A simulation method of viscosity between thin membrane layers based on mass spring

Abstract

The present invention discloses a method for simulating the viscosity between thin membrane tissues based on a particle spring, and the present invention relates to the field of simulation technology. The method for simulating the viscosity between thin membrane tissues based on a particle spring simulates the viscosity between thin layer model tissues by constructing independent and complete membrane tissues and springs between two membrane tissues, thereby solving the problems of complex modeling and difficult physical simulation of strip-like or fibrous tissue structures, and realizing the simulation of I-shaped cutting in virtual anatomy and the skin flipping and peeling operations after cutting. This method can also be applied to the exploration and peeling simulation of blood vessels and nerves, improving a series of operations in virtual anatomy simulation, helping to reduce the cost of anatomy learning, and providing a more realistic, safe and effective anatomy practice environment for teachers and students of anatomy majors.

Description

Technical Field

[0001] The invention relates to the field of simulation technology, and in particular to a viscosity simulation method between membrane thin layer tissues based on a mass point spring. Background Art

[0002] With the development of computer technology and multidisciplinary integration technology, physical simulation technology has gradually been applied to fields such as education and medical treatment. Virtual anatomical simulation is an important application of physical simulation. Virtual anatomical simulation covers a wide range of content. In addition to the simulation of conventional pulling deformation, tissue structure cutting and shearing operations, an important content in virtual anatomical simulation is the peeling operation of membrane structures such as skin and fascia. In real anatomy, since fascia is a flocculent structure, it has the characteristics of complex modeling and difficult simulation. Therefore, a complete thin film structure can be constructed. By adding a connective tissue spring between the membrane structures, the viscosity between the thin membrane tissues based on the particle spring is simulated, which is applied to the peeling operation after the I-shaped cutting in the virtual anatomical physical simulation, providing a more realistic, safe and effective learning environment for medical students.

[0003] Among the existing relatively mature physical simulation simulators, most of them focus more on virtual simulation of minimally invasive surgery, such as laparoscopic or arthroscopic surgery simulation. The modeling and simulation of connective tissue between the liver and gallbladder in the common and relatively mature laparoscopic cholecystectomy training system is an important research topic. However, unlike the contact surface between the liver and gallbladder, in virtual local anatomy simulation, the judgment of the contact surface of membrane structures such as skin and fascia is more complicated. It is necessary to identify the inner and outer surfaces of the model, and then model the adhesion line of the connective tissue spring. The connection mapping method between the two layers of membrane structure is also an important technical problem that needs to be solved. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for simulating the viscosity between thin membrane layers based on a particle spring, which solves the problems mentioned in the above background technology.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a method for simulating the viscosity between thin membrane tissues based on a mass spring, specifically comprising the following steps:

[0006] S1, read the surface mesh of the membrane structure and generate a tetrahedral mesh;

[0007] S2, identify the vertices of the inner and outer surfaces of the membrane structure model;

[0008] S3. Add connections between membrane structures to simulate viscosity.

[0009] Preferably, in S1, a surface mesh model with a model texture is produced using 3D MAX modeling software, and a tetrahedral mesh model is generated based on the model to represent the internal structure and deformation of the model, and a physical simulation method based on PBD is used to perform model deformation simulation.

[0010] Preferably, the specific method is:

[0011] S11. Use 3DMAX modeling software to model the membranous tissue and save it as an OBJ format model;

[0012] S12, reading the model's vertices, faces, normals, textures and other information from the OBJ file, and displaying the model;

[0013] S13, using the vertex and face information of the surface mesh model, tetrahedralize the surface mesh model by using the tetrahedralize method of the tetgen library to generate a corresponding tetrahedral mesh model;

[0014] S14. Initialize the PBD system through the grid. In each time step, update the position and velocity of the particles according to the external forces and constraints to achieve conventional deformation simulation effects, providing a physical simulation basis for the realization of viscosity simulation between models.

[0015] Preferably, in S2, the specific operation steps are:

[0016] S21. Since the vertex order of the face in the model saved in OBJ format is generally counterclockwise and follows the right-hand screw rule, the normal direction of each triangle can be calculated from the positions of the three vertices: ;

[0017] In the formula, The normal vector of the triangle on the model that is currently being judged as the inner triangle face. , , are the coordinates of the three vertices of this triangle;

[0018] S22. For each triangular facet of the membrane structure, calculate whether the normal direction of the current triangular facet intersects with any triangular facet on the model. If there is a triangular facet that intersects with the normal direction of the current triangular facet, it is the inner side face, and the points on it are the inner surface vertices. Otherwise, it is the outer side face, and the corresponding vertices are the outer surface vertices. The remaining vertices are internal vertices generated by tetrahedronization.

[0019] Preferably, the method for determining the intersection of a normal line and a triangle is:

[0020] S22.1, if satisfied , the normal and the triangle are parallel and do not intersect, where: , , are the three vertices of the triangle;

[0021] In the formula, is the normal of any triangle on the model except the currently judged triangle, , , Respectively represent The components of the vector on the x-axis, y-axis, and z-axis, , , Respectively represent The components of the vector on the x-axis, y-axis, and z-axis, and the latter represent The component of the vector on the x-axis;

[0022] S22.2, otherwise, there is an intersection , further determine the position of the intersection point. If the intersection point is inside the triangle, it is considered that the normal line and the triangle intersect. The method for determining if a point is inside the triangle is as follows: ,in, , , , respectively , , , area;

[0023] The intersection point between the normal of the triangle to be judged as the inner triangle face and any other triangle. is any other triangle on the model except the one currently being judged to be the inner side triangle; a, b, c are the three vertices of the triangle , , The intersection point is three triangles composed of three vertices of the triangle.

[0024] Preferably, in S3, the steps of connecting the membrane structures and simulating the viscosity are as follows:

[0025] S31. The specific method of constructing the connection between the two models is to connect the inner side vertices of the outer layer model vertically to the outer side triangles of the inner layer model, thereby generating a series of viscosity lines;

[0026] S32, mass spring modeling, giving physical properties to the adhesion line;

[0027] S33. After the modeling display is completed, it can be applied to the corresponding local anatomical simulation operation. The adhesion line between two adjacent layers of film-like tissue is visualized and the particle spring method is used to add viscosity.

[0028] Preferably, in said S31, the specific construction method is:

[0029] S31.1. For each vertex on the outer model , draw a perpendicular line to the triangle face of the inner model, and if the foot of the perpendicular line is inside the triangle, return the foot of the perpendicular line and get the triangle , vertical foot The calculation method is:

[0030] ,

[0031] ,

[0032] ,

[0033] Where n=norm((t2-t1)*(t3-t1)), , , are the coordinates of the triangle vertices on the inner model, are the vertex coordinates on the outer model;

[0034] S31.2, select a perpendicular line with the shortest distance as the bonding line between the outer model vertex and the inner model;

[0035] S31.3. Since the end of the glue line can be located anywhere on the inner model triangle, the barycentric coordinates are used to mark the position of the end point on the triangle. The barycentric coordinates are calculated as follows: ,in, , , , respectively , , , area;

[0036] The end point of the bonding line on the inner model. The vertices of the triangle on the inner model; It is a triangle formed by point a, point b and point p; The triangle is composed of point a, point c, and point p; The triangle is composed of point b, point c, and point p; It is a triangle formed by points a, b, and c.

[0037] Preferably, in S32, the specific modeling method is:

[0038] S32.1. According to Hooke's law, calculate the elastic force between mass point i and mass point j, that is, and vertical foot Elastic force on:

[0039] ,

[0040] ,

[0041] in, is the elastic constant of the spring, is the existing length of the spring, Represents natural length; It is the endpoint of the bonding line on the outer model; is an endpoint of the glue line, that is, an endpoint on the outer model Elastic force on is the elastic force at the other end point P of the bonding line;

[0042] S32.2. Update the magnitude of the resultant force on the corresponding vertices on the model at both ends of the spring based on the elastic forces calculated at the two end points of the spring. The elastic forces at the perpendicular foot positions of the spring ends are transferred to the vertices of the triangle faces based on the coordinates of the center of gravity. Then, the velocities on the vertices are calculated and the positions of the vertices are updated. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of generating adhesion lines provided by the present invention;

[0044] Figure 2 This is a visualization diagram of the model grid plus bonding lines provided by the present invention.

[0045] Beneficial Effects

[0046] The present invention provides a method for simulating the viscosity between thin membrane tissues based on a particle spring. Compared with the prior art, the method has the following beneficial effects: the method for simulating the viscosity between thin membrane tissues based on a particle spring, by constructing an independent and complete membrane tissue and a spring between two membrane tissues, simulates the viscosity between thin layer model tissues, solves the problem of complex modeling and difficult physical simulation for strip-like or fibrous tissue structures, realizes the simulation of I-shaped cutting in virtual anatomy and the skin flipping and peeling operations after cutting, and can also be applied to the exploration and peeling simulation of blood vessels and nerves, improves a series of operations in virtual anatomy simulation, helps to reduce the cost of anatomy learning, and provides a more realistic, safe and effective anatomy practice environment for teachers and students of anatomy majors. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] A method for simulating viscosity between thin membrane tissues based on a mass spring specifically comprises the following steps:

[0049] S1. Read the surface mesh of the membrane structure and generate the tetrahedral mesh:

[0050] S11. Use 3DMAX modeling software to model the membranous tissue and save it as an OBJ format model;

[0051] S12, reading the model's vertices, faces, normals, textures and other information from the OBJ file, and displaying the model;

[0052] S13, using the vertex and face information of the surface mesh model, tetrahedralize the surface mesh model by using the tetrahedralize method of the tetgen library to generate a corresponding tetrahedral mesh model;

[0053] S14. Initialize the PBD system through the grid. In each time step, update the position and velocity of the particles according to the external forces and constraints to achieve the conventional deformation simulation effect, and provide a physical simulation basis for the realization of the viscosity simulation between models.

[0054] S2. Identify the vertices of the inner and outer surfaces of the membrane structure model:

[0055] S21. Since the vertex order of the face in the model saved in OBJ format is generally counterclockwise and follows the right-hand screw rule, the normal direction of each triangle can be calculated from the positions of the three vertices: ;

[0056] In the formula, The normal vector of the triangle on the model that is currently being judged as the inner triangle face. , , are the coordinates of the three vertices of this triangle;

[0057] S22, for each triangular face of the membrane structure, calculate whether the normal direction of the current triangular face intersects with any triangular face on the model; if there is a triangular face that intersects with the normal direction of the current triangular face, it is the inner side face, and the points on it are the inner surface vertices; otherwise, it is the outer side face, and the corresponding vertices are the outer surface vertices, and the remaining vertices are the inner vertices generated by tetrahedronization;

[0058] The way to determine the intersection of normal and triangle is:

[0059] S22.1, if satisfied , the normal and the triangle are parallel and do not intersect, where: , , are the three vertices of the triangle;

[0060] In the formula, is the normal of any triangle on the model except the currently judged triangle, , , Respectively represent The components of the vector on the x-axis, y-axis, and z-axis, , , Respectively represent The components of the vector on the x-axis, y-axis, and z-axis, and the latter represent The component of the vector on the x-axis;

[0061] S22.2, otherwise, there is an intersection , further determine the position of the intersection point. If the intersection point is inside the triangle, it is considered that the normal line and the triangle intersect. The method for determining if a point is inside the triangle is as follows: ,in, , , , respectively , , , area;

[0062] The intersection point between the normal of the triangle to be judged as the inner triangle face and any other triangle. is any other triangle on the model except the one currently being judged to be the inner side triangle; a, b, c are the three vertices of the triangle , , The intersection of the three triangles is composed of three vertices of the triangle;

[0063] S3. Add connections between membrane structures to simulate viscosity:

[0064] S31. The specific method of constructing the connection between the two models is to connect the inner side vertices of the outer layer model vertically to the outer side triangles of the inner layer model, thereby generating a series of viscosity lines;

[0065] The specific construction method is:

[0066] S31.1. For each vertex on the outer model , draw a perpendicular line to the triangle face of the inner model, and if the foot of the perpendicular line is inside the triangle, return the foot of the perpendicular line and get the triangle , vertical foot The calculation method is:

[0067] ,

[0068] ,

[0069] ,

[0070] Where n=norm((t2-t1)*(t3-t1)), , , are the coordinates of the triangle vertices on the inner model, are the vertex coordinates on the outer model;

[0071] S31.2, select a perpendicular line with the shortest distance as the bonding line between the outer model vertex and the inner model;

[0072] S31.3. Since the end of the glue line can be located anywhere on the inner model triangle, the barycentric coordinates are used to mark the position of the end point on the triangle. The barycentric coordinates are calculated as follows: ,in, , , , respectively , , , area;

[0073] The end point of the bonding line on the inner model. The vertices of the triangle on the inner model; It is a triangle formed by point a, point b and point p; The triangle is composed of point a, point c, and point p; The triangle is composed of point b, point c, and point p; It is a triangle formed by point a, point b, and point c;

[0074] So far, some properties of the glue line have been obtained, including the vertex index of the glue line on the outer model , connected to the triangle index on the inner model , the coordinates of the center of gravity of the triangle where the foot of the perpendicular is located ,like Figure 1 As shown;

[0075] S32, mass spring modeling, giving physical properties to the adhesion line;

[0076] The specific modeling method is:

[0077] S32.1. According to Hooke's law, calculate the elastic force between mass point i and mass point j, that is, and vertical foot Elastic force on:

[0078] ,

[0079] ,

[0080] in, is the elastic constant of the spring, is the existing length of the spring, Represents natural length; It is the endpoint of the bonding line on the outer model; is an endpoint of the glue line, that is, an endpoint on the outer model Elastic force on is the elastic force at the other end point P of the bonding line;

[0081] S32.2. Update the magnitude of the resultant force on the corresponding vertices on the model at both ends of the spring according to the elastic forces calculated at the two end points of the spring, wherein the elastic forces at the vertical foot positions of the end of the spring are respectively transmitted to the vertices of the triangle surface according to the coordinates of the center of gravity, and then calculate the velocity on the vertex, and finally update the position of the vertex;

[0082] S33. After the modeling display is completed, it can be applied to the corresponding local anatomical simulation operation. The adhesion line between two adjacent layers of thin film tissue is visualized and the viscosity is added by the particle spring method. Taking the skin and superficial fascia as an example, the viscosity performance after cutting the skin is as follows: Figure 2 shown.

[0083] Meanwhile, the contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0084] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0085] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for simulating the viscosity between thin membrane layers based on a mass spring, characterized in that: The specific steps include: S1. Read the surface mesh of the membrane structure and generate a tetrahedral mesh. Use 3D MAX modeling software to make a surface mesh model with model texture, and then generate a tetrahedral mesh model to represent the internal structure and deformation of the model. Use a physical simulation method based on PBD to simulate the model deformation, specifically: S11. Use 3DMAX modeling software to model the membranous tissue and save it as an OBJ format model; S12, reading the vertex, face, normal, and texture information of the model from the OBJ file, and displaying the model; S13, using the vertex and face information of the surface mesh model, tetrahedralize the surface mesh model by using the tetrahedralize method of the tetgen library to generate a corresponding tetrahedral mesh model; S14. Initialize the PBD system through the grid. In each time step, update the position and velocity of the particles according to the external forces and constraints to achieve the conventional deformation simulation effect, and provide a physical simulation basis for the realization of the viscosity simulation between models. S2. Identify the vertices of the inner and outer surfaces of the membrane structure model. The specific steps are as follows: S21. Since the vertex order of the face in the model saved in OBJ format is counterclockwise and follows the right-hand screw rule, the normal direction of each triangle can be calculated from the positions of the three vertices: ; In the formula, The normal vector of the triangle on the model that is currently being judged as the inner triangle face. , , are the coordinates of the three vertices of this triangle; S22, for each triangular face of the membrane structure, calculate whether the normal direction of the current triangular face intersects with any triangular face on the model; if there is a triangular face that intersects with the normal direction of the current triangular face, it is the inner side face, and the points on it are the inner surface vertices; otherwise, it is the outer side face, and the corresponding vertices are the outer surface vertices, and the remaining vertices are the inner vertices generated by tetrahedronization; S3. Add connections between membrane structures to simulate viscosity, specifically: S31. The specific method of constructing the connection between the two models is to connect the inner side vertices of the outer layer model vertically to the outer side triangles of the inner layer model, thereby generating a series of viscosity lines; S32, mass spring modeling, giving physical properties to the adhesion line; S33. After the modeling display is completed, it can be applied to the corresponding local anatomical simulation operation. The adhesion line between two adjacent layers of film-like tissue is visualized and the particle spring method is used to add viscosity.

2. The method for simulating viscosity between thin membrane tissues based on mass springs according to claim 1, characterized in that: The way to determine the intersection of normal and triangle is: S22.1, if satisfied , the normal is parallel to the triangle and does not intersect, where: , , are the three vertices of the triangle; In the formula, is the normal of any triangle on the model except the currently judged triangle, , , Respectively represent The components of the vector on the x-axis, y-axis, and z-axis, , , Respectively represent The components of the vector on the x-axis, y-axis, and z-axis, and the latter represent The component of the vector on the x-axis; S22.2, otherwise, there is an intersection , further determine the position of the intersection point. If the intersection point is inside the triangle, it is considered that the normal line and the triangle intersect. The method for determining if a point is inside the triangle is as follows: ,in, , , , respectively , , , area; The intersection point between the normal of the triangle to be judged as the inner triangle face and any other triangle. is any other triangle on the model except the one currently being judged as the inner side triangle; a, b, c are the three vertices of the triangle , , The intersection point is three triangles composed of three vertices of the triangle.

3. The method for simulating viscosity between thin membrane tissues based on mass springs according to claim 1, characterized in that: In the S31, the specific construction method is: S31.

1. For each vertex on the outer model , draw a perpendicular line to the triangle face of the inner model, and if the foot of the perpendicular line is inside the triangle, return the foot of the perpendicular line and get the triangle , vertical foot The calculation method is: ， ， ， Where n=norm((t2-t1)*(t3-t1)), , , are the coordinates of the triangle vertices on the inner model, are the vertex coordinates on the outer model; S31.2, select a perpendicular line with the shortest distance as the bonding line between the outer model vertex and the inner model; S31.

3. Since the end of the glue line can be located anywhere on the inner model triangle, the barycentric coordinates are used to mark the position of the end point on the triangle. The barycentric coordinates are calculated as follows: ,in, , , , respectively , , , area; The end point of the bonding line on the inner model. The vertices of the triangle on the inner model; The triangle is composed of point a, point b, and point p; The triangle is composed of point a, point c, and point p; The triangle is composed of point b, point c, and point p; It is a triangle formed by points a, b, and c.

4. The method for simulating viscosity between thin membrane tissues based on mass springs according to claim 1, characterized in that: In the S32, the specific modeling method is: S32.

1. According to Hooke's law, calculate the elastic force between mass point i and mass point j, that is, and vertical foot Elastic force on: ， ， in, is the elastic constant of the spring, is the existing length of the spring, Represents natural length; It is the endpoint of the bonding line on the outer model; is an endpoint of the glue line, that is, an endpoint on the outer model Elastic force on is the elastic force at the other end point P of the bonding line; S32.

2. Update the magnitude of the resultant force on the corresponding vertices on the model at both ends of the spring based on the elastic forces calculated at the two end points of the spring. The elastic forces at the perpendicular foot positions of the spring ends are transferred to the vertices of the triangle faces based on the coordinates of the center of gravity. Then, the velocities on the vertices are calculated and the positions of the vertices are updated.

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