JP2002099901A - Method and device for three-dimensional modeling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for three-dimensional modeling for providing a highly precise model without positional deflection on the surface and providing highly precise data in reuse and processing of the model (data) by CAD or CAE. SOLUTION: Among dimensions L1-Ln between outline both ends found from respective points on a characteristics curve 32 of brightness value in the outline both end parts of a cross sectional image of a test piece 31, made of the same material as a measured object, a brightness value br3 corresponding to a point on the characteristics curve 32, matching an actual dimension L3 between both ends of the test piece 31, is used as threshold for extraction of surface (outline) used in a triangular polygon generating process using a cross- sectional image of the measured object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for forming a three-dimensional model using a plurality of cross-sectional images of an object to be measured.

[0002]

2. Description of the Related Art A conventional method of this kind is disclosed in
There is one described in JP-A-328442. In other words, this means that each of two adjacent cross-sectional images in a plurality of cross-sectional images (planar images having contours) obtained at intervals along a certain direction of the measured object (three-dimensional object) is opposed to each other. Interpolation plane formation using a marching cube method for obtaining a hexahedron (cube) in which the luminance values (density) of four pixels are given to vertices and generating a triangular polygon based on a comparison result between the luminance value of each vertex and a threshold value A three-dimensional model is constructed by processing.

[0003] Here, the "marching cube method"
W. E. FIG. Lorensen and H.C. E. FIG. "Marching Cubes: A High Resolution 3D Surface Rec" by Cline
onstruction Algorithm "(1987; Computer Grap
hics 21 (4); pp. 163 to 169).

[0004]

However, in the above prior art, no consideration is given to the threshold value.
There were the following problems. That is, when a three-dimensional model is constructed from a plurality of cross-sectional images (tomographic images) such as X-ray CT images of the object to be measured, a threshold value is set for the luminance value of the cross-sectional image, and a comparison is made between the two. An interpolation plane forming process for obtaining the surface of the device under test is performed according to the result.

At this time, depending on the setting (value) of the threshold value, the surface position of the object to be measured is greatly deviated from the actual position. This is because the luminance value rises or falls (inclines) at the contour of the cross-sectional image even if the object is homogeneous.

[0006] Such a displacement of the surface position is hardly considered as a problem when it is desired to visually observe the surface state, for example, in a three-dimensional model for a living body diagnosis whose main purpose is to visually observe a lesion or a lesion. . However, when accuracy is required for the surface position of the object to be measured, such as when it is desired to measure the dimensions on the obtained three-dimensional model, the deviation of the surface position causes a decrease in accuracy, which is a serious problem. Become. This means that not only the outer surface (outer surface), but also the inner space structure, for example, the inner surface (inner surface) of the inner hole or cavity, that is, without questioning the inner and outer surfaces of the object to be measured, This can be said of the entire boundary surface with air, and improvement of this point has conventionally been demanded.

The present invention has been made in view of the above-mentioned demands, and provides a high-precision three-dimensional model in which the position of the surface (the entire boundary surface between the object to be measured and air) is not shifted.
It is an object to provide a dimensional modeling method and apparatus.

[0008]

In order to achieve the above object, an object of the present invention is to provide a method for measuring the distance between adjacent ones of a plurality of sectional images obtained at intervals along a certain direction of an object to be measured. A hexahedron in which the vertices are given the luminance values of the four pixels facing each other of the two cross-sectional images is obtained, and an interpolation plane forming process of generating a triangular polygon based on a comparison result between the luminance value of each vertex and a threshold value In the three-dimensional modeling method for constructing a three-dimensional model, the rise and fall characteristics of luminance values at both ends of a contour of a cross-sectional image of a test piece of the same material as the object to be measured and having known dimensions are used as the threshold. A brightness value corresponding to a point on the characteristic curve corresponding to an actual size between both ends of the test piece among dimensions between both ends of the contour obtained from each point on the curve is used.

According to a second aspect of the present invention, there is provided a sectional image capturing section for capturing a plurality of sectional images obtained at intervals along a certain direction of an object to be measured, and a threshold value is set. A threshold value setting unit and four opposed four cross-sectional images of two adjacent cross-sectional images in the plurality of cross-sectional images read from the cross-sectional image capturing unit;
A hexahedron in which the luminance values of the pixels are given to the vertices is obtained, and an interpolation plane forming process of generating a triangular polygon based on a comparison result between the luminance value of each vertex and the threshold value set in the threshold value setting unit is performed. In a three-dimensional modeling apparatus comprising a three-dimensional model forming unit for forming a three-dimensional model, the threshold value setting unit includes a contour of a cross-sectional image of a test piece having the same material and a known size as the object to be measured. Of the dimensions between both ends of the contour obtained from the points on the rising and falling characteristic curves of the luminance values at both end portions, the points corresponding to the points on the characteristic curve that match the actual dimensions between both ends of the test piece. A luminance value is set.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. Prior to that, first, the outline of the present invention will be described with reference to FIGS. The present invention is shown in FIG.
As shown in FIG. 1, a plurality of cross-sectional images CT1, CT2,... CTn obtained at regular intervals, usually at regular intervals, in the fixed direction of the DUT 11, in FIG.
The three-dimensional model 12 of the DUT 11 is formed by an interpolation plane forming process using −1 and CTn.

In constructing the three-dimensional model 12, as shown in FIG. 2, the plurality of cross-sectional images CT1,.
Four opposing pixels in two adjacent cross-sectional images CTn and CTn-1 in CTn, and four pixels p1 in the cross-sectional image CTn in the figure.
1 to p14 and four pixels p21 to p2 of the cross-sectional image CTn-1
A hexahedron in which the vertices ap1 to ap4, ap5 to ap8 are given the luminance value of 4 is obtained. Then, each vertex ap1 to ap8
The DUT 11 is formed by an interpolation surface forming process for generating a triangular polygon based on a result of comparison between the luminance value of the object and the threshold value.
(Combined surface of triangular polygons) 12 is constructed.

At this time, in the present invention, as shown in FIG. 3, the brightness at both ends of the contour of the cross-sectional image of the test piece 31 of the same material and the known size as the object to be measured 11 is used as the threshold value. Value rising and falling characteristic curve 32
Dimensions L1 to L between both ends of the contour obtained from the above points
n, the actual dimension L3 between both ends of the test piece 31
Brightness value b corresponding to a point on the characteristic curve 32 that matches
It is characterized by using r3. The hexahedron in this specification refers to a cube or a rectangular parallelepiped, and FIG. 2 illustrates the cube 21 as an example.

Next, an embodiment of the present invention will be described. FIG. 4 is a block diagram showing an embodiment of a three-dimensional modeling apparatus according to the present invention together with a CT apparatus for obtaining a plurality of CT images to be modeled, here, an X-ray CT apparatus. In this figure, 41 is an X-ray CT apparatus, and 42 is a three-dimensional modeling apparatus. The X-ray CT apparatus 41 includes a scanner unit 41a, a processing unit 41b, an operation unit 41c, and a monitor unit 41.
, CTn-1 and CTn (see FIG. 1) are obtained as described below.

That is, the scanner section 41a scans the DUT 11 while feeding it in a fixed direction, here the direction of arrow A, and collects a large number of scan data of planes parallel to each other at fixed intervals. The processing unit 41b generates cross-sectional images each having a CT value as a pixel value from the scan data. The generated cross-sectional image is displayed on the monitor unit 41c as a set of pixels having a luminance value corresponding to the pixel value, that is, a grayscale image, or stored in a storage device (not shown) inside or outside the X-ray CT apparatus 41. Is stored.

The three-dimensional modeling device 42 includes a cross-sectional image capturing unit 42a, a threshold setting unit 42b, a three-dimensional model forming unit 42c, a model storing unit 42d, and a monitor unit 42e.

Among these, the cross-sectional image capturing section 42a is used to store the multiplicity of cross-sectional images (data) obtained by the X-ray CT apparatus 41.
CTn are fetched from the processing unit 41b or the storage device. The threshold value setting unit 42b sets a threshold value used for an interpolation plane forming process described later. 3D model construction unit 4
2c constitutes a three-dimensional model of the DUT 11 by using the above-described cross-sectional images CT1,.

The model storage section 42d comprises a storage device,
The three-dimensional model (data) obtained by the three-dimensional model forming unit 42c is stored. The monitor unit 42e displays the three-dimensional model obtained by the three-dimensional model forming unit 42c.

Here, the three-dimensional model forming unit 42c
When constructing a three-dimensional model, as shown in FIG. 5, two adjacent cross-sectional images in the multiple cross-sectional images CT1,... CTn, for example, each of the opposed cross-sectional images CTn, CTn-1 4 pixels (total 8 pixels) p11 to p14, p21
As shown in FIG. 6, the vertex values ap1 to ap
The rectangular parallelepiped 61 given to 8 is obtained.

Here, the rectangular parallelepiped 61 is further divided into six tetrahedrons 61a to 61f (see FIGS. 7A to 7F), and the luminance value and the threshold value of each vertex ap of each of the tetrahedrons 61a to 61f are determined. Based on the result of comparison with the above, an interpolation plane forming process applying the aforementioned marching cube method for generating a triangular polygon is performed.

More specifically, a triangular polygon is generated as follows by comparing the luminance value of each vertex ap of each of the tetrahedrons 61a to 61f with a threshold value. Now, the brightness values of the vertices ap1, ap5, ap7, and ap8 of the tetrahedron 61a are allocated to a case where the brightness value is smaller than a threshold value (how to obtain it), equal to the threshold value, or larger than the threshold value. It is assumed that the result shown in FIG. 8 is obtained as a result of the addition.

Here, each vertex ap1, ap5, ap
Fifteen types 1 to 15 are set as “cases” for distributing the brightness values of 7, ap8 based on the result of comparison with the threshold value. In the figure, the notation of "small" is smaller than the threshold value (air),
The notation “equal” refers to the case where it is equal to the threshold, and the notation “large” refers to the case where it is larger than the threshold (the DUT 11).
Numerical values shown in the columns of “small”, “equal”, and “large” are sorted and added to the comparison results of the brightness values of the vertices ap1, ap5, ap7, and ap8 with the threshold values in the above cases. The results are shown. The column of “surface to be generated” indicates the presence or absence and the number of triangular polygons generated in each of Cases 1 to 15.

The case where the surface of the DUT 11 (the boundary surface between the DUT 11 and the air) is generated is the case where “small” (air) and “large” (the DUT 11) are simultaneously included. In the illustrated example, cases 7 to 12 correspond to the case setting, and triangular polygons are generated for the cases 7 to 12. Case 13 is "small" (air) and "large"
(Measurement object 11) is not included at the same time, but here, the setting is such that a triangular polygon is generated. Case 7
Examples of the forms of the triangular polygons generated in Steps (a) to (13) are as shown in 91a to 91g in FIGS. 9 (a) to 9 (g). 9 (a) to 9 (g),
7A indicate the same parts.

The above processing is performed for the target pixel (p11 in FIG. 5).
) For all pixels by shifting
A three-dimensional model (composite surface of triangular polygons) 12 of the DUT 11 is formed by shifting the paired cross-sectional images one by one for all cross-sectional images.

At this time, a luminance value obtained by the following method is used as the threshold value. To be described with reference to FIG. 3, first, when the DUT 11 is an aluminum structure, the DUT 11 is referred to as an aluminum material.
A cross-sectional image of the test piece 31 of the same material and having a known size by the X-ray CT apparatus 41 is prepared. next,
Dimensions L1 to Ln between both ends of the contour obtained from each point on the rising and falling characteristic curves (slope) 32 at the both ends of the contour of the cross-sectional image of the test piece 31
And the actual dimension L3 between both ends of the test piece 31 are compared. Then, the characteristic curve (slope) 3 where they match.
A luminance value br3 corresponding to the point above the second point is obtained, and this is used as the threshold value. The acquisition of such a brightness value br3 is performed by an operation of a CPU (not shown) in the three-dimensional model forming unit 42c. This luminance value (threshold) b
r3 is stored and set in advance in the threshold value setting unit 42b.

Next, a modeling procedure by the three-dimensional modeling device 42 will be described with reference to FIG. First, the cross-sectional image capturing unit 42a captures the multiple cross-sectional images (data) CT1,..., CTn of the DUT 11 from the X-ray CT apparatus 41 or an external storage device (not shown) (step 1001). The cross-sectional images CT1,..., CTn from the X-ray CT apparatus 41 or the storage device to the cross-sectional image capturing unit 42a are captured via a storage medium such as a floppy (registered trademark) disk or a communication network.

Subsequently, a threshold value (luminance value) br3 is set in the threshold value setting section 42b (step 1002).
This step 1002 and the above-mentioned step 1001 may be reversed.

In step 1003, the three-dimensional model forming section 42c sets the above-mentioned cross-sectional images CT1,.
And a three-dimensional model (composite surface of triangular polygons) of the DUT 11 is formed by an interpolation surface forming process using the marching cube method. The interpolation plane forming process is performed using the threshold value (brightness value) br3 set in the threshold value setting unit 42b in step 1002 as the threshold value.

The constructed three-dimensional model (data) is represented by S
The data is stored in the model storage unit 42d in a general-purpose format such as TL, IGES, and STEP, and is displayed on the monitor unit 42e.

In the above embodiment, the case where the threshold value br3 is obtained based on the outer diameter of the cylindrical test piece 31 has been described. However, the present invention is not limited to this. For example, the threshold value may be obtained based on the size of one side of the end face of the prismatic test piece. Alternatively, the threshold value may be obtained based on the dimensions of the device under test.

[0030]

As described above, according to the present invention, the threshold value for extracting the surface (contour) used in the process of generating a triangular polygon using the cross-sectional image of the measured object, In the characteristic curve that matches the actual dimension between both ends of the test piece, of the dimensions between the both ends of the contour obtained from each point on the characteristic curve of the rise and fall of the luminance value at both ends of the contour of the cross-sectional image of the test piece of the same material Since the brightness value corresponding to the point is used, that is, a surface is created between pixels of the cross-sectional image according to the actual dimensions, the position of the entire surface (the entire boundary surface between the object to be measured and air) is located. There is an effect that a high-precision three-dimensional model without deviation can be obtained. In particular, the absence of displacement on the entire boundary surface between the object to be measured and the air means that the dimensional accuracy based on the inner surface position of the internal space structure is high. Therefore, the dimensions of the internal space structure can be measured with high accuracy without actually cutting the object to be measured, and the cutting may cause the object to be deformed or the object to be measured to be unusable after measurement. There is also an effect that can be avoided.

According to the present invention, since the accuracy of the obtained three-dimensional model (data) is high, the data obtained by reusing or processing the model by CAD, CAM, CAE or the like also has high accuracy. There is also a positive effect. Also,
Obtaining a three-dimensional model of an object without CAD data also has the effect of enabling highly reliable analysis by CAE using the model. Furthermore, since the surface generated according to the present invention is basically a set (mesh) of triangular polygons, a secondary effect that can be handled relatively easily in CAE, which similarly performs analysis based on a triangular mesh. There is also.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram of three-dimensional modeling of an object to be measured.

FIG. 2 is a schematic explanatory diagram of a process of generating a triangular polygon used in the present invention.

FIG. 3 is an explanatory diagram of a method of acquiring a luminance value used as a threshold value in the above processing.

FIG. 4 is a block diagram showing an embodiment of a three-dimensional modeling device according to the present invention together with an X-ray CT device.

FIG. 5 is an explanatory diagram of a cross-sectional image pair and a pixel set used in generating a minimum unit of a triangular polygon in a process of generating a triangular polygon in the embodiment.

FIG. 6 is an explanatory diagram of a rectangular parallelepiped for generating a triangular polygon from each luminance value of the pixel set shown in FIG. 5;

FIG. 7 is an explanatory diagram of six tetrahedrons obtained by further dividing the rectangular parallelepiped shown in FIG. 6;

FIG. 8 compares the luminance value at each vertex of each tetrahedron shown in FIG. 7 with a threshold value used in a process of generating a triangular polygon, and determines the result and the presence / absence and number of corresponding triangular polygons for each case. FIG.

FIG. 9 is a diagram exemplifying a form of a triangular polygon when it is determined that a triangular polygon is generated in FIG. 8;

FIG. 10 is a flowchart illustrating a modeling procedure by the three-dimensional modeling device of the present invention shown in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 DUT 12 Dimensional model 21 Cube (Hexahedron) 31 Test piece 32 Rise and fall characteristic curve of a brightness value CT1 ... CTn Cross-sectional image L1-Ln Dimension between both ends of contour of cross-sectional image of test piece L3 Both ends of test piece Actual dimension br3 Brightness value (threshold) 42 3D modeling device 42a Cross-sectional image capturing unit 42b Threshold setting unit 42c 3D model configuration unit 42d Model storage unit 42e Monitor unit

Continued on the front page F term (reference) 4C093 CA50 FC12 FF16 FF22 FF35 FF42 FF50 5B057 DA11 DA20 DC16 DC22 5B080 AA14

Claims (2)

[Claims] 1. A hexahedron in which the vertices are provided with the luminance values of four opposing pixels of two adjacent cross-sectional images in a plurality of cross-sectional images obtained at intervals along a certain direction of an object to be measured. Is obtained, and an interpolation plane forming process of generating a triangular polygon based on the comparison result between the luminance value of each vertex and the threshold value is performed.
In the three-dimensional modeling method for constructing a three-dimensional model, as the threshold value, a rising and falling characteristic curve of a luminance value at both ends of a contour of a cross-sectional image of a test piece having the same material as the object to be measured and having a known dimension. A three-dimensional model characterized by using a luminance value corresponding to a point on the characteristic curve which coincides with an actual dimension between both ends of the test piece among dimensions between both ends of the contour obtained from each of the above points. Method. 2. A cross-sectional image capturing unit that captures a plurality of cross-sectional images obtained at intervals along a certain direction of an object to be measured, a threshold setting unit that sets a threshold, and the cross-sectional image Adjacent 2 in a plurality of cross-sectional images read from the capturing unit
A hexahedron is obtained in which the vertices are given the luminance values of the four pixels facing each other of the cross-sectional images of the sheet, and a triangle is set based on the comparison result between the luminance value of each vertex and the threshold value set in the threshold value setting unit A three-dimensional model forming unit configured to form a three-dimensional model by an interpolation surface forming process for generating polygons, wherein the threshold value setting unit has a dimension of the same material as the object to be measured. The rising and falling of the luminance values at both ends of the contour of the cross-sectional image of the known test piece coincides with the actual dimension between both ends of the test piece among the dimensions between both ends of the contour obtained from each point on the falling characteristic curve. A three-dimensional modeling device, wherein a luminance value corresponding to a point on the characteristic curve is set.