CN113532375A - Pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification - Google Patents
Pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification Download PDFInfo
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- CN113532375A CN113532375A CN202110749128.8A CN202110749128A CN113532375A CN 113532375 A CN113532375 A CN 113532375A CN 202110749128 A CN202110749128 A CN 202110749128A CN 113532375 A CN113532375 A CN 113532375A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C5/00—Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C11/00—Photogrammetry or videogrammetry, e.g. stereogrammetry; Photographic surveying
- G01C11/04—Interpretation of pictures
Abstract
The invention discloses a bridge pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification, which comprises the following steps: step 1, planning a route task; step 2, laying coding mark points; step 3, measuring coordinates of the coding mark points and recording the coordinates as a control point file; step 4, executing a route task; step 5, exporting the photos; step 6, identifying coding mark points; step 7, generating a pricking point file; step 8, importing the control point file, the photo and the pricking point file into mapping software; step 9, generating a three-dimensional point cloud; step 10, exporting point clouds; and 11, calculating the coordinates of the key points according to the point cloud. The invention combines the coding mark point identification technology with the close-range photogrammetry technology of the unmanned aerial vehicle, thereby not only expanding the application range of the industrial close-range photogrammetry technology, but also improving the result precision of the close-range photogrammetry of the unmanned aerial vehicle, so that the invention can be applied to the measurement of the key point coordinates of the bridge pier, and can protect the personal safety of measuring personnel.
Description
Technical Field
The invention relates to the technical field of engineering measurement, in particular to a bridge pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification.
Background
The highway bridge pier needs to be retested after grouting and shaping so as to ensure that the coordinates of the key points of the bridge pier are consistent with the corresponding design coordinates, and further ensure the construction quality. With present technique, survey crew need climb to pier top back and use the satellite receiver who takes a pair of king-rod to measure the pier key point. Similar measurement work has certain dangers because of the height of the highway pier between several meters and tens of meters.
The unmanned aerial vehicle close-range photogrammetry technology is widely applied to the fields of geographic mapping, three-dimensional reconstruction, engineering management and the like, and the personal safety of measuring personnel can be ensured by a non-contact measuring mode. However, the measurement accuracy of the method cannot meet the accuracy requirement of engineering measurement, so the method cannot be directly used for acquiring the coordinates of the key points of the bridge pier.
The coding mark point identification technology is generally used in the field of industrial close-range photogrammetry, and can achieve extremely high measurement accuracy due to the close shooting distance and the high image resolution. However, the technology is generally used in the indoor small-range measurement situation, and is difficult to be directly used for the measurement of the coordinates of the key points of the bridge pier.
Disclosure of Invention
The invention aims to solve the technical problem of providing a bridge pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification aiming at the defects in the prior art.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention provides a bridge pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification, which comprises the following steps:
step 1, planning a route task: planning the flight track of the unmanned aerial vehicle and the action executed at each navigation point in advance for the bridge piers to be measured by using a route planning algorithm;
and step 5, exporting the photos: after the execution of the air route task is finished, importing the photo of the unmanned aerial vehicle into a computer;
step 6, identifying coding mark points: identifying the coded mark points in each picture by using a coded mark point identification algorithm;
step 9, generating a three-dimensional point cloud: mapping software generates a three-dimensional point cloud of a pier target based on an image three-dimensional reconstruction algorithm;
step 10, point cloud derivation: exporting the point cloud obtained by calculation of mapping software into a point cloud file with a certain format for subsequent analysis and calculation;
Further, the route planning algorithm of step 1 of the present invention specifically includes:
let the point O be the center point of the top surface of the bridge pier and have the coordinate of (N)O,EO,HO) (ii) a Point P is the waypoint to be calculated with coordinates (N)P,EP,Hp) (ii) a Alpha is a horizontal included angle between the point P and the north direction, and beta is a height angle of the point P; in order to enable the image shot by the unmanned aerial vehicle to uniformly cover the bridge pier, keeping the altitude angle and the shooting distance unchanged, and planning a navigation point at fixed angles in the horizontal direction; each waypoint specifies the shooting action of the unmanned aerial vehicle by using five parameters, namely the north coordinate N of the waypointPEast coordinate EPHeight HpThe unmanned aerial vehicle course angle Yaw and the holder Pitch angle Pitch; the calculation formula is as follows:
NP＝NO+Dcosβsinα
EP＝EO+Dcosβcosα
HP＝Ho+Dsinβ
Yaw＝α+π
Pitch＝-β
d is a shooting distance, namely the distance between the unmanned aerial vehicle camera and the center point of the top surface of the pier, and is adjusted according to actual conditions; in order to improve the effect of three-dimensional reconstruction, the planning is carried out on a plurality of height angles, including 30 degrees, 45 degrees and 60 degrees; similarly, the height angle is also selected according to the actual situation.
Further, the encoding mark points in step 2 of the present invention specifically include:
the coding mark points are circular patterns, the centers of the coding mark points are black circles, the circles which are a certain distance away from the black circles at the centers are equally divided into 8 parts, white code segments represent 1, black code segments represent 0, binary sequences with the length of 8 bits can be obtained by sequentially arranging from any position, the initial points are sequentially moved and arranged, the binary sequence with the minimum value is converted into a 10-system binary sequence which is the identity number of the coding mark points, and the identity number is printed at the upper left corner of the coding mark points; the number of coded bits, the size of the coded mark points and the proportion of the concentric circles can be adjusted according to actual conditions.
Further, the method for measuring the absolute position coordinates of the center of each encoded marker in step 3 of the present invention specifically includes:
after the coding mark point is fixed on the ground, the absolute position coordinate of the center of the coding mark point is measured by using a GNSS receiver, and the selection of a coordinate system needs to be determined according to actual requirements.
Further, the algorithm for identifying the coding mark points in step 6 of the present invention specifically comprises:
reading in an unmanned aerial vehicle image;
graying the image;
gaussian filtering;
detecting edges;
contour extraction;
contour screening;
judging whether the strip of outline meets the screening condition;
if yes, carrying out ellipse fitting positioning; if not, returning to contour screening and re-screening;
projecting and transforming the coded mark points imaged as ellipses into perfect circles;
determining the radius range of the code band;
scanning a code band;
judging whether the code mark is a code mark;
if yes, decoding is carried out; if not, returning to contour screening and re-screening;
after decoding is finished, judging whether all the contours are processed;
if yes, ending the algorithm; if not, returning to the contour screening and re-screening.
Further, the specific method for performing ellipse fitting positioning in step 6 of the present invention is:
ellipse fitting positioning is to calculate the image coordinates of the center of the coding mark point, and a least square ellipse fitting algorithm is used; the equation for the ellipse is as follows:
f(x，y)＝ax2+bxy+cy2+dx+ey+f＝0
the optimal objective function for the least squares ellipse fitting is:
g(a)＝min||Da||2 s.t.4ac-b2＝1
wherein D ═ x2xy y2 xy 1]Is an n × 6 matrix, a ═ a b c d e f]TFor the optimal ellipse parameter vector, solving an optimal objective function with additional constraint to obtain the optimal ellipse parameter; the image coordinates of the center of the coding mark point are calculated by the following formula:
wherein, the image coordinate of the center of the coding mark point is (Xc, Yc); a, b, c, d, e, f correspond to the six optimal parameters of the general equation of the ellipse.
Further, the method for calculating the coordinates of the key points in step 11 of the present invention specifically includes:
1) for the point cloud of the top surface of the bridge pier after slicing, the number of the point clouds is set to be N, and the coordinate of each point is set to be (X)i，Yi，Zi) Then the elevation of the keypoint is calculated by:
wherein the content of the first and second substances,
is the elevation of the key point, N is the number of point clouds, ZiThe elevation of the ith point in the point cloud is taken as the elevation of the ith point;
2) projecting the sliced cylindrical point cloud to an XY plane, and converting the three-dimensional point cloud into a two-dimensional point cloud;
for a square cylindrical pier, dividing projected cylindrical point cloud into four parts, wherein each part belongs to one side of the cross section of the pier, performing least square line fitting on each side, and setting a linear equation as y ═ ax + b, wherein each linear has N data points, and then listing a normal equation as follows:
wherein a and b are two parameters of a straight line equation, N is the number of point clouds for fitting a straight line, (x)i，yi) The horizontal coordinate of the ith point in the point cloud is obtained;
and sequentially solving the equation of the method for each linear point cloud to obtain corresponding linear parameters, and calculating 4 intersection points of the four linear parameters to obtain the horizontal coordinates of the four angular points of the top surface of the square pier.
The invention has the following beneficial effects: according to the bridge pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification, the coding mark point identification technology and the unmanned aerial vehicle close-range photogrammetry technology are combined, so that the application range of the industrial close-range photogrammetry technology is expanded, the achievement precision of the unmanned aerial vehicle close-range photogrammetry is improved, and the method can be applied to the measurement of the bridge pier key point coordinates. The measuring personnel need not to climb the top of the pier again to measure, and the personal safety of the measuring personnel is further protected on the premise of ensuring the measuring precision. In addition, the measurement result obtained by the method is a three-dimensional model, so that richer pier information can be provided.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a diagram of the effect of airline mission planning for an embodiment of the present invention;
FIG. 2 is an example of an encoded landmark of an embodiment of the present invention;
FIG. 3 is a diagram illustrating the layout of the coding mark points according to an embodiment of the present invention;
FIG. 4 is a control point file record format according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating the recognition effect of the coding mark points according to the embodiment of the present invention;
FIG. 6 is a three-dimensional point cloud effect graph of a bridge pier generated by mapping software according to the embodiment of the invention;
FIG. 7 is a schematic diagram of calculating coordinates of key points from a three-dimensional point cloud of piers according to an embodiment of the present invention;
FIG. 8 is a general flow diagram of a method of an embodiment of the invention;
FIG. 9 is a schematic diagram of the principles and effects of a route planning algorithm according to an embodiment of the present invention;
FIG. 10 is a flow chart of the encoding landmark identifying and locating algorithm according to the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The method combines the coding mark point identification technology and the unmanned aerial vehicle close-range photogrammetry technology, and aims to ensure that the survey personnel can complete the measurement of the key points of the bridge piers on the ground on the premise of ensuring the measurement precision without climbing up the bridge piers, thereby ensuring the personal safety of the survey personnel.
The bridge pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification comprises the following steps:
planning a route task: the unmanned aerial vehicle is designed in advance by using a program, the flight track of the unmanned aerial vehicle and the action executed at each navigation point are planned, so that the coverage of the pier by the shot picture is more uniform, and the shooting efficiency is higher. Of course, the unmanned aerial vehicle can be manually operated to fly and shoot during measurement without planning in advance, but the measurement efficiency is greatly reduced. The distribution of the photographs taken using airline mission planning is shown in FIG. 1:
therefore, the pictures shot by adopting the air route task planning are uniformly and orderly arranged, a better graph condition can be formed, and the three-dimensional reconstruction work can be facilitated.
As shown in FIG. 9(a), the point O is the center point of the top surface of the pier and has the coordinate of (N)o，EO，HO) (ii) a Point P is the waypoint to be calculated with coordinates (N)P，EP，Hp) (ii) a Alpha is a horizontal included angle between the point P and the north direction, and beta is a height angle of the point P; in order to enable the image shot by the unmanned aerial vehicle to uniformly cover the bridge pier, keeping the altitude angle and the shooting distance unchanged, and planning a navigation point at fixed angles in the horizontal direction; each waypoint specifies the shooting action of the unmanned aerial vehicle by using five parameters, namely the north coordinate N of the waypointPEast coordinate EPHeight HpThe unmanned aerial vehicle course angle Yaw and the holder Pitch angle Pitch; the calculation formula is as follows:
NP＝No+Dcosβ sinα
EP＝EO+Dcosβ cosα
HP＝HO+Dsinβ
Yaw＝α+π
Pitch＝-β
wherein, D is for shooing the distance, and unmanned aerial vehicle camera is about 10m to the distance between the pier top surface central point promptly, can adjust according to actual conditions. Furthermore, to improve the effect of the three-dimensional reconstruction, the above planning can be performed at a plurality of elevation angles, such as 30 °, 45 °, 60 °, and so on. Similarly, the height angle should be selected according to the actual situation. In fig. 9(b), two elevation angles of 30 ° and 45 ° are adopted, a waypoint is planned every 15 ° in the horizontal direction, and 24 images are taken in total after the waypoint is executed, so that the bridge piers are uniformly covered. The main body of the reconstructed bridge pier model is complete, the texture is clear, and the adoption of the route planning algorithm is helpful for ensuring the subsequent three-dimensional reconstruction effect.
Laying coding mark points: in the traditional aerial photogrammetry, image control points need to be arranged on the ground for determining the attitude and position information of an image, and the image control points need to be marked in the image in a manual pricking mode during the internal data processing. The coding mark points and the image control points play the same role, and the coding mark points are adopted to facilitate automatic identification and positioning of programs and improve the automation degree of the processing flow. The coding mark points used in the invention are shown in fig. 2, and the arrangement of the coding mark points is shown in fig. 3:
the coding mark points are circular patterns, the centers of the coding mark points are black circles, the circles which are a certain distance away from the black circles at the centers are equally divided into 8 parts, white code segments represent 1, black code segments represent 0, binary sequences with the length of 8 bits can be obtained by sequentially arranging from any position, the initial points are sequentially moved and arranged, the binary sequence with the minimum value is converted into a 10-system binary sequence which is the identity number of the coding mark points, and the identity number is printed at the upper left corner of the coding mark points; the number of coded bits, the size of the coded mark points and the proportion of the concentric circles can be adjusted according to actual conditions. The identity number shown in the embodiment of the present invention is 21, and this identity number is merely an example.
Measuring coordinates of the coding mark points and recording the coordinates as a control point file: after the code mark points are laid, the absolute position coordinates of the centers of the code mark points need to be measured, and the coordinate system of the absolute position coordinates is consistent with the coordinate system of the key point coordinates of the bridge pier. Each coding mark point has a unique identity number, and each identity number and the corresponding coordinate information are stored in a control point file as a record. The recording format is shown in fig. 4.
The coding mark point is used as an image control point in the invention, so that after the coding mark point is fixed on the ground, a GNSS receiver is needed to measure the absolute position coordinates of the center of the coding mark point, and the selection of a coordinate system needs to be determined according to the actual requirement. GNSS is called Global Navigation Satellite System, i.e. Global Navigation Satellite System. GNSS receivers perform positioning and measurements by receiving multiple navigation satellite signals.
And (3) executing the air route task: and enabling the unmanned aerial vehicle to fly according to the planned air route in advance and take pictures.
And (3) exporting the photos: and after the execution of the air route task is finished, the photo of the unmanned aerial vehicle is led into the computer from the memory card of the unmanned aerial vehicle.
And (3) identification of coding mark points: and identifying the coded mark points in each picture by using a coded mark point identification algorithm. The recognition effect is shown in fig. 5.
The coding mark point identification algorithm specifically comprises the following steps:
reading in an unmanned aerial vehicle image;
graying the image;
gaussian filtering;
detecting edges;
contour extraction;
contour screening;
judging whether the strip of outline meets the screening condition;
if yes, carrying out ellipse fitting positioning; if not, returning to contour screening and re-screening;
projecting and transforming the coded mark points imaged as ellipses into perfect circles;
determining the radius range of the code band;
scanning a code band;
judging whether the mark points are coding mark points or not;
if yes, decoding is carried out; if not, returning to contour screening and re-screening;
after decoding is finished, judging whether all the contours are processed;
if yes, ending the algorithm; if not, returning to the contour screening and re-screening.
The specific method for carrying out ellipse fitting positioning comprises the following steps:
ellipse fitting positioning is to calculate the image coordinates of the center of the coding mark point, and a least square ellipse fitting algorithm is used; the equation for the ellipse is as follows:
f(x，y)＝ax2+bxy+cy2+dx+ey+f＝0
the optimal objective function for the least squares ellipse fitting is:
g(a)＝min||Da||2 s.t.4ac-b2＝1
wherein D ═ x2xy y2 x y 1]Is an n × 6 matrix, a ═ a b cd e f]TFor the optimal ellipse parameter vector, solving an optimal objective function with additional constraint to obtain the optimal ellipse parameter; the image coordinates of the center of the coding mark point are calculated by the following formula:
wherein, the image coordinate of the center of the coding mark point is (Xc, Yc); a, b, c, d, e, f correspond to the six optimal parameters of the general equation of the ellipse.
And (3) generating a pricking point file: the coded mark point identification algorithm can identify the identity number of the coded mark point, can calculate the image coordinate of the central point of the coded mark point, and stores the image coordinate of each coded mark point in each image as a text file, namely a pricking point file.
Importing the control point file, the photo and the pricking point file into mapping software: these three files are data indispensable for photogrammetry, and therefore, all of them are imported into the mapping software.
Generating a three-dimensional point cloud: the mapping software generates a three-dimensional point cloud of the pier target based on an image three-dimensional reconstruction algorithm. The process comprises three steps of air-to-three encryption, pose optimization and dense matching. The generated three-dimensional point cloud is shown in fig. 6:
and (3) point cloud derivation: and exporting the point cloud obtained by calculation of the mapping software into a point cloud file with a certain format for subsequent analysis and calculation.
Calculating key point coordinates according to the point cloud: the calculation method used will be different according to the key points to be calculated. For example: for a square pier, the key points are four angular points of the top surface of the pier, so that a cylindrical point cloud at the top of the pier can be sliced (as shown in fig. 7a), a linear equation of four sides is calculated by adopting a linear fitting mode, and further horizontal coordinates of the four angular points are calculated (as shown in fig. 7 b); and (4) calculating the average value of the point cloud heights of the pier top surface point cloud slices (shown in FIG. 7c) as the elevation coordinates of four corner points (shown in FIG. 7 d).
1) For the point cloud of the top surface of the bridge pier after slicing, the number of the point clouds is set to be N, and the coordinate of each point is set to be (X)i，Yi，Zi) Then the elevation of the keypoint is calculated by:
wherein the content of the first and second substances,
is the elevation of the key point, N is the number of point clouds, ZiThe elevation of the ith point in the point cloud is taken as the elevation of the ith point;
2) projecting the sliced cylindrical point cloud to an XY plane, and converting the three-dimensional point cloud into a two-dimensional point cloud;
for a square cylindrical pier, dividing projected cylindrical point cloud into four parts, wherein each part belongs to one side of the cross section of the pier, performing least square line fitting on each side, and setting a linear equation as y ═ ax + b, wherein each linear has N data points, and then listing a normal equation as follows:
wherein a and b are two parameters of a straight line equation, N is the number of point clouds for fitting a straight line, (x)i，yi) The horizontal coordinate of the ith point in the point cloud is obtained;
and sequentially solving the equation of the method for each linear point cloud to obtain corresponding linear parameters, and calculating 4 intersection points of the four linear parameters to obtain the horizontal coordinates of the four angular points of the top surface of the square pier.
In conclusion, the invention combines the coding mark point identification technology and the unmanned aerial vehicle close-range photogrammetry technology, can ensure that the measuring personnel can complete the measurement of the key points on the top surface of the bridge pier without climbing up the bridge pier, ensures the personal safety of the measuring personnel to a certain extent, and can provide richer measurement results compared with the traditional measurement mode.
In another embodiment of the invention:
and planning a course task in advance according to the design coordinates of the bridge piers by using a course planning program. A certain number (at least 3) of coding mark points with different pairwise are selected, a material with a rough surface (such as non-woven fabric or canvas) is used for printing, and the printing size is changed according to the height of a pier and the difference of an unmanned aerial vehicle camera. Taking an unmanned aerial vehicle of Dajiang eidolon 4RTK model as an example, the size of the coding mark point is recommended to be more than 0.3m multiplied by 0.3m for a bridge pier with the height of about 10 m. The higher the pier is, the higher the flying height of the unmanned aerial vehicle is, the lower the ground resolution of the image is, and the size of the coding mark point should be increased correspondingly.
When in field measurement, the coding mark points are arranged around the bridge pier and fixed, and the horizontal distribution of the coding mark points can preferably surround the bridge pier. And then measuring the three-dimensional coordinates of the center of the coding mark point, and sorting the measured coordinates into a control point file. And then calling a planned flight path task file in advance, so that the unmanned aerial vehicle takes off and takes a certain number of pictures around the bridge pier according to the flight path task. And after the airline task is finished, the unmanned aerial vehicle is landed, and the shot picture is led into the computer.
And (3) identifying each coding mark point in each picture by using a coding mark point identification program, calculating the image coordinates of each coding mark point, and generating a pricking point file. The method comprises the steps of importing a control point file, a photo and a puncture point file into mapping software (the mapping software has many types, such as Metascape, ContextCapture, Pix4d and the like, the invention is not limited, but the Metascape software is recommended to be used), calculating to obtain three-dimensional point cloud of the bridge pier, and exporting the three-dimensional point cloud into a point cloud file with a certain format. And calculating the derived point cloud by adopting a corresponding method according to the type of the key point to be measured, so as to obtain the three-dimensional coordinates of the key point.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (7)
1. A pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification is characterized by comprising the following steps:
step 1, planning a route task: planning the flight track of the unmanned aerial vehicle and the action executed at each navigation point in advance for the bridge piers to be measured by using a route planning algorithm;
step 2, laying coding mark points: arranging a plurality of coding mark points around the bridge pier;
step 3, measuring coordinates of the coding mark points and recording the coordinates as a control point file: measuring the absolute position coordinates of the centers of the coding mark points, wherein the coordinate system of the absolute position coordinates is consistent with the coordinate system of the key points of the bridge piers; setting a unique identity number for each coding mark point, and storing each identity number and the corresponding coordinate information as a record in a control point file;
step 4, executing the air route task: enabling the unmanned aerial vehicle to fly according to a planned air route in advance and taking a picture;
and step 5, exporting the photos: after the execution of the air route task is finished, importing the photo of the unmanned aerial vehicle into a computer;
step 6, identifying coding mark points: identifying the coded mark points in each picture by using a coded mark point identification algorithm;
step 7, generating a pricking point file: identifying the identity number of the coding mark point through a coding mark point identification algorithm, calculating the image coordinate of the central point of the coding mark point, and storing the image coordinate of each coding mark point in each picture as a text file, namely a pricking point file;
step 8, importing the control point file, the photo and the pricking point file into mapping software;
step 9, generating a three-dimensional point cloud: mapping software generates a three-dimensional point cloud of a pier target based on an image three-dimensional reconstruction algorithm;
step 10, point cloud derivation: exporting the point cloud obtained by calculation of mapping software into a point cloud file with a certain format for subsequent analysis and calculation;
step 11, calculating key point coordinates according to the point cloud: slicing the cylindrical point cloud at the top of the pier, calculating linear equations of four sides in a linear fitting mode, and further calculating horizontal coordinates of four angular points; and slicing the point cloud on the top surface of the pier, and calculating the average value of the height of the point cloud as the elevation coordinates of four angular points.
2. The pier key point measuring method based on unmanned aerial vehicle measurement and coded mark point identification according to claim 1, wherein the route planning algorithm of step 1 is specifically:
let the point O be the center point of the top surface of the bridge pier and have the coordinate of (N)O,EO,HO) (ii) a Point P is the waypoint to be calculated with coordinates (N)P,EP,Hp) (ii) a Alpha is a horizontal included angle between the point P and the north direction, and beta is a height angle of the point P; in order to enable the image shot by the unmanned aerial vehicle to uniformly cover the bridge pier, keeping the altitude angle and the shooting distance unchanged, and planning a navigation point at fixed angles in the horizontal direction; each waypoint specifies the shooting action of the unmanned aerial vehicle by using five parameters, namely the north coordinate N of the waypointPEast coordinate EPHeight HpThe unmanned aerial vehicle course angle Yaw and the holder Pitch angle Pitch; the calculation formula is as follows:
NP＝NO+Dcosβsinα
EP＝EO+Dcosβcosα
HP＝HO+Dsinβ
Yaw＝α+π
Pitch＝-β
d is a shooting distance, namely the distance between the unmanned aerial vehicle camera and the center point of the top surface of the pier, and is adjusted according to actual conditions; in order to improve the effect of three-dimensional reconstruction, the planning is carried out on a plurality of height angles, including 30 degrees, 45 degrees and 60 degrees; similarly, the height angle is also selected according to the actual situation.
3. The pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification according to claim 1, wherein the coding mark points in the step 2 are specifically:
the coding mark points are circular patterns, the centers of the coding mark points are black circles, the circles which are a certain distance away from the black circles at the centers are equally divided into 8 parts, white code segments represent 1, black code segments represent 0, binary sequences with the length of 8 bits can be obtained by sequentially arranging from any position, the initial points are sequentially moved and arranged, the binary sequence with the minimum value is converted into a 10-system binary sequence which is the identity number of the coding mark points, and the identity number is printed at the upper left corner of the coding mark points; the number of coded bits, the size of the coded mark points and the proportion of the concentric circles can be adjusted according to actual conditions.
4. The bridge pier key point measuring method based on unmanned aerial vehicle measurement and coded mark point identification as claimed in claim 1, wherein the method for measuring the absolute position coordinates of the centers of the coded mark points in step 3 specifically comprises:
after the coding mark point is fixed on the ground, the absolute position coordinate of the center of the coding mark point is measured by using a GNSS receiver, and the selection of a coordinate system needs to be determined according to actual requirements.
5. The pier key point measuring method based on unmanned aerial vehicle measurement and coding mark point identification according to claim 1, wherein the coding mark point identification algorithm in the step 6 is specifically:
reading in an unmanned aerial vehicle image;
graying the image;
gaussian filtering;
detecting edges;
contour extraction;
contour screening;
judging whether the strip of outline meets the screening condition;
if yes, carrying out ellipse fitting positioning; if not, returning to contour screening and re-screening;
projecting and transforming the coded mark points imaged as ellipses into perfect circles;
determining the radius range of the code band;
scanning a code band;
judging whether the mark points are coding mark points or not;
if yes, decoding is carried out; if not, returning to contour screening and re-screening;
after decoding is finished, judging whether all the contours are processed;
if yes, ending the algorithm; if not, returning to the contour screening and re-screening.
6. The pier key point measuring method based on unmanned aerial vehicle measurement and coded mark point identification as claimed in claim 1, wherein the specific method for performing ellipse fitting positioning in step 6 is:
ellipse fitting positioning is to calculate the image coordinates of the center of the coding mark point, and a least square ellipse fitting algorithm is used; the equation for the ellipse is as follows:
f(x,y)＝ax2+bxy+cy2+dx+ey+f＝0
the optimal objective function for the least squares ellipse fitting is:
g(a)＝min||Da||2s.t.4ac-b2＝1
wherein D ═ x2 xy y2 x y 1]Is an n × 6 matrix, a ═ a b c d e f]TFor the optimal ellipse parameter vector, solving an optimal objective function with additional constraint to obtain the optimal ellipse parameter; the image coordinates of the center of the coding mark point are calculated by the following formula:
wherein, the image coordinate of the center of the coding mark point is (Xc, Yc); a, b, c, d, e, f correspond to the six optimal parameters of the general equation of the ellipse.
7. The bridge pier key point measuring method based on unmanned aerial vehicle measurement and coded mark point identification as claimed in claim 1, wherein the method for calculating key point coordinates in step 11 specifically comprises:
1) for the point cloud of the top surface of the bridge pier after slicing, the number of the point clouds is set to be N, and the coordinate of each point is set to be (X)i,Yi,Zi) Then the elevation of the keypoint is calculated by:
wherein the content of the first and second substances,
is the elevation of the key point, N is the number of point clouds, ZiThe elevation of the ith point in the point cloud is taken as the elevation of the ith point;
2) projecting the sliced cylindrical point cloud to an XY plane, and converting the three-dimensional point cloud into a two-dimensional point cloud;
for a square cylindrical pier, dividing projected cylindrical point cloud into four parts, wherein each part belongs to one side of the cross section of the pier, performing least square line fitting on each side, and setting a linear equation as y ═ ax + b, wherein each linear has N data points, and then listing a normal equation as follows:
wherein a and b are two parameters of a straight line equation, N is the number of point clouds for fitting a straight line, (x)i,yi) The horizontal coordinate of the ith point in the point cloud is obtained;
and sequentially solving the equation of the method for each linear point cloud to obtain corresponding linear parameters, and calculating 4 intersection points of the four linear parameters to obtain the horizontal coordinates of the four angular points of the top surface of the square pier.
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