JPH0844906A - Surface model generating method - Google Patents

Abstract

PURPOSE:To automatically generate a surface model by generating a closed loop by repeating operation wherein an edge of a wire frame model which has an end point within a set error range is recognized as a continuous edge and continuous edges containing a maximum or minimum angle are connected. CONSTITUTION:It is recognized that plural edge of the wire frame model having an end point in the set error range are continuous, and the edge is projected on a reference coordinate plane to generate a mapping model. When the operation for connecting pairs of specific continuous edges and other edges which contain the maximum or minimum angle is repeated in a specific direction, the other end point of the specific edge is reached to form the closed loop. According to characteristics of the generated closed loop, a surface in a specific shape is generated. For example, when the closed loop is on a plane of the original wire frame, the surface is defined by the mathematical expression showing the plane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface model generation method for automatically generating a surface model from a wire frame model generated by CG or CAD.

[0002]

2. Description of the Related Art In order to execute various analyzes such as stress analysis using a finite element method (FEM) on an arbitrary wire frame model generated by CG or CAD,
You must define surface attributes such as whether the area enclosed by the wire is a flat surface or a curved surface. The finite element method divides a continuum into a finite number of small parts (hereinafter referred to as a "mesh"), approximates the characteristics of each element with an element equation, and combines them to form an overall model and solve them. Therefore, it cannot be divided into meshes unless the surface attribute is defined.

In addition, the wire frame model described above is CR
When displaying the layout on a display medium such as T to design the layout of the structure, for example, the layout design of each element in the engine room of an automobile, the positional relationship of each element cannot be determined unless the surface shape is clear. Accurate design becomes difficult.

Therefore, conventionally, an operator visually observes a wire frame model displayed on a display medium such as a CRT, and the wires (hereinafter, referred to as "edges") forming a closed loop are individually pointed by a mouse or the like. The device was selected and operated, and a surface of a predetermined shape was defined and generated according to the characteristics of the selected closed loop. That is, if the selected closed loop is on a plane, the surface is defined by a mathematical expression that indicates a plane, and if the selected closed loop is on a ruled surface, the surface is defined by a mathematical expression that indicates a ruled surface. If is on a free-form surface, the surface was defined by a mathematical expression (spline function) indicating the free-form surface. Here, the free-form surface is generated by, for example, complementing a curve network formed by a plurality of spline curves by a technique such as Coons blending, or a quadrilateral region forming a closed loop is defined as a unit region. As NURBS (Non Unifo
rm Relational B-Spline) Generated as a curved surface.

[0005]

However, in the above-mentioned conventional technique, the operator selects and operates each wire (hereinafter, referred to as "edge") forming a closed loop while observing the wire frame model. Because it was a thing,
If the wire frame model has a complicated three-dimensional shape, the frequency of selection operations increases, which requires a long and complicated operation, which not only causes a great deal of fatigue to the operator, but sometimes it takes several months to generate all surfaces. There was a problem that it took a huge amount of time. Furthermore, in the case of a complicated wire frame model, the operation of selecting an edge forming a closed loop, such as where the surface is, may be extremely difficult in some cases, and there is a problem that the operation requires skill. An object of the present invention is to solve the above-mentioned conventional drawbacks and to provide a surface model generation method for automatically generating a surface model from a generated wire frame model without manual operation.

[0006]

To achieve this object, the first characteristic configuration of the surface model generating method according to the present invention is such that the end points of the generated wire frame model are within the setting error range. Recognize a plurality of edges as continuous edges, generate a mapping model obtained by projecting them on the reference coordinate plane, and connect the edges that form the minimum or maximum angle between two consecutive edges in a predetermined rotation direction. The point is that a closed loop is generated by repeating along with, and a surface having a predetermined shape is generated according to the characteristics of the generated closed loop.

The second characteristic configuration is that, from the generated wire frame model, an edge having both end points where no other end points exist within the range of the first setting error, and the length between the end points is greater than the set length. The first step of deleting the small edge, the second step of recognizing the edge within the range of the second setting error as the overlapping edge, and deleting the overlapping part from one edge, and the plurality of edges 3rd step of dividing each edge so that the intersection becomes a new end point, and the end point is within the range of the 4th setting error with respect to the wire frame model that has gone through the third step. A plurality of edges in 1 are recognized as continuous edges, a mapping model obtained by projecting them on the reference coordinate plane is generated, and an operation of connecting the edges at which the angle formed by two continuous edges is minimum or maximum is specified. rotation Generating a closed loop by repeating along the direction lies in comprising a fourth step of generating a surface having a predetermined shape according to the characteristics of the generated closed loop.

A third characteristic configuration is that, from the generated wire frame model, an edge having both end points where no other end points exist within the range of the first setting error, and the length between the end points is greater than the set length. The first step of deleting the small edge, the second step of recognizing the edge within the range of the second setting error as the overlapping edge, and deleting the overlapping part from one edge, and the plurality of edges The third step of dividing each edge so that the intersection becomes a new end point, and the end point is within the range of the third setting error for the wire frame model that has gone through the third step. A plurality of edges in 1 are recognized as continuous edges, a mapping model obtained by projecting them on the reference coordinate plane is generated, and an operation of connecting the edges at which the angle formed by two continuous edges is minimum or maximum is specified. rotation The fourth step of generating a closed loop by repeating along the direction and generating a surface of a predetermined shape according to the characteristics of the generated closed loop, and an arbitrary point on the boundary of the adjacent surface generated in the fourth step. If the distance between them is within the range of the fourth setting error, there is a fifth step of forming a continuum.

A fourth characteristic configuration is that, from the generated wire frame model, an edge having both end points where other end points do not exist within the range of the first setting error, and a length between the end points is greater than the set length. The first step of deleting the small edge, the second step of recognizing the edge within the range of the second setting error as the overlapping edge, and deleting the overlapping part from one edge, and the plurality of edges The third step of dividing each edge so that the intersection becomes a new end point, and the end point is within the range of the third setting error for the wire frame model that has gone through the third step. A plurality of edges in 1 are recognized as continuous edges, a mapping model obtained by projecting them on the reference coordinate plane is generated, and an operation of connecting the edges at which the angle formed by two continuous edges is minimum or maximum is specified. rotation A fourth step that creates a closed loop by iterating along the direction, creating a surface of a given shape depending on the characteristics of the created closed loop, and other surfaces within the specific surface created in the fourth step. On the boundary of the adjacent surface generated in the fourth step, trimming the specific surface with the other surface and deleting the other surface when it is determined that If the distance between arbitrary points is within the range of the fourth setting error, it is a point including the sixth step of forming a continuum.

[0010]

[Operation] The operation of the first characteristic configuration will be described. Recognize that a plurality of edges related to other end points within the setting error range with respect to the end points of the generated wireframe model are continuous (usually, the connection points of each edge that configures the wireframe model, That is, the coordinates of the respective end points do not match and are slightly displaced), and a mapping model obtained by projecting onto the reference coordinate plane (for example, the xy plane) is generated, and two consecutive edges, that is, the specified By repeating the operation of connecting the pair of edges having the minimum or maximum angle formed by the edge of 1 and the other edge along the predetermined rotation direction, the closed loop is generated by reaching the other end point of the specific edge. A surface having a predetermined shape is generated according to the characteristics of the generated closed loop. If the generated closed loop is on a plane in the original wireframe model, the surface is defined by a mathematical expression that indicates a plane, and if it is on a ruled surface, the surface is defined by a mathematical expression that indicates a ruled surface. For example, a surface is defined by a mathematical expression that represents a free-form surface.

According to the second feature configuration, before the method according to the first feature configuration is executed, the endpoints of the generated wireframe model where other endpoints do not exist within the range of the first setting error are determined. It recognizes an edge that it has as an isolated single element and deletes it because the existence of the single element hinders the generation of a closed loop. The existence of an edge whose length between the end points is smaller than the set length hinders the generation of the free-form surface and causes an analysis error by the finite element method which will be described later. Furthermore, if there are other edges, etc. that actually overlap in the vicinity of a specific edge but are numerically subtly different, what should be expressed as a single surface will have extra minute surfaces formed or partially overlapped. Since it will form a surface to be formed, delete this, find the intersection between the edges, and divide each edge so that the intersection becomes a new end point, and generate the minimum unit wireframe model To do.

According to the third characteristic configuration, the plurality of surfaces generated by the second characteristic configuration are independently defined, so that actually adjacent adjacent surfaces are discontinuous. In order to avoid the inconvenience of being treated as if it were, if the distance between arbitrary points on the boundary of the adjacent surface is within the range of the fourth setting error, it will be treated as a continuum, so that it can be analyzed later by the finite element method. This is to ensure the continuity of the nodes of the mesh generated in advance.

According to the fourth characteristic configuration, when the plurality of surfaces generated by the second characteristic configuration are overlapped with other surfaces in the specific surface, holes are formed in the specific surface. Is determined to have been formed,
The specific surface is trimmed with the other surface and the other surface is deleted.

[0014]

As described above, according to the present invention, it is possible to automatically generate a surface model from a generated wire frame model in a short time with certainty, which causes a great fatigue to an operator and requires skill. It is now possible to provide a surface model generation method that does not exist.

[0015]

EXAMPLES Examples will be described below. A computer that executes various analyzes such as stress analysis using the finite element method is generally 3
Consists of blocks. That is, a preprocessor that generates a model to be analyzed, a solver that executes analysis on the generated model, and data processing for displaying and outputting the data obtained as a result of the analysis in a graph with good visibility. It is a post processor that does.

That is, if a wire frame model generated by CG or CAD is provided as shown in FIG.
1>, the surface model is automatically generated by the preprocessor <# 2>, and the mesh used for analysis is automatically generated for the generated surface model.
Boundary conditions and analysis conditions are set to complete the analysis model <# 3>, <# 4>. The analysis model is analyzed by the finite element method with the solver <# 5>, and the post-processor performs data processing to output the analysis result with good visibility <# 6>. >.

Using the wire frame model as shown in FIG. 5A generated by CAD as an example, the above steps <#
The automatic generation of the surface model in 2> will be described based on the flowcharts shown in FIGS. 2 and 3.

The wire frame model is expressed as a set of a plurality of edges, that is, the coordinates of the end points and the attributes of the line segment connecting them (lines, arcs, and splines). In the CRT as shown in FIG. 4, the coordinates of the end points of the edges which seem to be continuous are actually slightly deviated as shown in FIGS. 4A and 4B. In the CRT as shown in (f), an edge that seems to be one may actually be a set of a plurality of overlapping edges as shown in (d) and (e) of FIG.

With respect to an arbitrary edge constituting the wire frame model, the preprocessor first has an edge having both end points within the range of the first setting error ε ₁ (FIG. 5A). (Auxiliary line L1 in FIG. 5) is extracted as a single element, and is deleted as shown in FIG. 5B, and an edge whose length between end points is smaller than the set length is deleted <# 11>, <# 12>. Here, the set length can be set to, for example, a length shorter than the average length of the edges constituting the wire frame model by one digit or more, but the setting is arbitrary.

Next, an edge within the range of the second setting error ε ₂ is recognized as an overlapping edge, and the overlapping portion is deleted from one edge <# 13>. For example, in the case of overlapping as shown in FIG. 4D, the overlapping part is deleted from one of the edges as shown in FIG. 4G, and the deleted part is generated as a new edge. When overlapping as shown in FIG. 4E, the overlapping portion is deleted from one of the edges as shown in FIG. 4H, and the deleted portion is generated as a new edge.

Further, the intersection point coordinates between the edges are obtained, the edge is divided with the intersection point as a new end point, and the surface generation described later can be performed in the minimum unit <# 14>. For example,
As shown in FIG. 6A, the edges L3, L4, and L5 are connected at their end points at P1, but when the other end point of the edge L3 intersects in the middle of the edge L2, the other edge L3 With respect to the end point, intersection coordinates are obtained between the edge and an edge existing within the range of the fifth setting error ε ₅ , and as shown in FIG. 6B, the edge L2 is the edge L21 and the edge L21.
It is divided into 22 and is connected to the edge L3 at P2. In other words, when the edges intersect, of course, the fifth setting error ε with respect to the end point even when the edges do not intersect.
Even if an edge exists within the range of ₅ , it is recognized that the edge intersects. After the intersection division processing is executed, a new minute length edge may occur, and therefore the processing returns to step <# 12> and the same processing is performed again.

With respect to the wire frame model thus processed, the distance between the end points is checked, and the value ε ₃ is set so that the adjacent end points are included in the third setting error ε ₃ . # 15>. FIG. 7 shows the set error ε
_The edge points of edges that include adjacent edge points within ₃ are highlighted, and the value of the third setting error ε ₃ depends on whether the object is a large-scale structure such as a bridge or an electronic circuit. It is a value that is appropriately set depending on whether it is a minute structure.

After that, the direction vector of the end points of all the edges (the contact direction at the end points of the edges) is created, and each edge is x.
Edge tables are created by sorting the yz coordinates in ascending order from the smallest value to the largest value <# 16>, <# 17>.

It is recognized that a plurality of edges whose end points are within the range of the third setting error ε ₃ are continuous with respect to the wire frame model, and xy is a standard coordinate plane, that is, a three-dimensional structure. Closed loop by repeating along a predetermined rotation direction an operation of projecting onto a plane, a yz plane, and a zx plane to generate a mapping model, and connecting the edges where the angle formed by two consecutive edges is minimum or maximum. To generate a surface having a predetermined shape according to the characteristics of the generated closed loop <# 18>, ..., <# 26>.

For example, as shown in FIG. 7, starting from an edge E1 where the x coordinate of the end point is small, the intersection point P1 is reached and P1 is reached.
And the end points of the three edges E1 to E3 are the third setting error ε.
When it is within the range of ₃ , it is judged to be continuous. here,
When there are multiple branches at the intersection p1, xy as shown in FIG.
Generate a mapping model projected on a plane and generate edges E1 and E
Compared angle theta ₁ and the edge E1 formed between the 2 and the angle theta ₂ formed by the E3, since towards the corner theta ₁ is less connects the edge E2 from the edge E1. By repeating such an operation counterclockwise, edges E1 → E2 → E4 → E5 → E1
Closed loop is constructed, and this is step <# 17>
By executing on all edges in sorted order, all possible closed loops are extracted. If the edges forming the maximum angle between the two edges are connected, the above operation is repeated clockwise.

If the generated closed loop is on the plane in the original wire frame model, the surface is defined by a mathematical expression indicating the plane as shown in FIG. ), The surface is defined by a mathematical formula showing the ruled surface, and if it is on a free-form surface,
As shown in, the surface is defined by a mathematical expression showing a free-form surface. Here, the ruled surface or the free-form surface is generated, for example, while complementing the internal surface shape from the edge. For the curve network formed by the spline curve of the edge, Coons blending, etc. NURBS (Non Uniform R) is used as a unit area for a quadrilateral area that is generated using the above method or constitutes a closed loop.
national B-Spline) curved surface.

When the generated closed loop is not a quadrilateral but a pentagon or more polygon, it is judged that the angle formed by the two tangents at the intersection is smaller than the sixth setting error.
Judge that the two edges are smoothly continuous 1
It is converged into a quadrangle by repeating the process of redefining the edge of the book. As a result, if the quadrilateral cannot be converged, a warning is displayed to the operator and the closed loop is further divided to prompt the creation of a new edge.

The above steps <# 18>, ..., <# 2
For all surfaces generated in 6>, determine whether other surfaces are duplicated in a specific surface based on whether the surface definition formulas are almost the same,
When it is determined that they overlap, the specific surface is trimmed with the other surface, and the other surface is deleted <# 27>, ..., <# 32>.

For example, when the surface S1 generated by the mapping model as shown in FIG. 8 overlaps the surface S2, the surface S2 is trimmed from the surface S1 and then the surface S2 is deleted.

Since the surface models generated as a result of the execution of the above steps are defined independently of each other, they are recognized as discontinuous surfaces even though they are actually continuous. Therefore, it is discriminated whether the distance between arbitrary points on the boundary of the adjacent surface is within the range of the fourth setting error ε ₄ , and if it is within the range of the error ε ₄ , it is recognized as a continuum, By replacing the formula of the boundary of one surface with the formula of the boundary of the other surface, surface continuity is guaranteed, and the surface model as shown in FIG. 10 is completed <# 33>.

As described above, the surface model is automatically generated from the wire frame model. In order to analyze the surface model thus generated by the finite element method, the above mesh generation program is started, As shown in FIG. 11, a mesh used for analysis is automatically generated <# 34>.

Another embodiment will be described below. Although the above-described fourth characteristic configuration has been described in detail in the above embodiment, it may be configured to automatically and continuously execute each step of the fourth characteristic configuration, or by the operator's instruction input. It may be configured such that each step is executed independently.

The surface model generating method according to the present invention may have the following configuration. That is, in the above-described fourth characteristic configuration, when it is determined that another surface is duplicated in the generated specific surface, the specific surface is trimmed with the other surface, and the other surface is Depending on the model, it may not be necessary to trim the overlapping surfaces when performing the step of deleting, so you may add an area specification step so that you can arbitrarily set the application area. The step may be removed as in the characteristic configuration.

Further, unless the analysis by the finite element method is performed on the basis of the surface model, it is not necessary to guarantee the continuity of the surface. If the distance between the points is within the range of the fourth setting error, the step of forming a continuum may be removed and the second characteristic configuration may be adopted.

If the wire frame model has no single element or overlapping edge from the beginning and is divided into the minimum unit of edges, the surface model can be easily constructed automatically by configuring the first feature structure. Since it is generated, it is sufficient when the wire frame model is displayed on a display medium such as a CRT to perform the layout design of the structure, for example, the layout design of each element in the engine room of the automobile.

The value of each error described in the above embodiment is not particularly limited, and may be appropriately set based on the scale of the wire model, the accuracy of the computer and the like.

[0037]

[Brief description of drawings]

FIG. 1 is a flowchart showing an analysis procedure using the finite element method.

FIG. 2 is a flowchart showing a surface model generation method.

FIG. 3 is a flowchart showing a surface model generation method.

FIG. 4 is an explanatory diagram of a main part

FIG. 5 is an explanatory diagram of a wire frame model.

FIG. 6 is an explanatory diagram of main parts

FIG. 7 is an explanatory diagram of a main part.

FIG. 8 is an explanatory diagram of mapping

[Figure 9] Illustration of surface attributes

[Figure 10] Illustration of surface model

FIG. 11 is an explanatory diagram of mesh division.

Claims (4)

[Claims] 1. A mapping model obtained by recognizing a plurality of edges whose end points are within a setting error range as a continuous edge in a generated wire frame model and projecting them on a reference coordinate plane, A closed loop is generated by repeating the operation of connecting the edges that form the minimum or maximum angle between the two edges along a predetermined rotation direction, and a surface of a predetermined shape is generated according to the characteristics of the generated closed loop. Surface model generation method. 2. From the generated wire frame model, an edge having both end points in which no other end points exist within the range of the first setting error, and an edge having a length between the end points smaller than the set length are set. The first step of deleting, the edge within the range of the second setting error are recognized as overlapping edges, the second step of deleting the overlapping part from one edge, and the intersection of multiple edges is obtained. , A third step of dividing each edge so that the intersection becomes a new end point, and a plurality of edges whose end points are within the range of the fourth setting error with respect to the wire frame model that has gone through the third step Is recognized as a continuous edge, a mapping model obtained by projecting onto the reference coordinate plane is generated, and an operation of connecting the edges where the angle formed by two continuous edges is minimum or maximum is connected along a predetermined rotation direction. Rounding A surface model generation method comprising a fourth step of generating a closed loop by returning, and generating a surface having a predetermined shape according to the characteristics of the generated closed loop. 3. From the generated wire frame model, an edge having both end points where other end points do not exist within the range of the first setting error, and an edge whose length between the end points is smaller than the set length are set. The first step of deleting, the edge within the range of the second setting error are recognized as overlapping edges, the second step of deleting the overlapping part from one edge, and the intersection of multiple edges is obtained. , A third step of dividing each edge so that the intersection becomes a new end point, and a plurality of edges whose end points are within the range of the third setting error for the wireframe model that has undergone the third step Is recognized as a continuous edge, a mapping model obtained by projecting onto the reference coordinate plane is generated, and an operation of connecting the edges where the angle formed by two continuous edges is minimum or maximum is connected along a predetermined rotation direction. Rounding By returning, the fourth step of generating a closed loop and generating a surface of a predetermined shape according to the characteristics of the generated closed loop, and the distance between arbitrary points on the boundary of the adjacent surface generated in the fourth step are A surface model generation method comprising a fifth step of forming a continuum within a range of a fourth setting error. 4. An edge having end points where no other end points exist within the range of the first setting error and edges whose length between the end points is smaller than the set length from the generated wire frame model. The first step of deleting, the edge within the range of the second setting error are recognized as overlapping edges, the second step of deleting the overlapping part from one edge, and the intersection of multiple edges is obtained. , A third step of dividing each edge so that the intersection becomes a new end point, and a plurality of edges whose end points are within the range of the third setting error for the wireframe model that has undergone the third step Is recognized as a continuous edge, a mapping model obtained by projecting onto the reference coordinate plane is generated, and an operation of connecting the edges where the angle formed by two continuous edges is minimum or maximum is connected along a predetermined rotation direction. Rounding By returning, a closed loop is generated, and a fourth step that generates a surface of a predetermined shape according to the characteristics of the generated closed loop, and if another surface overlaps with the specific surface generated in the fourth step If so, trim the particular surface with the other surface,
If the distance between arbitrary points on the boundary of the adjacent surface generated in the fourth step is within the range of the fourth setting error, the fifth step of deleting the other surface is regarded as a continuum. Surface model generation method consisting of