Three-dimensional model inner cavity appearance joint feature coding calculation method and system

Abstract

The invention provides an inner cavity appearance joint feature coding calculation method and system of a three-dimensional model, and belongs to the technical field of computer aided design. Comprising the following steps: S1, voxelization of a three-dimensional model: converting the three-dimensional model of a part into an original voxel model; s2, carrying out posture uniformization treatment on the parts; s3, the inner cavity of the original voxel model is filled, the interior of the original voxel model is completely filled, a voxel model without a recess is obtained, Boolean difference operation is conducted on the voxel model with the filled inner cavity and the original voxel model of the part, and an inner cavity model of the part is obtained; taking the voxel model with the filled inner cavity as a shape entity; s4, analyzing an inner cavity connected domain, and dividing the obtained inner cavity model into a plurality of inner cavity entities; s5, shape feature calculation; and S6, combining structural feature codes, and combining the shape features of the shape entity and the shape features of the plurality of inner cavity entities to form the overall features of the three-dimensional part.

Description

Technical Field

[0001] The invention relates to the technical field of computer-aided design, and in particular to a method for calculating the combined feature coding of an inner cavity shape of a three-dimensional model. Background Art

[0002] With the widespread application of computer-aided design (CAD) in the manufacturing industry, CAD three-dimensional models have become one of the basic data forms in modern manufacturing production, and with the continuous progress of production and manufacturing, the number of CAD part models has gradually increased. At present, the developed CAD part database Trace-Parts alone has included more than 100 million mechanical parts. Quickly and accurately retrieving part models is of great significance for the design of new parts and the manufacturing process design of new parts.

[0003] However, the current retrieval method of part 3D models often relies on keyword descriptions. The target parts are retrieved through text descriptions, which is effective for the function, type and other features of the parts, but the structural characteristics of the parts are often difficult to describe and retrieve through text descriptions, and the part structure is an important factor in realizing the function of the part and affecting the part manufacturing process. Therefore, it is of great significance to retrieve part models with similar structures by inputting the part model (similar to image search, content-based retrieval) for fast and accurate retrieval of target parts, and the key to realizing this retrieval method lies in how to represent the structural features of the parts, that is, how to encode the 3D model structure.

[0004] At present, the main methods for characterizing the structure of three-dimensional models include statistical shape features, topological structure diagrams, projection diagrams, function transformations, and encoding methods based on deep learning, etc. These retrieval methods often regard the shape of the three-dimensional model as a whole. However, the inner cavity of mechanical parts also plays an important role in the functionality and processing of mechanical parts, and is an important part of the part structure. Therefore, a joint feature encoding calculation method for the inner cavity and shape of a three-dimensional model is provided to accurately express the reasonable structural features of the three-dimensional model with an inner cavity, which is conducive to the rapid and accurate recognition of the three-dimensional model. Summary of the invention

[0005] In view of this, the present invention proposes a method and system for calculating the combined feature coding of the inner cavity and outer shape of a three-dimensional model that not only considers the external features of the part, but also fully considers the inner cavity structure and distribution conditions to more effectively represent the overall structural characteristics of the part.

[0006] In one aspect, the present invention provides a method for calculating the inner cavity shape joint feature coding of a three-dimensional model, comprising the following steps:

[0007] S1: 3D model voxelization, converting the 3D model of the part into a primitive voxel model;

[0008] S2: The posture of the parts is unified to remove the influence of the placement of the original voxel model on the structural features;

[0009] S3: Filling the inner cavity of the original voxel model, completely filling the inner cavity of the original voxel model to obtain a voxel model without depressions, performing a Boolean difference operation between the voxel model after the inner cavity is filled and the original voxel model of the part to obtain the inner cavity model of the part; the voxel model after the inner cavity is filled is used as the outer shape entity;

[0010] S4: analysis of the inner cavity connected domain, dividing the obtained inner cavity model into several inner cavity entities;

[0011] S5: shape feature calculation;

[0012] S6: Combined structural feature coding, combining the shape features of the outer shape entity and the shape features of several inner cavity entities to form the overall features of the three-dimensional part.

[0013] On the basis of the above technical solution, preferably, the content of step S1 is: construct the world coordinate system and X, Y and Z axes where the part is located; in the three-dimensional space, the voxel model is represented by the following equation: t = f(x, y, z), where f(·) represents the continuous distribution in space; (x, y, z) is the coordinate in the world coordinate system, corresponding to the point on the three-dimensional model of the part; t represents the mass of the voxel, and t = 0 indicates that the voxel is empty.

[0014] Preferably, the content of step S2 is: using the second-order center distance matrix C to represent the original voxel model, assuming that the voxel is a cube with uniform internal mass distribution and a side length of l, v = V i +[xyz] T , V i is the voxel of the three-dimensional model of the part; v represents the voxel V i The corresponding point on the 3D model of the part; x, y, z∈[-l / 2, l / 2]; the centroid of the original voxel model N is the number of voxels in the original voxel model.

[0015] Further preferably, the content of step S3 is: traverse each voxel in the X-axis, Y-axis and Z-axis directions of the world coordinate system respectively, and calculate the maximum depth and minimum depth of each voxel position of the part in each YZ plane, XZ plane and XY plane; after traversing the three axial directions and three planes, completely fill the internal space of the original voxel model in the X, Y and Z directions to obtain a voxel model after the inner cavity is completely filled; perform a Boolean difference operation on the voxel model after the inner cavity is completely filled with the original voxel model, subtract the part corresponding to the original voxel model from the voxel model after the inner cavity is completely filled, and the remaining voxel model part is the inner cavity model of the part formed by filling the inner cavity, and the inner cavity model is a whole.

[0016] More preferably, the specific content of step S4 is: marking the interconnected voxels in the inner cavity model with the same label, marking the non-connected voxels with different labels, and dividing the inner cavity model into several non-connected inner cavity entities by setting different labels; the original voxel model of the part is represented as a Boolean operation result of an outer shape entity without depressions and several inner cavity entities.

[0017] Further preferably, to determine whether the voxels in the inner cavity model are interconnected, a local coordinate system is established with the current voxel to be marked as a reference, and the origin of the local coordinate system coincides with the center of mass of the voxel to be marked; the x-axis of the local coordinate system is defined as the center of mass of the voxel to be marked from left to right horizontally through the center of mass; the y-axis of the local coordinate system is defined as the center of mass of the voxel to be marked from back to front horizontally, and the z-axis of the local coordinate system is defined as the center of mass of the voxel to be marked from bottom to top vertically; for the current voxel to be marked, if the labels of the voxels adjacent to the negative semi-axis of the x-axis of the local coordinate system, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis are all empty voxels, then the current voxel to be marked is assigned as Empty voxel, and connected with adjacent empty voxels; if the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are not completely empty voxels, then the empty voxel with the smallest label among the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, or the positive semi-axis of the z-axis is assigned to the label of the current voxel to be marked; if the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are different and are not empty voxels, it means that the current voxel to be marked has no empty voxels connected to it, and a new label is assigned to the current voxel to be marked.

[0018] Further preferably, the specific content of step S5 is: calculate the shape features of the obtained outer shape entity and several inner cavity entities respectively, calculate the shape features of the outer shape entity obtained in step S3 and the several inner cavity entities obtained in step S4 respectively, and calculate the percentage position and volume of the center of mass of the outer shape entity and the inner cavity entity in the three-dimensional model; obtain the structural feature coding corresponding to the shape features, the percentage position and volume of the center of mass in the three-dimensional model.

[0019] More preferably, the specific content of step S6 is: combining the structural feature codes corresponding to the outer shape entity and the inner cavity entity, and arranging the combined structural feature codes in sequence according to the order of outer shape entity first, then inner cavity entity, and the distance from the center of mass of the three-dimensional model from large to small.

[0020] More preferably, the shape characteristics of the outer shape entity and the plurality of inner cavity entities are expressed using D2 coding.

[0021] On the other hand, the present invention also provides a system for calculating the joint feature coding of the inner cavity shape of a three-dimensional model, including a processor and a storage medium, wherein the storage medium stores the above-mentioned method for calculating the joint feature coding of the inner cavity shape of the three-dimensional model, and the processor is used to execute the method stored in the storage medium.

[0022] The present invention provides a method and system for calculating the inner cavity shape combined with feature coding of a three-dimensional model, which has the following beneficial effects compared with the prior art:

[0023] (1) The present invention does not simply regard the internal space of the three-dimensional part or all the cavity areas as a whole, but performs axial filling and Boolean operations on the internal area of ​​the three-dimensional part according to the voxel model to obtain the filled voxel model and the voxel model of the cavity part, respectively obtain shape features, and recombine them into a unified form of structural feature coding;

[0024] (2) The shape features of the outer shape entity and several inner cavity entities are expressed using D2 coding. By taking two different points on the surface of the entity at random and repeatedly obtaining the distance distribution of the two points, the shape features of the outer shape entity and the cavity entity are expressed, which is conducive to reading and storing the content of the structural features in a coded form. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1A schematic diagram of a three-dimensional model filling and cavity of a part according to a method and system for calculating the inner cavity shape of a three-dimensional model combined with feature coding of the present invention;

[0027] Figure 2 The local coordinate system of the voxels to be marked in the method and system for calculating the inner cavity shape of a three-dimensional model of the present invention;

[0028] Figure 3 It is a schematic diagram of a flow chart of a method for calculating a combined feature coding of an inner cavity shape of a three-dimensional model and a system for coding structural features of the system according to the present invention;

[0029] Figure 4 A schematic diagram of the structure of the structural feature coding of a method and system for calculating the combined feature coding of the inner cavity shape of a three-dimensional model of the present invention;

[0030] Figure 5 It is a schematic diagram of an embodiment of a method and system for calculating the inner cavity shape combined with feature coding of a three-dimensional model of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0032] like Figure 1 As shown, on the one hand, the present invention provides a method for calculating the inner cavity shape joint feature coding of a three-dimensional model, comprising the following steps:

[0033] S1: 3D model voxelization, converting the 3D model of the part into a primitive voxel model.

[0034] The content of step S1 is: construct the world coordinate system and X, Y and Z axes of the part; in three-dimensional space, the voxel model is represented by the following equation: t = f(x, y, z), where f(·) represents the continuous distribution in space; (x, y, z) is the coordinate in the world coordinate system, corresponding to the point on the three-dimensional model of the part; t represents the mass of the voxel, and t = 0 indicates that the voxel is empty.

[0035] S2: The posture of the parts is unified to remove the influence of the placement of the original voxel model on the structural features.

[0036] Assuming that the mass is uniformly distributed in the three-dimensional model, some parameters are only related to the geometric shape of the model and usually remain unchanged when the model is transformed. The eigenvalue of the second-order central moment does not change during the rotation of the model and can be used to show the characteristics of the model. Therefore, the present invention uses the second-order center distance to represent the original voxel model.

[0037] The second-order center distance matrix C is used to represent the original voxel model, and the voxel is a cube with uniform internal mass distribution and side length l, v = V i +[xyz] T , V i is the voxel of the three-dimensional model of the part; v represents the voxel V i The corresponding point on the 3D model of the part; x, y, z∈[-l / 2, l / 2]; the centroid of the original voxel model N is the number of voxels in the original voxel model, then

[0038] S3: Filling the inner cavity of the original voxel model, completely filling the interior of the original voxel model to obtain a voxel model without depressions, performing a Boolean difference operation between the voxel model after the inner cavity is filled and the original voxel model of the part to obtain the inner cavity model of the part; and taking the voxel model after the inner cavity is filled as the outer shape entity.

[0039] The specific contents are as follows: traverse each voxel in the X-axis, Y-axis and Z-axis directions of the world coordinate system respectively, and calculate the maximum depth and minimum depth of each voxel position of the part in each YZ plane, XZ plane and XY plane; after traversing the three axial directions and three planes, completely fill the internal space of the original voxel model in the X, Y and Z directions to obtain a voxel model with the inner cavity completely filled; perform a Boolean difference operation on the voxel model with the inner cavity completely filled and the original voxel model, subtract the part corresponding to the original voxel model from the voxel model with the inner cavity completely filled, and the remaining voxel model part is the inner cavity model of the part formed by filling the inner cavity, and the inner cavity model is a whole.

[0040] The process of this step is illustrated as follows: there is a point on the XY plane, which corresponds to the projection of multiple points at different distances from the XY plane in the Z-axis direction. The entities corresponding to the movement along the positive direction of the Z-axis and the negative direction of the Z-axis are the boundaries of the inner cavity at the corresponding positions, and are also the characteristic points between the maximum depth and the minimum depth of the inner cavity.

[0041] S4: Analysis of the connected domain of the inner cavity, dividing the obtained inner cavity model into several inner cavity entities.

[0042] The rules of connected domain analysis are as follows: when a voxel is within its 6-neighborhood, i.e., the six adjacent positions above, below, front, back, left, and right of the voxel, determine whether there is another voxel. If so, the two voxels are considered connected. Two different voxels connected to the same voxel are also connected. When a voxel is not adjacent to any connected body of another voxel, the two voxels are not connected to each other.

[0043] The specific contents are as follows: the interconnected voxels in the inner cavity model are marked with the same label, and the non-connected voxels are marked with different labels. The inner cavity model is divided into several non-connected inner cavity entities by setting different labels; the original voxel model of the part is represented as a Boolean operation result of an outer shape entity without concave shapes and several inner cavity entities.

[0044] Reference Figure 2 To determine whether the voxels in the inner cavity model are interconnected, the local coordinate system is established based on the current voxel to be marked as the reference, and the origin of the local coordinate system coincides with the centroid of the voxel to be marked; the x-axis of the local coordinate system is defined as passing through the centroid of the voxel to be marked horizontally from left to right; the y-axis of the local coordinate system is defined as passing through the centroid of the voxel to be marked horizontally from back to front, and the z-axis of the local coordinate system is defined as passing through the centroid of the voxel to be marked vertically from bottom to top:

[0045] For the voxel to be labeled, if the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are all empty voxels, then the voxel to be labeled is assigned as an empty voxel, and is connected to the adjacent empty voxels.

[0046] If the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are not all empty voxels, then the empty voxel with the smallest label among the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, or the positive semi-axis of the z-axis is assigned to the label of the current voxel to be labeled;

[0047] If the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are different and are not empty voxels, it means that the current voxel to be labeled has no empty voxels connected to it, and a new label is assigned to the current voxel to be labeled.

[0048] S5: Shape feature calculation.

[0049] The specific contents are as follows: shape features are calculated for the obtained outer shape entity and several inner cavity entities respectively, shape features of the outer shape entity obtained in step S3 and several inner cavity entities obtained in step S4 are calculated respectively, and the percentage position and volume of the center of mass of the outer shape entity and the inner cavity entity in the three-dimensional model are calculated; structural feature codes corresponding to shape features, percentage position and volume of the center of mass in the three-dimensional model are obtained.

[0050] like Figure 3 As shown, in one embodiment, the shape characteristics of the outer shape entity and the plurality of inner cavity entities are expressed using D2 coding.

[0051] S6: Combined structural feature coding, combining the shape features of the outer shape entity and the shape features of several inner cavity entities to form the overall features of the three-dimensional part.

[0052] The specific content is: combine the structural feature codes corresponding to the outer shape entity and the inner cavity entity, and arrange the combined structural feature codes in order of the outer shape entity first and the inner cavity entity second, and the distance from the centroid of the three-dimensional model from large to small.

[0053] On the other hand, the present invention also provides a system for calculating the joint feature coding of the inner cavity shape of a three-dimensional model, including a processor and a storage medium, wherein the storage medium stores the above-mentioned method for calculating the joint feature coding of the inner cavity shape of the three-dimensional model, and the processor is used to execute the method stored in the storage medium.

[0054] The following is an embodiment of the present invention, which is used to illustrate the method of sampling and joint feature coding to describe the inner cavity structure.

[0055] S101: Input the 3D model of the casting, such as Figure 5 As shown in (a), it can be seen that the length direction is the X-axis direction, the height direction is the Z-axis direction, and the thickness direction is the Y-axis direction.

[0056] S102: Perform posture consistency processing on the input three-dimensional model of the casting, calibrate it to the standard posture, and adjust the orientation of the casting through posture transformation. Figure 5 From the orientation (b), it can be seen that the X-axis direction of the casting is the longest, the Y-axis direction is the second longest, and the Z-axis direction is the shortest. After the posture is adjusted, the length direction of the casting is the X-axis direction, the height direction is the Y-axis direction, and the thickness direction is the Z-axis direction.

[0057] S103: voxelize the three-dimensional model of the casting, such as Figure 5 as shown in (c).

[0058] S104: Fill the inner cavity of the casting. Figure 5As shown in (d), the yellow part is the voxel after the inner cavity is filled, which together with the time-lapse 3D model constitutes a complete external contour. Based on this filled voxel structure, characteristic parameters such as the D2 feature vector and the centroid position are calculated for the external contour of the voxel result.

[0059] S105: Extract the voxels corresponding to the inner cavity from the complete voxel structure, such as Figure 5 As shown in (e).

[0060] S106: Segment the independent voxels through connected domain analysis and use different colors to mark them. Figure 5 As shown in (f).

[0061] S107: Sequentially number each inner cavity entity in the ascending order of the projection coordinates of each independent inner cavity entity on the X-axis, and combine them in the order of appearance feature code-first inner cavity feature code-second inner cavity feature code-... to obtain a combined structural feature code.

[0062] D2 encoding is usually a 64-bit array, but the length can also be customized. It usually uses a line graph to describe the array formed by the size of the feature points in two dimensions.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calculating the inner cavity shape joint feature coding of a three-dimensional model, characterized in that: The steps include: S1: 3D model voxelization, converting the 3D model of the part into a primitive voxel model; S2: The posture of the parts is unified to remove the influence of the placement of the original voxel model on the structural features; S3: Filling the inner cavity of the original voxel model, completely filling the inner cavity of the original voxel model to obtain a voxel model without depressions, performing a Boolean difference operation between the voxel model after the inner cavity is filled and the original voxel model of the part to obtain the inner cavity model of the part; the voxel model after the inner cavity is filled is used as the outer shape entity; S4: analysis of the inner cavity connected domain, dividing the obtained inner cavity model into several inner cavity entities; S5: shape feature calculation; S6: Combined structural feature coding, combining the shape features of the outer shape entity and the shape features of several inner cavity entities to form the overall features of the three-dimensional part.

2. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 1, characterized in that: The content of step S1 is: construct the world coordinate system and X, Y and Z axes of the part; in three-dimensional space, the voxel model is represented by the following equation: t = f(x, y, z), where f(·) represents the continuous distribution in space; (x, y, z) is the coordinate in the world coordinate system, corresponding to the point on the three-dimensional model of the part; t represents the mass of the voxel, and t = 0 indicates that the voxel is empty.

3. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 2 is characterized in that: Step S2 includes: using the second-order center distance matrix C to represent the original voxel model, assuming that the voxel is a cube with uniform internal mass distribution and a side length of l, v = V i +[xyz] T , V i is the voxel of the three-dimensional model of the part; v represents the voxel V i The corresponding point on the 3D model of the part; x, y, z∈[-l / 2, l / 2]; the centroid of the original voxel model N is the number of voxels in the original voxel model.

4. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 3 is characterized in that: The content of step S3 is: traverse each voxel in the X-axis, Y-axis and Z-axis directions of the world coordinate system respectively, and calculate the maximum depth and minimum depth of each voxel position of the part in each YZ plane, XZ plane and XY plane; after traversing the three axial directions and three planes, completely fill the internal space of the original voxel model in the X, Y and Z directions to obtain a voxel model with the inner cavity completely filled; perform a Boolean difference operation on the voxel model with the inner cavity completely filled and the original voxel model, subtract the part corresponding to the original voxel model from the voxel model with the inner cavity completely filled, and the remaining voxel model part is the inner cavity model of the part formed by filling the inner cavity, and the inner cavity model is a whole.

5. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 4, characterized in that: The specific content of step S4 is: mark the interconnected voxels in the inner cavity model with the same label, mark the non-connected voxels with different labels, and divide the inner cavity model into several non-connected inner cavity entities by setting different labels; the original voxel model of the part is represented as a Boolean operation result of an outer shape entity without concave shapes and several inner cavity entities.

6. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 5, characterized in that: To determine whether the voxels in the inner cavity model are interconnected, the local coordinate system is established with the current voxel to be marked as the reference, and the origin of the local coordinate system coincides with the mass center of the voxel to be marked; the x-axis of the local coordinate system is defined as passing through the mass center of the voxel to be marked horizontally from left to right; the y-axis of the local coordinate system is defined as passing through the mass center of the voxel to be marked horizontally from back to front, and the z-axis of the local coordinate system is defined as passing through the mass center of the voxel to be marked vertically from bottom to top; For the voxel to be marked currently, if the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are all empty voxels, then the voxel to be marked currently is assigned as an empty voxel, and is connected with the adjacent empty voxels; if the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are not completely empty voxels, then the empty voxel with the smallest label among the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, or the positive semi-axis of the z-axis is assigned to the label of the voxel to be marked currently; if the labels of the voxels adjacent to the negative semi-axis of the x-axis, the negative semi-axis of the y-axis, and the positive semi-axis of the z-axis in the local coordinate system are different and are not empty voxels, it means that the voxel to be marked currently has no empty voxels connected to it, and a new label is assigned to the voxel to be marked currently.

7. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 5, characterized in that: The specific content of step S5 is: calculate the shape features of the obtained outer shape entity and several inner cavity entities respectively, calculate the shape features of the outer shape entity obtained in step S3 and several inner cavity entities obtained in step S4 respectively, and calculate the percentage position and volume of the center of mass of the outer shape entity and the inner cavity entity in the three-dimensional model; obtain the structural feature coding corresponding to the shape features, the percentage position and volume of the center of mass in the three-dimensional model.

8. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 7, characterized in that: The specific content of step S6 is: combining the structural feature codes corresponding to the outer shape entity and the inner cavity entity, and arranging the combined structural feature codes in order of the outer shape entity first and the inner cavity entity second, and the distance from the centroid of the three-dimensional model from large to small.

9. The method for calculating the inner cavity shape joint feature coding of a three-dimensional model according to claim 7, characterized in that: The shape features of the outer shape entity and the plurality of inner cavity entities are expressed using D2 coding.

10. A system for calculating the joint feature coding of the inner cavity shape of a three-dimensional model, comprising a processor and a storage medium, wherein the storage medium stores the method for calculating the joint feature coding of the inner cavity shape of a three-dimensional model as described in any one of claims 1 to 9, and the processor is used to execute the method stored in the storage medium.

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