of the parameter space (U, V) for the base curved surface is searched. Again, because of the tensor product type compound curved surface and compound curve, any curve at the boundary of one patch can be mathematically accurately cut, and two adjacent patches share a control point. Since the ^C0 connection is guaranteed, the property that there is a point corresponding to an adjacent patch is used.

By performing the processing as described above, the ridge line equivalent line that is the boundary of the surface segment 150 becomes coincident with the segment of the ridge line, and the end point of the segment also coincides with the vertex. The divergence between the ridgeline and the vertex is removed. That is, since the continuity of C ⁰ can be maintained, it is possible to perform graphic operations regardless of the tolerance. Further, the figure calculation does not stop for the offset curved surface due to the tolerance. In the present embodiment, cell complex expression is not performed. This is because the data structure of this embodiment is simpler and the amount of data is smaller than the cell complex representation.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this. Although a specific figure shape has been described as an example, application is not limited to such a figure shape. Moreover, although the example which performs sequentially about a processing flow was shown, the part which can be processed in parallel also exists. There are also steps that can be executed in a different order. As long as the main point of the processing described above is not changed, the order of processing can be changed.

  In addition, the base graphic conversion unit 9, the hybrid patch conversion unit 13, and the base patch conversion unit 17 may be configured to perform processing dynamically as necessary. As a result, the processing can be limited to patches that are involved in surface segment cutting, which is an internal processing of graphic computation, and the processing speed can be increased and the storage capacity can be saved. In addition, the format conversion unit 5 may use a method of generating general-purpose intermediate data and then converting it, or a method of converting directly.

(Appendix 1)
The base patch that is not trimmed by the Bezier composite curve is identified from the surface segments obtained by trimming the Bezier composite curved surface with the Bezier composite curve, and the data of the base patch is stored in the graphic data storage unit. And steps to
Of the patch to be trimmed by the Bezier composite curve among the Bezier composite curved surface, a portion included in the surface segment is a quadrilateral patch and a triangle according to a predetermined rule using a parameter constant line determined from the base patch. A splitting step to split the patch,
Of the vertices of the quadrilateral patch and the triangular patch, the vertex that becomes the boundary of the face is a corresponding point on the Bezier system composite curve, and the side that becomes the boundary of the face of the triangle patch is the edge Move to the corresponding part of the Bezier complex curve, and store the data of the quadrilateral patch and the triangle patch after the movement processing in the graphic data storage unit,
Graphic data conversion processing method.

(Appendix 2)
2. The graphic data according to claim 1, wherein in the dividing step, the division is further performed using a parameter constant line obtained from a parameter value of a point on the surface corresponding to the segment connection point of the Bezier composite curve. Conversion processing method.

(Appendix 3)
The graphic data conversion processing according to claim 1 or 2, wherein in the dividing step, the division is further performed by using a constant parameter line obtained from a parameter value at an intersection of the boundary line of the surface and the constant parameter line. Method.

(Appendix 4)
The graphic data conversion process according to any one of appendices 1 to 3, wherein the constant parameter line determined from the base patch is a constant parameter line obtained from a parameter value of a connection control point of the base patch. Method.

(Appendix 5)
The moving step comprises:
Additional steps 1 to 4 further comprising the step of further dividing the Bezier composite curve at a point on the Bezier composite curve corresponding to a vertex serving as a boundary of the face segment among the vertices of the quadrilateral patch and the triangle patch. The graphic data conversion processing method according to any one of the above.

(Appendix 6)
The moving step comprises:
When there is a divergence between the point defined as the vertex of the surface and the Bezier compound curve, the segment related to the point of the Bezier compound curve is modified to pass through the point. The graphic data conversion processing method according to any one of appendices 1 to 5.

(Appendix 7)
The supplementary note, wherein at least one of the base patch data and the quadrilateral patch data includes a parameter value and coordinate values of all control points on the Bezier composite curved surface of the diagonal connection point. The graphic data conversion processing method according to any one of 1 to 6.

(Appendix 8)
The triangular patch data includes the parameter values in the Bezier-based composite curved surface and the parameter values in the related segment of the Bezier-based composite curve, and the coordinate values of all control points at the vertices of the hypotenuse of the triangular patch. The graphic data conversion processing method according to any one of supplementary notes 1 to 7, characterized by comprising:

(Appendix 9)
The supplementary note 1 to 8, wherein the base patch is managed according to a parameter value in the Bezier composite curved surface, and the triangular patch and the quadrilateral patch are managed in a loop direction by the Bezier composite curve. Graphic data conversion processing method described in one.

(Appendix 10)
The base patch that is not trimmed by the Bezier composite curve is identified from the surface segments obtained by trimming the Bezier composite curved surface with the Bezier composite curve, and the data of the base patch is stored in the graphic data storage unit. And steps to
Of the patch to be trimmed by the Bezier composite curve among the Bezier composite curved surface, a portion included in the surface segment is a quadrilateral patch and a triangle according to a predetermined rule using a parameter constant line determined from the base patch. A splitting step to split the patch,
Of the vertices of the quadrilateral patch and the triangular patch, the vertex that becomes the boundary of the face is a corresponding point on the Bezier system composite curve, and the side that becomes the boundary of the face of the triangle patch is the edge Move to the corresponding part of the Bezier complex curve, and store the data of the quadrilateral patch and the triangle patch after the movement processing in the graphic data storage unit,
A graphic data conversion program that allows a computer to execute.

(Appendix 11)
The base patch that is not trimmed by the Bezier composite curve is identified from the surface segments obtained by trimming the Bezier composite curved surface with the Bezier composite curve, and the data of the base patch is stored in the graphic data storage unit. Means to
Of the patch to be trimmed by the Bezier composite curve among the Bezier composite curved surface, a portion included in the surface segment is a quadrilateral patch and a triangle according to a predetermined rule using a parameter constant line determined from the base patch. A dividing means for dividing the patch;
Of the vertices of the quadrilateral patch and the triangular patch, the vertex that becomes the boundary of the face is a corresponding point on the Bezier system composite curve, and the side that becomes the boundary of the face of the triangle patch is the edge Moving to a corresponding part of the Bezier-type compound curve, and storing the data of the quadrilateral patch and the triangle patch after the moving process in the graphic data storage unit;
A graphic data conversion apparatus.

(Appendix 12)
A data structure representing a surface segment obtained by trimming a Bezier compound curved surface with a Bezier compound curve,
A data structure for a base patch group that is not trimmed by the Bezier composite curve among the surface segments, and a parameter value and all of the diagonal connection points for each base patch in the Bezier composite surface Including a coordinate value of a control point, a data structure for managing the base patch group in order of parameter values in the Bezier composite curved surface;
Of the patch that is trimmed by the Bezier composite curve among the Bezier composite curved surface, a portion included in the surface corresponds to a parameter constant line determined from the base patch and a segment connection point of the Bezier composite curve. Dividing according to a predetermined rule using a parameter constant line obtained from a parameter value of a point on the surface segment, a parameter constant line obtained from a parameter value of an intersection of the boundary line of the surface segment and the parameter constant line A data structure for a quadrilateral patch group obtained by the step, wherein each quadrilateral patch includes parameter values and coordinate values of all control points on the Bezier-based composite curved surface of diagonal connection points, and the quadrilateral patch A data structure for managing groups in the order of the loop direction of the Bezier complex curve;
Of the patch that is trimmed by the Bezier composite curve among the Bezier composite curved surface, a portion included in the surface corresponds to a parameter constant line determined from the base patch and a segment connection point of the Bezier composite curve. Dividing according to a predetermined rule using a constant parameter line obtained from a parameter value of a point on the surface segment, a constant parameter line obtained from a parameter value of an intersection of the boundary line of the surface segment and the constant parameter line Is a data structure for a triangular patch group obtained by the following: a parameter value in the Bezier composite curved surface and a parameter value in a related segment of the Bezier composite curve at the vertices of the hypotenuse of the triangular patch, The triangular patch group in the order of the loop direction of the Bezier compound curve. And a data structure for management,
A data structure containing

(Appendix 13)
A data structure representing a surface segment obtained by trimming a Bezier compound curved surface with a Bezier compound curve,
A data structure for a base patch group that is not trimmed by the Bezier complex curve among the surface segments, including data for specifying each base patch, and for managing the base patch group Data structures and
Of the patch that is trimmed by the Bezier composite curve among the Bezier composite curved surface, a portion included in the surface segment is obtained by dividing the portion according to a predetermined rule using a constant parameter line determined from the base patch. A data structure for a quadrilateral patch group and a triangular patch group, the data structure including data for identifying each quadrilateral patch and each triangular patch, and a data structure for managing the quadrilateral patch group; and A data structure including a data structure for managing a group of triangular patches;
A data structure containing

(Appendix 14)
Data of the Bezier composite curve modified so that a point on the Bezier composite curve corresponding to a vertex serving as a boundary of the face segment among the vertices of the quadrilateral patch and the triangle patch becomes a further segment connection point. 14. The data structure according to appendix 12 or 13, further including:

(Appendix 15)
When there is a divergence between the point defined as the vertex of the ridge line and the Bezier composite curve in the data of the Bezier composite curve, the segment related to the point of the Bezier composite curve passes the point 15. The data structure according to appendix 14, wherein the data structure is modified to

It is a figure for demonstrating the problem of a prior art. It is a functional block diagram concerning one embodiment of the present invention. It is a flowchart which shows the main process flow in one embodiment of this invention. It is a schematic diagram of a figure shape. (A) is an example of data stored in the base patch data storage unit, and (b) is stored in a transition region data storage unit including a transition quadrilateral patch region data storage unit and a transition triangle patch region data storage unit. (C) shows an example of data stored in the segment data storage unit. It is a figure which shows typically the figure shape containing a parameter fixed line. It is a figure for demonstrating a ridgeline deviation removal process. It is a figure which shows the processing flow of the storage process of a transition quadrilateral patch. It is a figure for demonstrating arrangement | positioning of the patch in a transition area | region. It is a perspective view which shows the deviation of a transition quadrilateral patch and a transition triangle patch, and a ridgeline. It is a figure for demonstrating the movement of the vertex of a transition quadrilateral patch and a transition triangle patch. It is a figure for demonstrating the pointer of a transition quadrilateral patch area | region data storage part. It is a figure which shows the processing flow of the storage process of a transition triangle patch. It is a figure for demonstrating the movement of the hypotenuse of a transition triangle patch.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 CAD-A system 3 CAD-A data storage part 5 Format conversion part 7 B spline system CAD data storage part 9 Base figure conversion part 11 Bezier system CAD data storage part 13 Hybrid patch conversion part 15 Hybrid patch storage part 17 Base patch conversion Part 19 Graphical computation part

Claims (4)

A graphic data conversion processing method executed by a computer having a patch conversion unit and a graphic data storage unit,
The patch conversion unit identifies a base patch that is not trimmed by the Bezier composite curve from among the surface segments obtained by trimming a Bezier composite curved surface with a Bezier composite curve, and sets the base patch data. and storing the graphic data storage section,
A portion of the Bezier-based composite curved surface that is trimmed by the Bezier-based composite curve by the patch conversion unit, and a portion included in the surface segment is determined using a predetermined parameter line determined from the base patch. Splitting into quadrilateral and triangular patches according to:
The patch conversion unit converts a vertex of the quadrilateral patch and the triangle patch into a corresponding point on the Bezier composite curve to a vertex corresponding to the surface segment of the triangle patch. A moving step of moving a side to be a boundary to a corresponding part of the Bezier compound curve, and storing data of the quadrilateral patch and the triangular patch after the moving process in the graphic data storage unit,
Graphic data conversion processing method.   2. The figure according to claim 1, wherein in the dividing step, the division is further performed using a parameter constant line obtained from a parameter value of a point on the surface corresponding to a segment connection point of the Bezier compound curve. Data conversion processing method. The moving step comprises:
The step of further dividing the Bezier-based composite curve at a point on the Bezier-based composite curve corresponding to a vertex serving as a boundary of the face segment among the vertices of the quadrilateral patch and the triangular patch. The graphic data conversion processing method described. The base patch that is not trimmed by the Bezier composite curve is identified from the surface segments obtained by trimming the Bezier composite curved surface with the Bezier composite curve, and the data of the base patch is stored in the graphic data storage unit. And steps to
Of the patch to be trimmed by the Bezier composite curve among the Bezier composite curved surface, a portion included in the surface segment is a quadrilateral patch and a triangle according to a predetermined rule using a parameter constant line determined from the base patch. A splitting step to split the patch,
Of the vertices of the quadrilateral patch and the triangular patch, the vertex that becomes the boundary of the face is a corresponding point on the Bezier system composite curve, and the side that becomes the boundary of the face of the triangle patch is the edge Move to the corresponding part of the Bezier complex curve, and store the data of the quadrilateral patch and the triangle patch after the movement processing in the graphic data storage unit,
A graphic data conversion program that allows a computer to execute.

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