A 3D projection method for dynamic sand table

Abstract

This invention relates to a three-dimensional projection method for a dynamic sand table, belonging to the field of projection technology. The method includes: establishing an image space coordinate system and an object space coordinate system; determining at least three pairs of non-coplanar and collinear position points on the image plane and the three-dimensional terrain bottom surface to determine the coordinates of the projection center in the object space coordinate system; determining the offset between the perpendicular point from the projection center to the image plane and the center of the image plane based on the coordinates of the projection center in the object space coordinate system, the size of the image, and the size of the three-dimensional terrain bottom surface; correcting the image using the offset to obtain a projected image; establishing the geometric relationship between the orthophoto image and the corrected image based on the principle of triangle similarity; obtaining the position of the correction point based on the position of the orthophoto point and the geometric relationship; assigning the grayscale value of the orthophoto point to the corresponding correction point; all the correction points after assignment forming the corrected image; and performing three-dimensional projection using the corrected image. This invention achieves distortion-free and undistorted three-dimensional projection.

Description

Technical Field

[0001] This invention relates to a three-dimensional projection method for a dynamic sand table, belonging to the field of projection technology. Background Technology

[0002] Currently, three-dimensional terrain representation is achieved through two main methods: virtual representation in computers and physical representation, such as traditional handmade sand tables and 3D-printed sand tables. While computer-generated virtual representation is convenient and quick, it lacks realism and is not suitable for observation by multiple people from multiple angles. Traditional handmade sand tables require high skill levels and have poor precision. 3D-printed sand tables are for single use only; reprinting is required for different areas. Dynamic sand table technology can effectively address these issues. To achieve dynamic three-dimensional terrain representation, such as… Figure 1 As shown, based on the three-dimensional terrain 3, the image of the photograph 2 is projected onto the three-dimensional terrain 3 using the projection device 1. That is, the physical objects of the three-dimensional terrain 3 are colored by projection to realize the dynamic physical representation of the three-dimensional terrain.

[0003] In recent years, projection-related technologies in my country have developed rapidly, evolving from the initial slide technology to current multi-center projection, interactive projection, and LED projection. Furthermore, accuracy and calibration technologies are constantly improving, and the projection surface has expanded from a flat plane to a curved surface. However, the object of projection is always a two-dimensional plane, or a curved surface that has been deformed for visual convenience. Using existing projection technologies to project onto three-dimensional terrain will result in distortion and poor projection effects.

[0004] Therefore, existing projection methods are not suitable for projecting three-dimensional terrain, and a technical solution for projecting three-dimensional models needs to be proposed. Summary of the Invention

[0005] The purpose of this application is to provide a three-dimensional projection method for dynamic sand tables, and to provide an effective technical solution for the dynamic projection of three-dimensional sand tables.

[0006] To achieve the above objectives, this application proposes a technical solution for a three-dimensional projection method for a dynamic sand table, comprising the following steps:

[0007] 1) Establish the image space coordinate system and the object space coordinate system; the image space coordinate system takes the projection center as the origin, the x and y axes are parallel to the image plane, and the z axis is perpendicular to the image plane; the object space coordinate system takes the center of the three-dimensional terrain bottom surface as the origin, the three-dimensional terrain bottom surface is the XOY plane where the X and Y axes are located, and the Z axis is perpendicular to the three-dimensional terrain bottom surface.

[0008] 2) Determine at least three pairs of non-coplanar and collinear position points on the image plane and the three-dimensional terrain bottom surface. Based on the coordinates of the image point on the image plane in the image space coordinate system and the coordinates of the object point on the three-dimensional terrain bottom surface in the object space coordinate system of each pair of position points, determine the coordinates of the projection center in the object space coordinate system. Use the Z-axis data of the projection center in the object space coordinate system as the distance from the projection center to the three-dimensional terrain bottom surface.

[0009] 3) Based on the coordinates of the projection center in the object space coordinate system, the size of the image, and the size of the three-dimensional terrain bottom surface, determine the offset between the perpendicular point from the projection center to the image plane and the center of the image plane. Use the offset as the image offset correction parameter to correct the image and obtain the corrected image plane. Use the corrected image plane as the projection image.

[0010] 4) Based on the principle of triangle similarity, establish the geometric relationship of each point on the 3D terrain, the distance from the projection center to the bottom surface of the 3D terrain, the orthophoto point of the orthophoto image, and the correction point corresponding to the orthophoto point; the orthophoto point is collinear with the object point on the bottom surface of the 3D terrain, the object point on the bottom surface of the 3D terrain corresponds one-to-one with the point on the 3D terrain, and the point on the 3D terrain is collinear with the correction point; the orthophoto image is a projection image used to project onto the bottom surface of the 3D terrain.

[0011] 5) Based on the position of the orthophoto point, the position of the correction point corresponding to the orthophoto point is obtained by combining the geometric relationship. The gray value of the orthophoto point is assigned to the corresponding correction point. All the correction points after assignment form a corrected image. The corrected image is then projected onto the three-dimensional terrain in three dimensions.

[0012] The beneficial effects of the three-dimensional projection method for the dynamic sand table of the present invention are as follows: The present invention determines the coordinates of the projection center in the object space coordinate system by at least three pairs of position points, and then obtains the image offset correction parameters by combining the size of the image and the size of the three-dimensional terrain bottom surface. The image is corrected according to the offset correction parameters. After correction, the correction point corresponding to each orthophoto point is solved by establishing the geometric relationship between the orthophoto and the corrected image. The gray value of the orthophoto point is assigned to the correction point. Projection is performed through the correction point, realizing a three-dimensional projection without deformation or distortion, thus improving the effect of three-dimensional projection.

[0013] Furthermore, the geometric relationship in step 4) is:

[0014]

[0015] Where (x0, y0, -f) are the coordinates of the orthophoto point in the image space coordinate system; (x, y, -f) are the coordinates of the correction point corresponding to the orthophoto point in the image space coordinate system; H is the distance from the projection center to the bottom surface of the 3D terrain; h is the height of the point on the 3D terrain corresponding to the object point on the bottom surface of the 3D terrain collinear with the orthophoto point; (x0, y0, -f) are the coordinates of the orthophoto point in the image space coordinate system ... correction point corresponding to the orthophoto point in the image space coordinate system; H is the distance from the projection center to the bottom surface of the 3D terrain; h is the height of the point on the 3D terrain corresponding to the object point on the bottom surface of the 3D terrain collinear with n y n ) represents the offset correction parameters for the image.

[0016] Furthermore, the image offset correction parameter (x) n y n )for:

[0017]

[0018]

[0019] Where, x max x represents the maximum x-axis value of the image point on the image plane in the image space coordinate system; min x is the minimum value of the image point on the image plane along the x-axis in the image space coordinate system; max -x min X is the length of the image plane along the x-axis; max X represents the maximum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the X-axis; min X represents the minimum value of the object point on the three-dimensional terrain base surface along the X-axis in the object space coordinate system; max -X min y is the length of the bottom surface of the three-dimensional terrain along the X-axis; max The maximum value of the y-axis of the image point on the image plane in the image space coordinate system; y min The minimum value of the y-axis of the image point on the image plane in the image space coordinate system; y max -y min Y is the length of the image plane along the y-axis; max Y represents the maximum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the Y-axis; min Y is the minimum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the Y-axis; max -Y min X represents the length of the bottom surface of the three-dimensional terrain along the Y-axis; s The x-axis represents the magnitude of the projection center in the object space coordinate system; the y-axis represents the magnitude of the projection center in the object space coordinate system. s The value of the Y-axis is the projection center in the object space coordinate system.

[0020] Furthermore, in order to more accurately determine the coordinates of the projection center in the object space coordinate system, in step 2), the coordinates of the projection center in the object space coordinate system are determined by using four sets of collinear equations composed of four pairs of position points, combined with the least squares method.

[0021] Furthermore, based on the principle of collinearity, the collinearity equations corresponding to each pair of points are as follows:

[0022]

[0023]

[0024] Among them, (X) s Y s Z s (X) represents the coordinates of the projection center in the object space coordinate system; A Y A Z A (x) represents the coordinates of point A on the three-dimensional terrain base in the object space coordinate system; a y a (f) represents the coordinates of image point a on the image plane in the image space coordinate system; image point a and object point A are a pair of position points; is the rotation matrix between the object space coordinate system and the image space coordinate system.

[0025] Furthermore, in order to obtain a more uniform corrected image, the method also includes a step of grayscale interpolation of the unevenly distributed image points in the corrected image.

[0026] Furthermore, to avoid trapezoidal projection, a trapezoidal correction step is included before solving for the image's offset correction parameters.

[0027] Furthermore, to improve the accuracy of trapezoidal correction, trapezoidal correction is performed using a gyroscope or a camera.

[0028] Furthermore, in order to obtain more accurate height values ​​for points on the 3D terrain, the height of each point on the 3D terrain is determined using DEM data. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the dynamic projection of the three-dimensional sand table according to the present invention;

[0030] Figure 2 This is a flowchart of the three-dimensional projection method for the dynamic sand table of the present invention;

[0031] Figure 3 This is a schematic diagram illustrating the establishment of the image space coordinate system and the object space coordinate system of the present invention;

[0032] Figure 4This is a schematic diagram showing the collinearity of image points on the image plane and object points on the three-dimensional terrain bottom surface.

[0033] Figure 5 This is a schematic diagram illustrating the solution for determining the position of the projection center in this invention;

[0034] Figure 6 This is a schematic diagram of the trapezoidal correction of the present invention;

[0035] Figure 7 This is a schematic diagram of the trapezoidal correction used to establish an equivalent image according to the present invention;

[0036] Figure 8 This is a schematic diagram illustrating the solution of the offset correction parameters for the image of the present invention;

[0037] Figure 9 This is a schematic diagram illustrating the solution of the image correction points in this invention;

[0038] In the diagram: 1 is the projection device, 2 is the image, 3 is the three-dimensional terrain, 4 is the trapezoidal corrected image, 5 is the equivalent image, 6 is the vertical line, and 7 is the center line of the projection beam. Detailed Implementation

[0039] Example of a 3D projection method for dynamic sand table:

[0040] The main concept of this invention is that, in order to achieve three-dimensional projection, this invention determines the image offset correction parameters by solving the position of the projection center in the object space coordinate system. After the image is offset corrected by the image offset correction parameters, the geometric relationship between the orthophoto and the corrected image is established by combining the principle of triangle similarity. The correction point corresponding to each orthophoto point is determined by the geometric relationship, and the gray value of each orthophoto point is assigned to the corresponding correction point. Three-dimensional projection is achieved by correcting the image.

[0041] Specifically, the three-dimensional projection method of the dynamic sand table is as follows: Figure 2 As shown, it includes the following steps:

[0042] 1) Establish the image space coordinate system and the object space coordinate system.

[0043] To better describe the spatial positions of the image points (image 2 in projection device 1) and the three-dimensional terrain, and to establish the geometric relationship between the image points and points on the terrain, coordinate systems are established for both, such as... Figure 3 As shown:

[0044] The image space coordinate system is established with the projection center S of the image as the origin. The z-axis is perpendicular to the image plane, and the x and y axes satisfy the right-hand rule and are parallel to the image plane. The image space coordinate system is denoted as S-xyz.

[0045] The object space coordinate system is established with the center point O of the three-dimensional terrain bottom surface as the origin. Its Z-axis is perpendicular to the three-dimensional terrain bottom surface, and the XOY plane where the X and Y axes are located is the three-dimensional terrain bottom surface. The object space coordinate system is denoted as O-XYZ.

[0046] 2) Set the rotation matrices for the image space coordinate system and the object space coordinate system.

[0047] To achieve the transformation of vectors in space between two coordinate systems, a rotation matrix is ​​introduced. Based on the rotation matrix, the vector from the projection center S in both coordinate systems to the image point a is... The coordinate transformation formula is as follows:

[0048]

[0049] in, and Let be the coordinates of image point a and projection center S in the object space coordinate system, respectively. Let a be the coordinates of image point a in the image space coordinate system, and let a1, a2, a3, b1, b2, b3, c1, c2, c3 be the rotation parameters of the rotation matrix R.

[0050] 3) Calculate the coordinates of the projection center in the object space coordinate system based on four pairs of non-coplanar and collinear position points; each pair of position points includes the image point on the image plane and the corresponding object point on the three-dimensional terrain bottom surface.

[0051] Collinearity here refers to the fact that image points on the image plane, the corresponding object points on the 3D terrain surface, and the projection center are all on a straight line. Based on the collinearity condition, it can be known that, for example... Figure 4 As shown, let point A be the projection of image point a onto the terrain. Then we have λ is the proportionality coefficient, based on as well as The geometric relationship between the coordinates of image point a in the image space coordinate system and the coordinates of the projection point A in the object space coordinate system is as follows:

[0052]

[0053] By deforming the geometric relationship to eliminate the proportionality coefficient λ, we obtain:

[0054]

[0055]

[0056] The modified formula described above is the collinearity equation in photogrammetry, where the coordinates of the projection point A in the object space coordinate system are (X, Y, X). A ,Y A ZA Manual measurement is required. During the tilt and misalignment correction phase, to facilitate measurement and calculation, such as... Figure 5 The diagram shows how to project the terrain onto a two-dimensional plane, or how to set the dynamic terrain to a planar state, i.e., a planar state where Z=0, and only measure the points on that plane, i.e., the object points on the bottom surface of the three-dimensional terrain.

[0057] Define the positions of image points (any four points, satisfying the condition of non-collinearity) on the image plane, project them onto the Z=0 plane, and measure the coordinates of the projected points on this plane. A The value is 0. Substituting the coordinates of the four projection points (i.e., object points) on the measured 3D terrain surface in the object space coordinate system and the coordinates of the four collinear image points in the image space coordinate system into the collinearity condition equation, we obtain eight independent equations. Solving these equations using the least squares method yields the coordinates (X, X) of the projection center S in the object space coordinate system. S ,Y S Z S This gives the position of the projection center. Regarding the rotation matrix... It is not necessary to solve for these parameters, as they have already been canceled out during the process of determining the location of the projection center.

[0058] The process of calculating the coordinates of the projection center in the object space coordinate system by using the least squares method for each pair of position points is existing technology and will not be elaborated here.

[0059] Of course, as another implementation method, the coordinates of the projection center in the object space coordinate system can also be solved by using three pairs of position points, where the three points on the image plane are not collinear.

[0060] 4) Perform trapezoidal correction on projection device 1 to obtain an equivalent image of the original image (i.e., the trapezoidal corrected image).

[0061] In the daily use of a projector, the center ray of the projection must be perpendicular to the projection screen to ensure a good projection effect. If the two cannot be guaranteed to be perpendicular, problems such as... Figure 6 As shown, the image appears trapezoidal, and in this case, trapezoidal correction is required.

[0062] Trapezoidal correction is divided into automatic correction and manual correction.

[0063] Automatic correction methods include:

[0064] (1) Correction via gyroscope. When the projector tilts, the aspect ratio of the projected rectangular image can be automatically corrected based on the relative offset of the gyroscope position;

[0065] (2) Correction via camera. A solid color image projected by the projector is acquired via camera, and the tilt parameters and tilt angle are calculated based on this image. Then, trapezoidal correction is performed based on the calculated tilt angle.

[0066] The process of trapezoidal correction is existing technology and will not be described in detail here. After trapezoidal correction, the rotation matrix R can also be eliminated.

[0067] After trapezoidal correction, the projected image changes from trapezoidal to rectangular. At this point, the image inside the projector is equivalent to being parallel to the projection plane, thus establishing... Figure 7 The equivalent image 5 shown is shown above, while the trapezoidal corrected image 4 is the original image. Figure 7 The projection center S intersects the bottom surface via the perpendicular line 6, with point N being the perpendicular point. The projection beam centerline 7 of projection device 1 passes through the center of the equivalent image 5 and the bottom surface. The equivalent image and the projection bottom surface are parallel and similar, which is crucial for subsequent image correction. Because the equivalent image and the projection bottom surface are parallel and similar, the focal length of the equivalent image can be customized.

[0068] 5) Solve for the offset correction parameters of the equivalent image 5 (hereinafter referred to as the image for ease of description), correct the image using the offset correction parameters, and obtain the corrected image plane. Use the corrected image plane as the projection image.

[0069] like Figure 8 The diagram shows a schematic of the projection after trapezoidal correction. The image plane and the bottom surface of the three-dimensional terrain are parallel. S is the projection center, n is the perpendicular point of the projection center on the image plane, o is the center of the image plane, N is the perpendicular point of the projection center on the bottom surface of the three-dimensional terrain, and O is the center of the bottom surface of the three-dimensional terrain.

[0070] Let the length of line segment no in the x-direction be x. n The length of line segment no in the y direction is y. n , (x n y n This refers to the image offset correction parameter, where the length of line segment NO in the X direction is X. N (That is, the value of point N on the X-axis in the object space coordinate system), the length of line segment NO in the Y direction is Y. N (That is, the value of the Y-axis of point N in the object space coordinate system), based on the principle of triangle similarity, we can obtain:

[0071]

[0072]

[0073] And because X N =X S Y N =YS ,get:

[0074]

[0075]

[0076] Where, x max x represents the maximum x-axis value of the image point on the image plane in the image space coordinate system; min x is the minimum value of the image point on the image plane along the x-axis in the image space coordinate system; max -x min X is the length of the image plane along the x-axis; max X represents the maximum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the X-axis; min X represents the minimum value of the object point on the three-dimensional terrain base surface along the X-axis in the object space coordinate system; max -X min y is the length of the bottom surface of the three-dimensional terrain along the X-axis; max The maximum value of the y-axis of the image point on the image plane in the image space coordinate system; y min The minimum value of the y-axis of the image point on the image plane in the image space coordinate system; y max -y min Y is the length of the image plane along the y-axis; max Y represents the maximum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the Y-axis; min Y is the minimum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the Y-axis; max -Y min X represents the length of the bottom surface of the three-dimensional terrain along the Y-axis; s Let X be the magnitude of the projection center S in the object space coordinate system; Y be the magnitude of the projection center S along the X-axis. s Let S be the size of the Y-axis in the object space coordinate system of the projection center S.

[0077] As can be seen from the above formula, based on the coordinates of the projection center in the object space coordinate system, as well as the size of the image and the size of the three-dimensional terrain bottom surface, the offset of the perpendicular point from the projection center to the image plane and the center of the image plane is determined. The offset is the image offset correction parameter.

[0078] 6) Based on the principle of triangle similarity, establish the geometric relationship between the height of each point on the three-dimensional terrain, the distance from the projection center to the bottom of the three-dimensional terrain, the orthophoto point of the orthophoto, and the correction point corresponding to the orthophoto point.

[0079] The projected image determined in step 5) above can be used as an orthophoto or it can be corrected and used as a corrected image. The orthophoto is the projected image used to project onto the bottom surface of the three-dimensional terrain; the subsequent corrected image is the projected image used to project onto the three-dimensional terrain.

[0080] Let the coordinates of the orthophoto point in the image space coordinate system be (x0, y0, -f), and the coordinates of the corresponding correction point in the image space coordinate system be (x, y, -f). Let the height of a point on the 3D terrain be h, where h has different values ​​for different (X, Y) coordinates. Let (X, Y) be the coordinates of the object point on the 3D terrain surface in the object space coordinate system. Let the vertical distance from the projection center S to the bottom surface of the 3D terrain be H, i.e., H = Z. s f is the focal length, the image is an equivalent image, and the focal length is customizable.

[0081] from Figure 9 It can be seen that the relationship between the correction point and the orthophoto point is as follows: the orthophoto point is collinear with the object point on the bottom surface of the 3D terrain; the object point on the bottom surface of the 3D terrain corresponds one-to-one with the point on the 3D terrain; and the point on the 3D terrain is collinear with the correction point. The height h of the point on the 3D terrain is determined using DEM data, based on elevation data (digital elevation model). The 3D terrain model is a scaled-down version of the real 3D geography, and the height of the point on the 3D terrain is determined by a scaling factor. Of course, the height can also be directly measured, and this invention does not impose any limitations on this.

[0082] Let the geometric relationship between the orthophoto points and the corresponding correction points of an orthophoto image be:

[0083]

[0084] like Figure 9 As shown, based on the principle of similar triangles, we obtain:

[0085]

[0086] It is deduced that, Similarly, we can obtain

[0087] That is, the geometric relationship is:

[0088]

[0089] Since h is a function of (X,Y), and (X,Y) is proportional to (x0,y0), we can obtain:

[0090]

[0091] Because the projector has performed offset and trapezoidal corrections, the tilted projected image is equivalent to an equivalent image parallel to the bottom surface. Introducing the image offset correction parameters into the geometric relationships, the geometric relationship between the orthophoto and the corrected image is obtained as follows:

[0092]

[0093] Where (x0, y0, -f) are the coordinates of the orthophoto point in the image space coordinate system; (x, y, -f) are the coordinates of the correction point corresponding to the orthophoto point in the image space coordinate system; H is the distance from the projection center to the bottom surface of the 3D terrain; h is the height of the point on the 3D terrain corresponding to the object point on the bottom surface of the 3D terrain collinear with the orthophoto point; (x0, y0, -f) are the coordinates of the orthophoto point in the image space coordinate system ... correction point corresponding to the orthophoto point in the image space coordinate system; H is the distance from the projection center to the bottom surface of the 3D terrain; h is the height of the point on the 3D terrain corresponding to the object point on the bottom surface of the 3D terrain collinear with n y n ) represents the offset correction parameters for the image.

[0094] 7) Substitute the position (x0, y0) of the orthophoto point of the orthophoto into the geometric relationship obtained in step 6) above, and solve for the position (x, y) of the corresponding correction point.

[0095] 8) Assign the gray value of the orthophoto point to the corresponding correction point. All the correction points after assignment form the corrected image.

[0096] The assignment process is as follows:

[0097] p(x,y)=p(x0,y0);

[0098] Where p is a function of gray value with respect to image point position, (x,y) is the position of the corrected image point, and (x0,y0) is the position of the orthophoto point. The two satisfy the geometric relationship between the orthophoto and corrected image points in the forward method.

[0099] 9) Perform grayscale interpolation on the unevenly distributed image points in the corrected image, and then perform three-dimensional projection on the corrected image after grayscale interpolation.

[0100] The pixels in the corrected image obtained through the above steps are irregularly arranged, and there may be blank areas without pixels. In some areas, multiple pixels may overlap, meaning that the pixel distribution in the obtained corrected image is uneven. Therefore, grayscale interpolation is required to create an image with a uniform pixel distribution.

[0101] This invention solves for the correction point corresponding to the orthophoto point, assigns the grayscale of the orthophoto point to the correction point, and projects the image onto the three-dimensional terrain. This avoids the offset caused by two-dimensional projection technology when projecting onto three-dimensional terrain, and achieves accurate matching between the image and the three-dimensional terrain.

Claims

1. A three-dimensional projection method of a dynamic sand table, characterized by, Includes the following steps: 1) Establish the image space coordinate system and the object space coordinate system; the image space coordinate system takes the projection center as the origin, the x and y axes are parallel to the image plane, and the z axis is perpendicular to the image plane; the object space coordinate system takes the center of the three-dimensional terrain bottom surface on the sand table as the origin, the three-dimensional terrain bottom surface is the XOY plane where the X and Y axes are located, and the Z axis is perpendicular to the three-dimensional terrain bottom surface. 2) Determine at least three pairs of non-coplanar and collinear position points on the image plane and the three-dimensional terrain bottom surface. Based on the coordinates of the image point on the image plane in the image space coordinate system and the coordinates of the object point on the three-dimensional terrain bottom surface in the object space coordinate system, determine the coordinates of the projection center in the object space coordinate system. Use the Z-axis coordinate of the projection center in the object space coordinate system as the distance from the projection center to the three-dimensional terrain bottom surface. 3) Based on the coordinates of the projection center in the object space coordinate system, the size of the image, and the size of the three-dimensional terrain bottom surface, determine the offset between the perpendicular point from the projection center to the image plane and the center of the image plane. Use the offset as the image offset correction parameter to correct the image and obtain the corrected image plane. Use the corrected image plane as the projection image. 4) Based on the principle of triangle similarity, establish the geometric relationship of each point on the 3D terrain, the distance from the projection center to the bottom surface of the 3D terrain, the orthophoto point of the orthophoto image, and the correction point corresponding to the orthophoto point; the orthophoto point is collinear with the object point on the bottom surface of the 3D terrain, the object point on the bottom surface of the 3D terrain corresponds one-to-one with the point on the 3D terrain, and the point on the 3D terrain is collinear with the correction point; the orthophoto image is the projection image used to project onto the bottom surface of the 3D terrain; the correction image is the projection image used to project onto the 3D terrain. 5) Based on the position of the orthophoto point, the position of the correction point corresponding to the orthophoto point is obtained by combining geometric relationships. The gray value of the orthophoto point is assigned to the corresponding correction point. All the correction points after assignment form a correction image. The correction image is then projected onto the three-dimensional terrain in three dimensions to color the physical objects of the three-dimensional terrain, so as to realize the dynamic physical representation of the three-dimensional terrain.

2. The method of claim 1, wherein, The geometric relationship in step 4) is as follows: ； Where f is the focal length. The coordinates of the orthophoto point in the orthophoto image within the image space coordinate system; The coordinates of the image correction point corresponding to the orthophoto point in the image space coordinate system; Let be the distance from the projection center to the bottom surface of the three-dimensional terrain. The height of a point on the 3D terrain corresponding to the object point on the 3D terrain base collinear with the orthophoto point. These are the offset correction parameters for the image. Let be the length of line segment 'no' in the x-direction. Let be the length of line segment no in the y direction, n be the perpendicular point of the projection center to the image plane, and o be the center of the image plane.

3. The method of three-dimensional projection of a dynamic sand table according to claim 1 or 2, characterized in that, Shift correction parameters for photographs are: ； ； in, The maximum value of the image point on the image plane in the image space coordinate system along the x-axis; It represents the minimum x-axis value of the image point on the image plane in the image space coordinate system; The length of the image plane along the x-axis; This represents the maximum value of the X-axis of the object point on the bottom surface of the three-dimensional terrain in the object space coordinate system; It represents the minimum value of the X-axis of the object point on the three-dimensional terrain bottom surface in the object space coordinate system; The length of the bottom surface of the three-dimensional terrain along the X-axis; This represents the maximum value of the y-axis of the image point on the image plane in the image space coordinate system; It represents the minimum value of the y-axis of the image point on the image plane in the image space coordinate system; The length of the image plane along the y-axis; This represents the maximum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the Y-axis. It represents the minimum value of the object point on the three-dimensional terrain bottom surface in the object space coordinate system along the Y-axis; This represents the length of the bottom surface of the three-dimensional terrain along the Y-axis. The magnitude of the X-axis of the projection center in the object space coordinate system; The value of the Y-axis of the projection center in the object space coordinate system; Let be the length of line segment 'no' in the x-direction. Let be the length of line segment no in the y direction, n be the perpendicular point of the projection center to the image plane, and o be the center of the image plane.

4. The method of claim 1, wherein, In step 2), the coordinates of the projection center in the object space coordinate system are determined by using four sets of collinear equations composed of four pairs of position points, combined with the least squares method.

5. The method of claim 4, wherein the dynamic sand table is a three-dimensional projection. For each pair of points, the collinear equations are: ； ； in, The coordinates of the projection center in the object space coordinate system; Let A be the coordinates of point A on the three-dimensional terrain base in the object space coordinate system; Let be the coordinates of image point a on the image plane in the image space coordinate system; image point a and object point A are a pair of position points; Let be the rotation matrix between the object space coordinate system and the image space coordinate system, and let a1, a2, a3, b1, b2, b3, c1, c2, c3 be the rotation parameters.

6. The method of claim 1, wherein, It also includes the step of grayscale interpolation of unevenly distributed image points in the corrected image.

7. The method of claim 1, wherein the dynamic sand table is a three-dimensional projection. The process of determining the offset correction parameters of the image also includes a trapezoidal correction step.

8. The method of claim 7, wherein the dynamic sand table is a three-dimensional projection. Trapezoidal correction is performed using a gyroscope or camera.

9. The method of claim 1, wherein, The height of each point on the 3D terrain is determined using DEM data.

Images