Target vertex, zero elevation point and image bottom point height measurement method based on area array inclined image
By utilizing the spatial relationship between the target vertex, zero elevation point, and image base point in remote sensing images, and combining it with a vertical reference image, the problem of the target base point being invisible in remote sensing images was solved, enabling elevation measurement of area array tilted images and improving measurement accuracy.
Patent Information
- Application Number
- CN202510525757.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-25
- Publication Date
- 2025-10-31
AI Technical Summary
In remote sensing images, when the target's base point is not visible, existing technologies struggle to effectively measure elevation.
By utilizing the spatial relationship between the target vertex, zero elevation point, and image base point in the image to be measured and the orthophoto reference image, the elevation is measured by calculating the distance from the top image point to the image base point and the projection error, combined with the vertical reference image.
In area array tilted images, the elevation of the target can be accurately measured. It is applicable to the conditions of visible target vertices and zero elevation points, and does not depend on ground spatial resolution, thus improving measurement accuracy.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of aviation image processing technology. Background Technology
[0002] Height information, as a crucial attribute of target information, is an important parameter for urban economic activities and military applications. Currently, target elevation measurement based on remote sensing images is one of the important methods of height measurement, which can be broadly divided into two categories: stereo image pair height measurement and single-image height measurement. Single-image height measurement mainly utilizes target shadow features or information such as vertical image point displacement, but both require the target's vertices and basal points to be visible in the image. In actual remote sensing processes, situations often arise where the target's basal points are not visible in the image. Summary of the Invention
[0003] The purpose of this invention is to propose a height measurement method based on the target vertex, zero elevation point, and image base point of an area array tilted image by utilizing the spatial relationship between the target vertex, zero elevation point, and image base point in the image to be measured and the orthophoto reference image.
[0004] The steps of this invention are: S1. Assume target AB is perpendicular to the ground, point A is the top of the target, point B is the bottom of the target, the target elevation is h, the imaging height is H, and the image points of points A and B are image points a and b, respectively. p And image point b p ; S2, Target elevation h is determined by platform height H and target top image point a. p To the bottom point o p Distance r0, top image point a of the target p To the bottom image point b p Distance δ h get: S3, Target top image point a p To the bottom point o p Determining the distance r0 Let point C be the zero elevation point, and point O be the ground level. On the inclined imaging plane, let image points be image point a, image point b, image point c, and image point o. On the vertical imaging plane, let image point a be the image point. p Like point b p Like point c p and o p ; S4, the coordinates of the camera center are (X S ,Y S Z S The target point coordinates are (X, Y, Z), and the corresponding image point coordinates are (x, y, –f). According to the photographic imaging equation, the coordinates of the three points have the following relationship: In the formula, a j b j c j These are elements in the coordinate rotation matrix, where j = 1, 2, 3; S5. The elements in the coordinate rotation matrix are obtained by the following formula: In the formula, It is based on the Y-axis as the principal axis. The corner elements of the three outer orientation elements in the system, ω is the heading angle (pitch angle), ω is the side tilt angle, and κ represents the image rotation angle; S6. When the platform height is H, then Z S =H; the elevation of the orthophoto transformation of the tilted image is (Hf), then Z = Hf, and the coordinates of the top image point a of the target (x) are... a ,y a Substituting into equation (3), we can obtain the coordinates (x, y) of the orthographic projection of the top image point a of the target in the tilted image. ap ,y ap ): S7. The image base point o in the tilted image becomes the image base point o after orthographic projection. p The coordinates are Therefore, after orthographic projection, the top image point a of the target p The base point o of the orthographic projection p distance l opap for: S8, Projection error δ h Determination: Introducing a vertical reference image, with top image points a and a2, bottom image points o and o2, and zero elevation points c and c2, the tilted image is transformed by vertical projection to obtain the lengths l on the vertical projection planes of oa and oc. opap and l opcp In the vertical reference image, the top image point a2 and the bottom image point b2 of the target overlap, and the length l of o2b2 is measured. o2b2 and o2c2 length l o2c2 Therefore, l opbp l opcp l o2b2 and l o2c2 The following relationship exists: Therefore Therefore, it can be seen from the image The obtained r o δ h Substituting into equation (1) completes the target elevation measurement.
[0005] This invention effectively solves the problem of target height measurement when using a tilted area image (visible target vertex, zero elevation point, and image base point) in conjunction with a vertical reference image (ground spatial resolution is not required). Attached Figure Description
[0006] Figure 1 This is a schematic diagram of image point displacement in a vertical image; Figure 2 This is a schematic diagram of the vertical projection of an oblique image; Figure 3 This is a schematic diagram of feature point selection, where the left side is the tilted measurement image and the right side is the vertical reference image; Figure 4 This is a schematic diagram of feature point selection for a right-tilted image, where the left side is the tilt measurement image and the right side is the vertical reference image. Detailed Implementation
[0007] This invention proposes a three-point height measurement method based on an area array tilted image, utilizing the spatial relationship between the target vertex, zero elevation point, and image base point in the image to be measured and the orthophoto reference image. This method effectively solves the problem of target height measurement when using an area array tilted image (with visible target vertex, zero elevation point, and image base point) in conjunction with a vertical reference image (without requiring specific ground spatial resolution).
[0008] I. Basic Principles In the vertical imaging process of the area array, the target AB is perpendicular to the ground, point A is the top of the target, point B is the bottom of the target, the target elevation is h, and the imaging height is H. The image points of points A and B are image points a and b, respectively. p And image point b p .
[0009] According to the principle of similar triangles, from Figure 1 From this, we can see that the target elevation h can be determined by the platform height H and the top image point a of the target. p To the bottom point o p Distance r0, top image point a of the target p To the bottom image point b p Distance δ h The calculation yields the result shown in equation (1):
[0010] Therefore, in a tilted array image, only r0 and δ need to be calculated. h The target elevation h can then be calculated by substituting it into equation (1).
[0011] (a) Target top image point a p To the bottom point o p Determining the distance r0 Tilt imaging of array such as Figure 2 As shown, point A is the top of the target, point B is the bottom of the target, point C is the zero elevation point, and point O is the ground level. On the inclined imaging plane, the image points are image point a, image point b, image point c, and image point o, respectively. On the vertical imaging plane, the image point is image point a. p Like point b p Like point c p and o p .
[0012] In the ground photogrammetric coordinate system, let... Figure 2 The coordinates of the center of the central photography are (X S ,Y S Z S The target point coordinates are (X, Y, Z), and the corresponding image point coordinates are (x, y, –f). According to the photographic imaging equation, the coordinates of the three points have the following relationship: In the formula, a j b j c j (j=1,2,3) are elements in the coordinate rotation matrix.
[0013] The elements in the coordinate rotation matrix are determined by the exterior orientation elements of the camera, as shown in equation (4): In the formula, It is based on the Y-axis as the principal axis. The corner elements of the three outer orientation elements in the system, ω represents the heading angle (pitch angle), ω represents the side roll angle (roll angle), and κ represents the image rotation angle (yaw angle). The sign of the turning angle is selected according to Chinese regulations. Angles are positive when rotated clockwise, and positive when rotated counterclockwise, i.e., pitching up, rolling to the right, and yawing to the left.
[0014] from Figure 2 It can be seen that the platform height is H, then Z S =H; the elevation of the orthophoto transformation of the tilted image is (Hf), then Z = Hf. The coordinates (x, y) of the top image point a of the target are... a ,y a Substituting into equation (3), we can obtain the coordinates (x, y) of the orthographic projection of the top image point a of the target in the tilted image. ap ,y ap )
[0015] from Figure 3 It can be seen that the image base point o in the tilted image, after orthographic projection, becomes the image base point o. p The coordinates are Therefore, after orthographic projection, the top image point a of the target p The base point o of the orthographic projection p distance l opap (Right now Figure 1 r0) is:
[0016] (ii) Projection error δ h Since the bottom image point of the target is not visible in the tilted array image, δ cannot be calculated. h Therefore, a vertical reference image is introduced. In the oblique measurement image and the vertical reference image, the top image points a, a2, the bottom image points o, o2, and the zero elevation points c, c2 are respectively located, as follows: Figure 3 As shown.
[0017] Transform the tilted image through vertical projection (e.g.) Figure 2 As shown), the lengths l on the perpendicular projection planes of oa and oc can be calculated. opap and l opcp Since the bottom image point b of the target is not visible, the length l of ob cannot be calculated. opbp .
[0018] In the vertical reference image, the top image point a2 and the bottom image point b2 of the target overlap, and the length l of o2b2 can be measured. o2b2 and o2c2 length l o2c2 .
[0019] from Figure 2 It can be seen from l opbp l opcp l o2b2 and l o2c2 The following relationship exists:
[0020] Therefore
[0021] from Figure 3 It can be seen from this:
[0022] The calculated r o δ hSubstituting into equation (1) will complete the target elevation measurement. This is the basic principle of the elevation measurement method for a single tilted array image where only the target vertex is visible.
[0023] II. Measurement Process 1. Read in data The input data includes image data I of the target elevation to be measured, auxiliary parameters, and a reference image. The auxiliary parameters include six items: flight altitude H, camera pitch angle α, camera roll angle ω, focal length f, point distance d, and tilt direction F.
[0024] 2. Calculate the coordinate rotation matrix Substitute the camera pitch angle α, camera roll angle ω, and camera yaw angle κ (which can be ignored and set to 0) into equation (4) to calculate the element a in the coordinate rotation matrix. j b j c j (j=1,2,3) values.
[0025] 3. Calculate the coordinates of the image base point. from Figure 2 It can be seen that the coordinates of the ground point corresponding to the image base point in the ground photogrammetric coordinate system are (X... S ,Y S Substituting ,0) into equation (2), we can obtain the coordinates of the base point as:
[0026] 4. Establish the location and coordinates of the corresponding image points. (1) Establish the image plane coordinate system Determine the platform's flight direction in the tilted image based on the tilt direction F. Determine the x-axis along the flight direction and the y-axis using the right-hand rule. Figure 4 The left side shows the coordinate settings for the right-tilted image.
[0027] (2) Determine the position and coordinates of the target vertex a, the zero elevation point c, and the image base point o. The coordinates (x, y) of the image base point o obtained according to step 3 (10) o ,y o Mark the position of the image base point o in the tilted image.
[0028] Then, in the oblique image, the top image point a and the zero elevation point c of the target to be measured are determined, and their row and column coordinates (m) are determined. a ,n a ), (m c ,n c ).
[0029] According to formula (11), the row and column coordinates (m) of the top image point a and the zero elevation point c of the target are calculated. a ,n a), (m c ,n c Convert ) to point coordinates (x) in a spatial coordinate system a ,y a ), (x c ,y c ).like Figure 4 As shown on the left: Where: m, n—the number of rows and columns of the image point in the digital image; M0, N0—the number of row and column centers of the digital image; d x d y — The pixel spacing in the row and column directions of a digital image.
[0030] (3) Establish the position and coordinates of the corresponding image points in the reference image. Comparing the top image point a, zero elevation point c, and bottom image point o in the tilted image, find the corresponding image point positions a1, c1, and o1 in the vertical reference image, and their corresponding coordinates (m). a1 ,n a1 ), (m c1 ,n c1 ) and (m o1 ,n o1 ),like Figure 4 As shown on the right.
[0031] 5. Calculate the distance l between the image point and the image base point of the target height to be measured. opap (r0) The elements of the coordinate rotation matrix calculated in step 2 and the coordinates (x, y, y) of the top image point a of the target to be measured, established in step 4, are then compared. a ,y a Substituting into equation (6), we obtain the distance l. opap (Right now Figure 1 (r0).
[0032] 6. Calculate the distance l between the zero elevation point and the image base point in the oblique image. opcp Combine the element values of the coordinate rotation matrix calculated in step 2 with the coordinates (x, y) of the zero elevation point c established in step 4. c ,y c Substituting into equation (6), we obtain the radiation distance l at the zero elevation point. opcp .
[0033] 7. Determine l in the tilted image opbp The (m) determined in step 4 o2 ,n o2 ), (m b2 ,n b2 ), (m c2 ,nc2 ), then l can be obtained o2b2 l o2c2 As shown in equation (12)
[0034] The l calculated in step 6 opcp Substituting equation (12) into equation (8), we get l opbp As shown in equation (13)
[0035] 8. Calculate the projection error δ h The l calculated in step 5 opap (r0), l calculated in step 7 opbp Substituting into equation (9), we obtain the projection error δ. h .
[0036] 9. Calculate the target elevation h The flight altitude H and the l calculated in step 5 are used. opap (r0), the projection error δ calculated in step 8 h Substituting into equation (1), the elevation h of the target is calculated.
[0037] III. Instructions for Use (1) This method is applicable to area array tilted images where the target vertex, zero elevation point and image base point are visible at the same time, without considering whether the image base point of the target is visible.
[0038] (2) This method is applicable not only to target height measurement in tilted area array images, but also to target height measurement in vertical area array images. However, the target image point to be measured in the vertical area array image cannot be located at the image bottom point, and the greater the distance between the top image point and the image bottom point, the higher the height measurement accuracy.
[0039] (3) This method requires the assistance of a reference image. It is only required that the reference image be a vertical reference image, and it is not required whether the ground spatial resolution is known.
[0040] (4) This method requires the camera pitch angle α and camera roll angle ω. If these two parameters are not recorded, they can be converted based on the platform pitch angle α, roll angle ω, camera mounting angle and other parameters.
[0041] (5) All three methods require the dot pitch d parameter of the CCD photosensitive unit. To improve accuracy, it is recommended to use... CCD photosensitive unit width l m and length l n The number of rows M and columns N of the CCD photosensitive units are calculated according to formula (14):
Claims
1. A method for measuring the height of a target vertex, zero elevation point, and image base point based on a tilted area array image, characterized in that: The steps are as follows: S1. Assume target AB is perpendicular to the ground, point A is the top of the target, point B is the bottom of the target, the target elevation is h, the imaging height is H, and the image points of points A and B are image points a and b, respectively. p And image point b p ; S2, Target elevation h is determined by platform height H and target top image point a. p To the bottom point o p Distance r0, top image point a of the target p To the bottom image point b p Distance δ h get: S3, Target top image point a p To the bottom point o p Determining the distance r0 Let point C be the zero elevation point, and point O be the ground level. On the inclined imaging plane, let image points be image point a, image point b, image point c, and image point o. On the vertical imaging plane, let image point a be the image point. p Like point b p Like point c p and o p ; S4, the coordinates of the camera center are (X S ,Y S Z S The target point coordinates are (X, Y, Z), and the corresponding image point coordinates are (x, y, –f). According to the photographic imaging equation, the coordinates of the three points have the following relationship: In the formula, a j b j c j These are elements in the coordinate rotation matrix, where j = 1, 2, 3; S5. The elements in the coordinate rotation matrix are obtained by the following formula: In the formula, It is based on the Y-axis as the principal axis. The corner elements of the three outer orientation elements in the system, ω is the heading angle (pitch angle), ω is the side tilt angle, and κ represents the image rotation angle; S6. When the platform height is H, then Z S =H; the elevation of the orthophoto transformation of the tilted image is (Hf), then Z = Hf, and the coordinates of the top image point a of the target (x) are... a ,y a Substituting into equation (3), we can obtain the coordinates (x, y) of the orthographic projection of the top image point a of the target in the tilted image. ap ,y ap ): S7. The image base point o in the tilted image becomes the image base point o after orthographic projection. p The coordinates are Therefore, after orthographic projection, the top image point a of the target p The base point o of the orthographic projection p distance l opap for: S8, Projection error δ h Determination: Introducing a vertical reference image, with top image points a and a2, bottom image points o and o2, and zero elevation points c and c2, the tilted image is transformed by vertical projection to obtain the lengths l on the vertical projection planes of oa and oc. opap and l opcp In the vertical reference image, the top image point a2 and the bottom image point b2 of the target overlap, and the length l of o2b2 is measured. o2b2 and o2c2 length l o2c2 Therefore, l opbp l opcp l o2b2 and l o2c2 The following relationship exists: Therefore Therefore, it can be seen from the image The obtained r o δ h Substituting into equation (1) completes the target elevation measurement.