CN114638095A - Photogrammetric precision simulation method for large-scale mesh antenna reflector - Google Patents

Photogrammetric precision simulation method for large-scale mesh antenna reflector Download PDF

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CN114638095A
CN114638095A CN202210225932.0A CN202210225932A CN114638095A CN 114638095 A CN114638095 A CN 114638095A CN 202210225932 A CN202210225932 A CN 202210225932A CN 114638095 A CN114638095 A CN 114638095A
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deviation
image point
reflector
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王河伟
郭廷钧
李立峰
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Zhengzhou Sunward Technology Co ltd
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Abstract

The invention provides a photogrammetry precision simulation method for a large-scale mesh antenna reflector, which belongs to the technical field of photogrammetry. The whole precision simulation process of the invention does not need to actually measure the reflector real object, only considers the measurement error of the photogrammetry, and can estimate the measurement precision of the reflector in the design stage of the reflector; the simulation result of the invention not only contains the model measurement accuracy statistic value of the reflector, but also contains the deviation distribution of each point, thus providing a foundation for optimizing the measurement network model.

Description

Photogrammetric precision simulation method for large-scale mesh antenna reflector
Technical Field
The invention relates to the technical field of photogrammetry, in particular to a photogrammetry precision simulation method for a large-scale mesh antenna reflector.
Background
The photogrammetry is the main method for measuring the profile of the existing large-scale mesh antenna reflector, a single camera or a plurality of cameras shoot the profile of the reflector to obtain a measurement image of a mark point on the reflector, the three-dimensional point coordinates of the mark are obtained by algorithms and technical means such as subsequent image processing, mark center positioning, station setting splicing, three-dimensional point intersection, adjustment of a light beam method and the like, and finally the measurement deviation of the profile is obtained by fitting and comparing the three-dimensional point and a reflector design model.
The measurement accuracy of the existing reflector is generally evaluated by actually measuring measurement points on a molded surface of the reflector and then performing point-to-design model best fitting to obtain RMS of fitting deviation as a standard for measuring accuracy evaluation. The accuracy of the profile measurement is typically estimated for reflectors that are in the design or are otherwise not in physical condition, typically by the nominal accuracy of the measurement device. The following problems exist in the several methods for estimating and evaluating the accuracy of the reflector:
1) the method of evaluating the measurement accuracy of a reflector by best-fitting a point on the actual measurement reflector to a model mixes the manufacturing variation of the reflector itself with the measurement variation of the photogrammetry itself, and theoretically cannot be used as a measurement error evaluation value for evaluating the photogrammetry itself.
2) The nominal accuracy of the measuring equipment can be achieved under good measuring conditions, and the scenes and the distribution of the stations measured by the actual reflectors are not necessarily ideal and cannot necessarily achieve the nominal accuracy of the measuring equipment. And the nominal accuracy of the measuring device is directed to the three-dimensional coordinates of the measuring point and not directly to the reflector profile. This method is also inaccurate and unreliable.
Therefore, it is desirable to provide a simulation method for photogrammetry accuracy of large mesh antenna reflectors to solve the above existing problems.
Disclosure of Invention
In view of the above, the invention provides a simulation method for photogrammetry precision of a large-scale mesh antenna reflector, which is characterized in that the distribution characteristics of image point measurement deviation are statistically analyzed, a random generation model of the image point measurement deviation is established according to a Monte Carlo simulation method, the designed shooting position and measurement point distribution are combined, and the combined shooting position and measurement point distribution are input into a combined mathematical model of photogrammetry and point model fitting measurement to perform multiple simulation calculations to obtain the final measurement precision estimation of the antenna reflector.
In order to solve the existing technical problems, the invention provides a photogrammetric precision simulation method of a large-scale mesh antenna reflector, which comprises the following steps:
step 1, counting the image point deviation of a measuring camera during distortion calibration, and counting the average value Avgx and the standard deviation StdPx of the image point deviation distribution characteristic in the x direction and the average value Avgy and the standard deviation StdPy in the y direction;
step 2, generating a random image point deviation in normal distribution according to the average value and the standard deviation of the image point deviation in the step 1;
step 3, generating non-deviation image point coordinates corresponding to each camera station according to the collinear condition equation according to the designed camera station position posture and the three-dimensional coordinates of the mark points;
step 4, generating simulated image point coordinate values by adding the non-deviation image point coordinates generated in the step 3 and the random deviation amount normally distributed in the step 2, and inputting the combined designed camera station position posture and the mark three-dimensional point coordinates into a beam adjustment model for resolving to obtain simulated mark three-dimensional point coordinate values;
step 5, performing point-to-model fitting on the simulated three-dimensional point coordinate value generated in the step 4 and the antenna reflector design model to obtain the simulation measurement precision of the reflector profile;
and 6, repeating the steps 4 to 5 for 100 times to obtain the simulation measurement precision.
Further, in step 2, a random number sequence follows a one-dimensional normal distribution, and then has the following probability density function:
Figure BDA0003535669650000021
where μ, σ >0 and are constants that are mathematical expectation and mean square error, respectively; the average value of the image point deviation is approximate to the mathematical expectation, the standard deviation approximate variance of the image point deviation is introduced into the probability density function, and the image point deviation random number conforming to the normal distribution is generated.
Further, the collinearity condition equation in step 3 is:
Figure BDA0003535669650000022
Figure BDA0003535669650000023
in the formula:
x and y are coordinates of image points;
x0，y0f is an internal orientation element of the image;
XS，YS，ZSis the location of the camera station;
XA，YA，ZAthree-dimensional coordinates of object space points;
ai，bi，ci(i ═ 1, 2, 3) are the 9 direction cosines of the 3 exterior orientation angle elements of the rover.
Furthermore, the bundle adjustment in step 4 is implemented by using a bundle of light rays composed of an image as a basic unit of adjustment, using a collinear equation of central projection as a basic equation of adjustment, and by rotation and translation of each bundle of light rays in space, intersection of light rays at a common point between models is implemented.
Further, in the step 6, the steps 4 to 5 are repeated for 100 times, and the root mean square, the maximum value and the minimum value of the profile simulation deviation are taken as the characteristic values for evaluating the reflector profile simulation accuracy.
The technical scheme of the invention at least comprises the following beneficial effects:
1. in the whole precision simulation process, the reflector real object does not need to be actually measured, and only the measurement error of the photogrammetry is considered, so that the measurement precision of the reflector can be estimated in the design stage of the reflector;
2. in the whole simulation estimation process, a large number of image point deviation samples are used as a reference for carrying out multiple times of simulation, so that the precision and the reliability are ensured;
3. the simulation result of the invention not only contains the model measurement accuracy statistic of the reflector, but also contains the deviation distribution of each point, thus providing a foundation for optimizing the measurement net model;
4. the whole simulation process is completely finished on a computer, manual field data acquisition is not involved, labor cost is saved, and efficiency is improved.
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FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic diagram of light velocity method adjustment according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of non-biased pixel coordinates according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of simulated three-dimensional point coordinates in an embodiment of the invention;
FIG. 5 is a diagram of the measurement results from a simulation of three-dimensional points to a model in an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to fig. 1 to 5 of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.
A photogrammetric measurement precision simulation method for a large mesh antenna reflector comprises the following steps:
step 1, counting the image point deviation of a measuring camera during distortion calibration, and counting the average value Avgx and the standard deviation StdPx of the image point deviation distribution characteristic in the x direction and the average value Avgy and the standard deviation StdPy in the y direction;
step 2, generating a random image point deviation in normal distribution according to the average value and the standard deviation of the image point deviation in the step 1; given that the method for generating random numbers for the distribution of probability density functions is called an arbitrary distribution method for generating random numbers for the example of a typical normal distribution, if a random number sequence follows a one-dimensional normal distribution, it has the following probability density function:
Figure BDA0003535669650000041
where μ, σ >0 and are constants that are mathematical expectation and mean square error, respectively; the average value of the image point deviation is approximate to the mathematical expectation, the standard deviation approximate variance of the image point deviation is introduced into the probability density function, and the image point deviation random number conforming to the normal distribution is generated.
Step 3, generating non-deviation image point coordinates corresponding to each camera station according to the collinear condition equation according to the designed camera station position posture and the three-dimensional coordinates of the mark points; the collinearity condition equation is:
Figure BDA0003535669650000042
Figure BDA0003535669650000043
in the formula:
x and y are coordinates of image points;
x0，y0f is an internal orientation element of the image;
XS，YS，ZSis the location of the camera station;
XA，YA，ZAthree-dimensional coordinates of object space points;
ai，bi，ci(i-1, 2, 3) is composed of 3 external orientation angle elements of a camera station9 direction cosines.
Step 4, generating simulated image point coordinate values by adding the non-deviation image point coordinates generated in the step 3 and the random deviation amount normally distributed in the step 2, and inputting the combined designed camera station position posture and the mark three-dimensional point coordinates into a beam adjustment model for resolving to obtain simulated mark three-dimensional point coordinate values; the bundle adjustment is that a bundle of light rays composed of an image is used as a basic unit of the adjustment, a collinear equation of central projection is used as a basic equation of the adjustment, and the light rays of a common point between models realize the optimal intersection through the rotation and translation of each light ray bundle in space.
And 5, performing point-to-model fitting on the simulated three-dimensional point coordinate value generated in the step 4 and the antenna reflector design model to obtain the simulation measurement precision of the reflector profile.
And 6, repeating the steps four to five for 100 times to obtain the simulation measurement precision.
One embodiment of the invention is a simulation of the photogrammetric precision of a large mesh antenna reflector (with the caliber of 20 meters) profile in a certain space unit, and the test method comprises the following steps:
1. and (5) counting the statistical characteristics, the average value and the standard deviation of the image point residual error when the camera is calibrated, wherein the statistical results are shown in the table below.
Figure BDA0003535669650000051
2. MPS industrial photogrammetry software of Chen-dimension science and technology is used for importing the position posture of a designed camera station and the three-dimensional coordinates of a mark point to calculate the corresponding non-deviation image point coordinates, as shown in figure 3.
3. The computed unbiased image point coordinates are added with the normally distributed random errors, and the unbiased image point coordinates are brought into MPS industrial photogrammetry software to perform bundle adjustment by combining the input designed camera station position posture and the three-dimensional point coordinates, so as to obtain simulated three-dimensional point coordinates, as shown in FIG. 4.
4. And (3) obtaining a three-dimensional coordinate and a reflector design model according to simulation, and performing point-to-model best fitting to obtain a simulated reflector profile measurement result, as shown in fig. 5.
5. And repeating the steps 4-5 for 100 times, and taking the root mean square (0.32mm), the maximum value (0.7mm) and the minimum value (-1.3mm) of the profile simulation deviation as characterization values for evaluating the simulation precision of the reflector profile.
The method illustrated by this example has the following advantages:
1) the simulation result is reliable: if the nominal 4um +4um/m measurement precision is measured according to MPS industrial photogrammetry, the profile measurement precision estimation value is 0.084 mm, the root mean square of deviation from an antenna actual measurement point to a simulation best fit is 1.58mm, and the repeatability of actual multi-measurement profile deviation RMS is 0.29mm, so the profile deviation result (0.32mm) estimated by the method is closer to the measurement precision of the actual photogrammetry system for measuring the reflector profile.
2) The simulation result of the method not only comprises the antenna profile measurement estimation value, but also comprises the maximum deviation, the minimum deviation and the deviation distribution diagram, the result is richer, and the further analysis is facilitated.
The foregoing is a preferred embodiment of the present invention, and it should be noted that it would be apparent to those skilled in the art that various modifications and enhancements can be made without departing from the principles of the invention, and such modifications and enhancements are also considered to be within the scope of the invention.

Claims (5)

1. A photogrammetry precision simulation method for a large-scale mesh antenna reflector is characterized by comprising the following steps:
step 1, counting the image point deviation of a measuring camera during distortion calibration, and counting the average value Avgx and the standard deviation StdPx of the image point deviation distribution characteristic in the x direction and the average value Avgy and the standard deviation StdPy in the y direction;
step 2, generating a random image point deviation in normal distribution according to the average value and the standard deviation of the image point deviation in the step 1;
step 3, generating non-deviation image point coordinates corresponding to each camera station according to the collinear condition equation according to the designed camera station position posture and the three-dimensional coordinates of the mark points;
step 4, generating simulated image point coordinate values by adding the non-deviation image point coordinates generated in the step 3 and the random deviation amount normally distributed in the step 2, and inputting the combined designed camera station position posture and the mark three-dimensional point coordinates into a beam adjustment model for resolving to obtain simulated mark three-dimensional point coordinate values;
step 5, performing point-to-model fitting on the simulated three-dimensional point coordinate value generated in the step 4 and the antenna reflector design model to obtain the simulation measurement precision of the reflector profile;
and 6, repeating the steps 4 to 5 for 100 times to obtain the simulation measurement precision.
2. The method as claimed in claim 1, wherein in step 2, a random number sequence follows a one-dimensional normal distribution, and has a probability density function as follows:
Figure FDA0003535669640000011
where μ, σ >0 and are constants that are mathematical expectation and mean square error, respectively; the average value of the image point deviation is approximate to the mathematical expectation, the standard deviation approximate variance of the image point deviation is introduced into the probability density function, and the image point deviation random number conforming to the normal distribution is generated.
3. The simulation method for photogrammetry precision of large mesh antenna reflector according to claim 1, wherein the collinear condition equation in step 3 is as follows:
Figure FDA0003535669640000012
Figure FDA0003535669640000013
in the formula:
x and y are coordinates of image points;
x0，y0f is an internal orientation element of the image;
XS，YS，ZSis the location of the camera station;
XA，YA，ZAthree-dimensional coordinates of object space points;
ai，bi，ci(i ═ 1, 2, 3) are the 9 direction cosines of the 3 exterior orientation angle elements of the camera.
4. The simulation method for photogrammetry precision of large mesh antenna reflector according to claim 1, wherein the bundle adjustment in step 4 is implemented by using a bundle of rays composed of an image as a basic unit of adjustment, using a collinear equation of central projection as a basic equation of adjustment, and using rotation and translation of each bundle of rays in space to realize intersection of rays at a common point between models.
5. The method for simulating photogrammetric accuracy of the large mesh antenna reflector according to claim 1, wherein in the step 6, the steps 4-5 are repeated 100 times, and the root mean square, the maximum value and the minimum value of the profile simulation deviation are taken as characteristic values for evaluating the reflector profile simulation accuracy.
CN202210225932.0A 2022-03-07 2022-03-07 Photogrammetric precision simulation method for large-scale mesh antenna reflector Pending CN114638095A (en)

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