CN113532473B - Image pickup measurement error suppression method by arranging near-field stationary points - Google Patents
Image pickup measurement error suppression method by arranging near-field stationary points Download PDFInfo
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- 238000005259 measurement Methods 0.000 title claims abstract description 53
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- G—PHYSICS
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- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C25/00—Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass
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Abstract
The invention provides a camera measurement error suppression method by arranging near-field fixed points, which comprises the following steps: (1) Installing a marker, erecting a digital camera, and arranging a near-field stationary reference point; (2) Monitoring a far field structural mark and a near field reference mark simultaneously through a digital camera; (3) calibrating the digital camera; (4) Acquiring pixel coordinates of a far-field structural mark and a near-field reference mark; (5) obtaining displacement variation in a pixel coordinate system; (6) repeating the processing of step (5) for subsequent image sequences; (7) designing an adaptive filter to eliminate measurement errors; (8) obtaining the real displacement of the structure to be tested; the invention overcomes the defect that a far-field motionless reference point is difficult to arrange and find in the camera measurement so as to inhibit errors, and flexibly adapts to the requirements of the actual environment on the measurement angle and the field of view; an adaptive filtering technology is introduced, so that the measurement displacement is more accurate.
Description
Technical Field
The invention relates to the technical field of image pickup measurement, in particular to an image pickup measurement error suppression method by arranging near-field fixed points.
Background
Along with the development and progress of computer vision, image sensor and other technologies, the imaging measurement method with the characteristics of non-contact, long distance, high precision and the like gradually becomes one of research hotspots in the field of structural health monitoring. The measurement results of the structural displacement usually generate larger errors due to the factors of external environment, measuring instruments and the like. In order to suppress the influence of measurement errors on measurement accuracy, some people adopt a method of arranging stationary reference points near a structure to be measured or taking remote building groups as stationary reference points. Compared with the method for establishing a correlation model of single factors and measurement errors to achieve the inhibition effect, the method considers errors under the condition of multi-factor coupling and is more comprehensive. But this approach makes it difficult to arrange or find stationary reference points near the structure for environmental and field of view reasons for some situations, such as measuring mid-span deflection of a large-span bridge, high-rise vertices displacement. Therefore, a new method for suppressing the image capturing measurement error is needed, which is convenient to find the stationary reference point and is suitable for the field of view and the environmental requirements.
For example, the publication number CN106482648a of the "device and method for absolute detection of small displacement in a long-distance plane based on a fixed point" disclosed in the chinese patent literature includes a first signpost, a second signpost, and a camera, and the projection of the signpost is collected by the camera to detect movement, which has a great requirement on the arrangement of the reference point, limits the range of the structure to be detected, has low universality, cannot automatically adjust the measurement parameters, has low accuracy, and has large measurement error.
Disclosure of Invention
Therefore, the invention provides the camera measurement error suppression method by arranging the near-field stationary points, which can conveniently arrange the stationary reference points, suppress the measurement error under multi-factor coupling, meet the requirements of a remote measurement structure and flexibly adapt to the measurement environment.
In order to achieve the above object, the present invention provides the following technical solutions:
An image capturing measurement error suppressing method by disposing near-field stationary points, comprising the steps of:
(1) Installing far-field structure marks on a structure to be tested, selecting a static field to erect a digital camera, and setting a static marker between the digital camera and the structure to be tested, wherein near-field reference marks are arranged on the static marker;
(2) Adjusting parameters of the digital camera to enable the digital camera to monitor far-field structural marks and near-field reference marks simultaneously, enabling the far-field structural marks to be imaged clearly, enabling the near-field reference marks to be incapable of being imaged clearly because the near-field reference marks are not in a depth of field range, and enabling the near-field reference marks to be in a dispersed circle state;
(3) Establishing a camera coordinate system, an image coordinate system and a world coordinate system, calibrating a digital camera, acquiring calibration parameters, preprocessing each frame of image by using an image enhancement algorithm, and eliminating white noise and redundant information;
(4) Acquiring an initial frame image, and acquiring pixel coordinates of a near-field reference mark and a far-field structural mark in each frame image by adopting a feature detection algorithm;
(5) Acquiring a second frame image, and respectively subtracting pixel coordinates of a near-field reference mark and a far-field structural mark in the frame image from pixel coordinates of the near-field reference mark and the far-field structural mark in the initial frame to obtain displacement variation of the near-field reference mark and the far-field structural mark in a pixel coordinate system;
(6) Repeating the step (5) for the subsequent image sequence to obtain the pixel displacement values of the near-field reference mark and the far-field structure mark in the measuring process, wherein the displacement of the near-field reference mark is the camera shooting measuring error as the near-field reference mark is in a static state;
(7) The characteristic that the measurement error of the near-field reference mark is related to the measurement error of the far-field structural mark and is not related to the real displacement of the far-field structural mark is utilized, the pixel displacement of the near-field reference mark is taken as a reference signal, the pixel displacement of the far-field structural mark is taken as a basic signal, and an adaptive filter is designed to obtain the pixel displacement of the far-field structural mark after the measurement error is eliminated;
(8) And converting the pixel displacement of the far-field structural mark after the measurement error is eliminated into world displacement according to the calibration parameters, and obtaining the real displacement of the structure to be measured.
Preferably, in step (1), the stationary marker is located between the digital camera and the structure to be measured and close to the digital camera, and the stationary marker is arranged near the digital camera, so that the operation is simple.
Preferably, in the step (2), the digital camera parameter is adjusted so that the digital camera parameter monitors the far field structural mark and the near field reference mark simultaneously, the far field structural mark is clearly imaged, the near field reference mark cannot be clearly imaged because the near field reference mark is not in the depth of field range, and the far field structural mark and the near field reference mark are in a dispersed circle state.
Preferably, in the step (3), preprocessing is performed on each frame of image by using an image enhancement algorithm, wherein the preprocessing comprises the steps of firstly cutting the image, extracting a region of interest and removing an invalid region; secondly, morphological processing is carried out on the dispersed circle formed by the near-field reference mark, complex edge information in the image background is removed, the dispersed circle edge information is kept not to be destroyed, and then median filtering and binarization processing are carried out, and dispersed circle outlines are kept.
Preferably, in step (6), for each subsequent frame of image, step (5) is repeated to obtain pixel displacement values of the near field reference mark and the far field structural mark during measurement.
Preferably, in the step (7), the displacement of the near-field reference mark and the displacement of the far-field structural mark are analyzed, the measurement error represented by the displacement of the near-field reference mark is found to be related to the measurement error of the far-field structural mark, and is irrelevant to the actual displacement of the far-field structural mark, and according to the characteristic, the requirement of adaptive filtering is met, so that the pixel displacement of the near-field reference mark is taken as a reference signal, the pixel displacement of the far-field structural mark is taken as a basic signal, and the adaptive filter is designed.
Embodiments of the present invention have the following advantages:
(1) The near-field stationary reference point is easy to arrange, the problem that the far-field stationary reference point is inconvenient to find is solved, the requirement on a detected structure is low, and the universality is strong; (2) The characteristic that the far point error and the near point error have correlation is utilized to carry out precision compensation, so that the measurement accuracy is improved, and the error is small; (3) By using the automatic filtering principle, the automatic adjustment parameter can adapt to error change caused by distance measurement, thereby achieving the purpose of measuring displacement more accurately and having high accuracy.
Drawings
In order to more clearly illustrate the technical solutions of the invention or of the prior art, the drawings which are used in the description of the invention or of the prior art will be briefly described below, it being obvious that the drawings in the description below are only exemplary and that other implementation drawings can be obtained according to the extensions of the drawings provided without inventive effort for a person skilled in the art.
The structures, proportions, sizes, etc. shown in the present specification are shown only for the purposes of illustration and description, and are not intended to limit the scope of the invention, which is defined by the claims, so that any structural modifications, changes in proportions, or adjustments of sizes, which do not affect the efficacy or the objects of the invention, are deemed to fall within the ambit of the technical disclosure.
Fig. 1 is a schematic diagram of the working scenario of the present invention.
Fig. 2 is a schematic diagram of the principle of fig. 1.
Fig. 3 is an imaging schematic of the present invention.
Fig. 4 is a schematic diagram of the filter logic of the present invention.
In the figure:
1-a digital video camera; 2-quiescence markers; 3-a structure to be tested; 4-near field reference mark; 5-front depth of field; 6-post depth of field; 7-depth of field; an 8-adaptive filter; 9-base signal; 10-reference signal; 11-system output; 12-far field structural signature.
Detailed Description
Other advantages and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, by way of illustration, shows embodiments of the invention, and by way of illustration, not all embodiments, of which a person of ordinary skill in the art may attain without inventive faculty.
As shown in fig. 1 to 4, the present invention provides an image capturing measurement error suppressing method by arranging a stationary reference point in a near field, comprising the steps of:
(1) Installing a far-field structure marker 12 on a structure 3 to be tested, selecting a static field to erect a digital camera 1, arranging a static marker 2 between the digital camera 1 and the structure 3 to be tested and close to the digital camera 1, and arranging a near-field reference marker 4 on the static marker 2, wherein the near-field reference marker 4 is shown in fig. 1;
(2) Adjusting the parameters of the digital video camera 1 so that the parameters monitor the far-field structural mark 12 and the near-field reference mark 4 at the same time, and the far-field structural mark 12 is clearly imaged, wherein the near-field reference mark 4 cannot be clearly imaged because the far-field structural mark is not in the range of the depth of field 7, and is in a dispersed circle state as shown in fig. 3;
(3) And establishing a camera coordinate system, an image coordinate system and a world coordinate system, calibrating the digital camera 1, and obtaining calibration parameters. Preprocessing each frame of image by using an image enhancement algorithm to eliminate white noise and redundant information;
After the digital camera 1 is installed, a stationary marker 2 is placed in front of the digital camera 1. The digital camera 1 is used for carrying out shooting measurement on the far-field structural mark 12, the shot far-field structural mark 12 image is processed, the image plane coordinates of each calibration point are determined, the image plane coordinates on the image and the object plane coordinates on the far-field structural mark 12 are in one-to-one correspondence to form system calibration, and calibration parameters are obtained, so that the mapping relation between the two coordinates is obtained;
Preprocessing each frame of image, including image cutting, extracting a region of interest and removing an invalid region; secondly, morphological processing is carried out on the dispersed circle formed by the near-field reference mark, complex edge information in the image background is removed, and the dispersed circle edge information is kept from being destroyed; then median filtering and binarization processing are carried out, and a dispersed circle outline is reserved;
Acquiring an initial frame image, and acquiring pixel coordinates of a near-field reference mark and a far-field structural mark in each frame image by adopting a feature detection algorithm;
Taking a Hough transformation circle algorithm based on gradients as an example for a feature detection algorithm, firstly, calculating a gradient field of an image, wherein the position of a non-zero gradient vector also corresponds to the edge of the image, then, converting the gradient field into an accumulation array by utilizing a voting process, namely adding 1 vote to pixels in the non-zero gradient direction, and finally, solving the position of a local peak value in the accumulation array, namely, corresponding to the position as a circle center coordinate;
(5) Acquiring a second frame image, and respectively subtracting the pixel coordinates of the near-field reference mark 4 and the far-field structural mark 12 in the frame image from the pixel coordinates of the near-field reference mark and the far-field structural mark in the initial frame to obtain displacement variation of the near-field reference mark and the far-field structural mark in a pixel coordinate system;
(6) Repeating the step (5) for the subsequent image sequence to obtain the pixel displacement values of the near-field reference mark 4 and the far-field structural mark 12 in the measurement process, wherein the displacement of the near-field reference mark 4 is the camera measurement error because the near-field reference mark 4 is in a static state;
(7) By utilizing the characteristic that the measurement error of the near-field reference mark 4 is related to the measurement error of the far-field structural mark 12 and is not related to the real displacement of the far-field structural mark 12, the pixel displacement of the near-field reference mark 4 is used as a reference signal, the pixel displacement of the far-field structural mark 12 is used as a basic signal, and the self-adaptive filter 8 is designed, as shown in fig. 4, so that the pixel displacement of the far-field structural mark 12 after the measurement error is eliminated is obtained.
Experimental analysis shows that the measurement error of the near-field reference mark 4 is related to the measurement error of the far-field structural mark 12, but not related to the real displacement of the far-field structural mark 12, so that the precondition of using the adaptive filtering method is satisfied, and the adaptive filtering method is applied to the optimization of the photographing measurement precision; when the self-adaptive filter 8 is specifically used, the pixel coordinates of the near-field reference mark 4 are used as reference signals, the pixel coordinates of the far-field structural mark 12 are used as basic signals, the statistical characteristics of the near-field reference mark 4 and the far-field structural mark 12 are tracked, and parameters are automatically adjusted to adapt to the unknown or randomly-changed statistical characteristics of the near-field structural mark and the far-field structural mark, so that optimal filtering is realized to obtain more accurate displacement;
And converting the pixel displacement of the far-field structural mark 12 with the measurement error eliminated into world displacement according to the calibration parameters, and obtaining the real displacement of the structure to be measured.
In other embodiments, step (4) may employ other circle center of diffusion algorithms.
While the invention has been described in detail in the foregoing general description and specific examples, it will be apparent to those skilled in the art that modifications and improvements can be made thereto. Accordingly, such modifications or improvements may be made without departing from the spirit of the invention and are intended to be within the scope of the invention as claimed.
Claims (7)
1. A method of suppressing an error in image capturing measurement by disposing a near-field stationary point, comprising the steps of:
(1) Installing far-field structure marks on a structure to be tested, selecting a static field to erect a digital camera, and setting a static marker between the digital camera and the structure to be tested, wherein near-field reference marks are arranged on the static marker;
(2) Adjusting parameters of the digital camera to enable the parameters to simultaneously monitor the far field structural mark and a near field reference mark, and enable the far field structural mark to be imaged clearly, wherein the near field reference mark cannot be imaged clearly because the near field reference mark is not in a depth of field range, and is in a dispersed circle state;
(3) Establishing a camera coordinate system, an image coordinate system and a world coordinate system, calibrating the digital camera, acquiring calibration parameters, preprocessing each frame of image by using an image enhancement algorithm, and eliminating white noise and redundant information;
(4) Acquiring an initial frame image, and acquiring pixel coordinates of the near-field reference mark and the far-field structural mark in each frame image by adopting a feature detection algorithm;
(5) Acquiring a second frame image, and respectively subtracting the pixel coordinates of the near-field reference mark and the far-field structural mark in the second frame image from the pixel coordinates of the near-field reference mark and the far-field structural mark in the initial frame to obtain displacement variation of the near-field reference mark and the far-field structural mark in a pixel coordinate system;
(6) Repeating the step (5) for the subsequent image sequence until the measurement process is finished, and obtaining the pixel displacement values of the near-field reference mark and the far-field structural mark in the measurement process;
(7) Designing an adaptive filter to obtain a pixel displacement value of the far-field structural mark after the measurement error is eliminated;
(8) And converting the pixel displacement of the far-field structural mark after the measurement error is eliminated into world displacement according to the calibration parameters, and obtaining the real displacement of the structure to be measured.
2. A camera measurement error suppressing method by arranging near field stationary points according to claim 1, characterized in that: in step (1), the stationary marker is located between the digital camera and the structure to be measured near the digital camera.
3. A camera measurement error suppressing method by arranging near field stationary points according to claim 1, characterized in that: in the step (2), the far-field structural mark and the imaging of the near-field reference mark are both located on the same image.
4. A camera measurement error suppressing method by arranging near field stationary points according to claim 1, characterized in that: in step (3), the image enhancement algorithm pre-processing includes image cropping, extracting the region of interest, and removing the invalid region.
5. A camera measurement error suppressing method by arranging near field stationary points according to claim 1, characterized in that: in the step (3), eliminating white noise and redundant information comprises morphological processing of a circle of confusion formed by near-field reference marks, removing complex edge information in an image background and keeping the circle of confusion edge information undamaged, and median filtering and binarization processing and retaining the outline of the circle of confusion.
6. A camera measurement error suppressing method by arranging near field stationary points according to claim 1, characterized in that: in the step (6), the pixel displacement value of the near-field reference mark is an image capturing measurement error.
7. A camera measurement error suppressing method by arranging near field stationary points according to claim 1, characterized in that: in the step (7), the pixel displacement of the near-field reference mark is used as a reference signal, and the pixel displacement of the far-field structural mark is used as a basic signal, so as to design the self-adaptive filter.
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- 2021-06-17 CN CN202110671320.XA patent/CN113532473B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103234462A (en) * | 2013-05-08 | 2013-08-07 | 温州大学 | Measurement method for reversing shooting of structural displacement |
| CN103630072A (en) * | 2013-10-25 | 2014-03-12 | 大连理工大学 | Layout optimization method for camera in binocular vision measuring system |
| CN106289071A (en) * | 2016-08-18 | 2017-01-04 | 温州大学 | A kind of structure three-dimensional displacement monocular photographing measurement method |
| CN106441138A (en) * | 2016-10-12 | 2017-02-22 | 中南大学 | Deformation monitoring method based on vision measurement |
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