A raw particle image stitching method for large field of view PIV measurement

Abstract

The application discloses a raw particle image splicing method for large-view-field PIV measurement, and steps include: estimating a camera lens focal length, installing a system camera, selecting a calibration plate and adjusting a camera posture, shooting a calibration plate image, determining a world coordinate system and positioning multi-camera images based on a common area of the calibration plate, performing a PIV test, and completing multi-camera raw tracer particle large-view-field image splicing; the method shoots raw tracer particle images through two or more PIV system cameras, uses the calibration plate as an image splicing medium, and splices two or more PIV raw tracer particle images into one large-view-field PIV raw tracer particle image; the splicing method realizes image splicing of raw tracer particle images in a multi-camera 2D2C PIV measurement test, and improves test quality.

Description

Technical Field

[0001] This invention relates to the field of aerodynamic testing, and more specifically to a method for stitching raw particle images for large field-of-view (PIV) measurements. Background Technology

[0002] PIV (Positive Infrared) technology is a promising non-contact optical spatial flow velocity field measurement technique. It features low or no interference with the flow field and high spatial resolution, making it one of the most important methods for measuring spatial flow field characteristic parameters. It is widely used in various fluid mechanics experiments and has played a crucial role in the development of fluid mechanics theory and the research and development of various ground transportation vehicles, ships, and aircraft. With the rapid advancements in next-generation materials technology, laser technology, imaging technology, and image processing technology, as well as the emergence of new theories, PIV technology has also experienced rapid development, moving towards larger field of view, higher precision, higher spatiotemporal resolution, and volumetric spatial measurement and particle tracking.

[0003] Large field-of-view spatial flow velocity field measurement is one of the development directions of PIV technology. Through large field-of-view flow field measurement, it is possible to observe and grasp the large-scale structure of fluid flow, understand specific flow phenomena from a macroscopic perspective, and analyze and diagnose fluid flow as a whole, discover specific aerodynamic phenomena, and study aerodynamic mechanisms.

[0004] When conducting large field-of-view (2D2C) spatial velocity field measurements, to ensure the measurement data has a certain spatial resolution, a single camera is usually insufficient to meet the spatial resolution requirements, such as a spatial resolution better than 1 mm / pixel. In this case, two or more cameras are needed to simultaneously capture tracer particle images of the measurement area, and then the images are stitched together to form large field-of-view PIV experimental data. A common approach is to use the raw tracer particle images captured separately by each camera to calculate the spatial velocity field vector image data, and then stitch the obtained spatial velocity field vector images together to form large field-of-view PIV experimental data (referred to as post-stitching). This post-stitching method results in significant data discontinuities in the stitched area, affecting the quality of the experimental data. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method for stitching original particle images for large field-of-view PIV measurements. This method enables the stitching of original tracer particle images during multi-camera 2D2C (2 Dimensional 2 Component) PIV measurement experiments, effectively resolving the problem of discontinuous velocity vectors in the stitching region of PIV velocity field data.

[0006] To achieve the above-mentioned objectives, the present invention employs the following technical solution: a method for stitching raw particle images for large field-of-view (PIV) measurements, comprising the following steps:

[0007] Step 1: Based on the size of the area to be measured: a The long side of the plane of the region to be measured, b The short side of the plane of the area to be measured; the imaging chip specifications of the first and second cameras of the PIV system: m For the long side of the imaging chip specification, n The short side of the imaging chip, the proposed camera mounting location, and its distance from the plane of the measurement area are defined. s Preliminary calculation of the focal length of the PIV camera lens f ;

[0008] Step 2: Depending on the specific conditions of the PIV measurement area, install the two cameras of the PIV system in appropriate positions, either horizontally or vertically.

[0009] Step 3: Select the calibration plate and place it within the field of view of the first camera of the PIV system. The size of the short side of the calibration plate should not be less than 1 / 2 of the short side of the field of view of the first camera. Move the calibration plate within the plane of the area to be measured and adjust the position and orientation of the first camera so that the field of view of the first camera covers one end of the plane of the area to be measured.

[0010] Step 4: Move the calibration plate within the plane of the area to be measured so that it is in the overlapping area of ​​the shooting areas of the first camera and the second camera. Adjust the position of the second camera so that the field of view of the second camera covers the remaining area of ​​the plane of the measurement area, and make the overlapping area of ​​the images of the first camera and the second camera not less than 1 / 10 of the camera's field of view.

[0011] Step 5: Move the calibration board in the overlapping area of ​​the two camera images, and control the first camera and the second camera to simultaneously capture no less than 10 sets of calibration board images. Move the calibration board in the plane of the measurement area so that it is within the field of view of the first camera or the second camera, and control the first camera or the second camera to capture no less than 10 sets of calibration board images.

[0012] Step 6: Establish a world coordinate system based on the image captured by the first camera. Based on the marker points of the common part of the calibration plate in the images of the first and second cameras, and the world coordinate system established based on the image captured by the first camera, accurately place the image captured by the second camera in the world coordinate system by moving and scaling, that is, determine the position of the image captured by the first camera in the world coordinate system.

[0013] Step 7: Conduct a formal PIV test;

[0014] Step 8: Based on the position of the image captured by the second camera in the world coordinate system obtained in Step 6, remove the overlapping area in the image captured by the second camera, and place it into the world coordinate system containing the image captured by the second camera formed by the image captured by the first camera, to form the original large field-of-view image of the tracer particles in the PIV experiment.

[0015] The advantages and beneficial effects of this invention are as follows: by using the large field-of-view images of the original tracer particles formed by multiple cameras based on pre-stitching technology for subsequent PIV velocity field calculation, the problem of data discontinuity in the post-stitched data is effectively solved, and the image stitching of the original tracer particle images in the multi-camera 2D2C PIV measurement experiment is realized, thereby improving the quality of the experimental data. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a method for stitching raw tracer particle images for multi-camera large field-of-view PIV measurements according to the present invention.

[0017] In the figure: 1-First camera 1, 2-Second camera 2, 3-Calibration plate, 4-Field of view of the first camera, 5-Field of view of the second camera, 6-Planar of the area to be measured, 7-Image overlap area. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to the overview and accompanying drawings.

[0019] Example

[0020] like Figure 1 As shown, a method for stitching raw particle images for large field-of-view (PIV) measurements includes the following steps:

[0021] Step 1: Based on the size of the area to be measured, plane 6: a is the long side of the area to be measured, b is the short side of the area to be measured, the imaging chip specifications of the first camera 1 and the second camera 2 of the PIV system: m is the long side of the imaging chip specification, n is the short side of the imaging chip specification, the proposed installation position of the camera and its distance from the measurement area, plane 6. s Preliminary calculation of the focal length of the PIV camera lens f ;

[0022] Step 2: Depending on the specific conditions of plane 6 of the PIV measurement area, install the two cameras of the PIV system in appropriate positions, either horizontally or vertically.

[0023] Step 3: Select a calibration plate and place it within the field of view of the first camera 1 of the PIV system. The size of the short side of the calibration plate 3 shall not be less than 1 / 2 of the short side of the field of view of the first camera 1. Move the calibration plate within the plane 6 of the area to be measured and adjust the position and orientation of the first camera 1 so that the field of view of the first camera 1 covers one end of the plane 6 of the area to be measured.

[0024] Step 4: Move the calibration plate 3 within the plane 6 of the area to be measured so that it is in the overlapping area of ​​the shooting areas of the first camera 1 and the second camera 2. Adjust the position of the second camera 2 so that the field of view of the second camera 2 covers the remaining area of ​​the plane 6 of the measurement area, and make the overlapping area 7 of the images of the first camera 1 and the second camera 2 not less than 1 / 10 of the camera's field of view.

[0025] Step 5: Move the calibration plate 3 in the overlapping area 7 of the two camera images, and control the first camera 1 and the second camera 2 to simultaneously capture no less than 10 sets of images of the calibration plate 3. Move the calibration plate in the measurement area plane 6 so that it is within the field of view of the first camera 1 or the second camera 2, and control the first camera 1 or the second camera 2 to capture no less than 10 sets of images of the calibration plate 3.

[0026] Step 6: Establish a world coordinate system based on the image captured by the first camera 1. Based on the marker points of the common part of the calibration plate 3 in the images of the first camera 1 and the second camera 2, and based on the world coordinate system established by the image captured by the first camera 1, accurately place the image captured by the second camera 2 in the world coordinate system by moving and scaling, that is, determine the position of the image captured by the first camera 2 in the world coordinate system.

[0027] Step 7: Conduct a formal PIV test;

[0028] Step 8: Based on the position of the image captured by the second camera 2 in the world coordinate system obtained in Step 6, remove the overlapping area in the image captured by the second camera 2, and place it into the world coordinate system containing the image captured by the first camera 1, thus forming the original large field-of-view image of the tracer particles in the PIV experiment.

Claims

1. A method for stitching raw particle images for large field-of-view (PIV) measurements, characterized in that, The method includes the following steps: Step 1: Based on the size of the plane (6) of the area to be measured: a The long side of the plane of the region to be measured, b The imaging chip specifications of the first camera (1) and the second camera (2) of the PIV system are as follows: (The short side of the plane to be measured is shown.) m For the long side of the imaging chip specification, n The short side of the imaging chip, the proposed camera mounting position, and its distance from the plane of the measurement area (6) are defined. s Preliminary calculation of the focal length of the PIV camera lens f ; Step 2: Depending on the specific conditions of the PIV measurement area plane (6), install the two cameras of the PIV system horizontally or vertically in appropriate positions; Step 3: Select a calibration plate and place it within the field of view of the first camera (1) of the PIV system. The size of the short side of the calibration plate (3) is not less than 1 / 2 of the short side of the field of view of the first camera (1). Move the calibration plate within the plane (6) of the area to be measured and adjust the position and orientation of the first camera (1) so that the field of view of the first camera (1) covers one end of the plane (6) of the area to be measured. Step 4: Move the calibration plate (3) within the plane (6) of the area to be measured so that the overlapping area of ​​the shooting areas of the first camera (1) and the second camera (2) is located. Adjust the position of the second camera (2) so that the field of view of the second camera (2) covers the remaining area of ​​the plane (6) of the measurement area and the overlapping area (7) of the images of the first camera (1) and the second camera (2) is not less than 1 / 10 of the camera's field of view. Step 5: Move the calibration plate (3) in the overlapping area (7) of the two camera images, and control the first camera (1) and the second camera (2) to simultaneously capture no less than 10 sets of images of the calibration plate (3). Move the calibration plate in the plane (6) of the measurement area so that it is within the field of view of the first camera (1) or the second camera (2), and control the first camera (1) or the second camera (2) to capture no less than 10 sets of images of the calibration plate (3). Step 6: Establish a world coordinate system based on the image captured by the first camera (1). Based on the marker points of the common part of the calibration plate (3) in the images of the first camera (1) and the second camera (2), establish a world coordinate system based on the image captured by the first camera (1). By moving and scaling, accurately place the image captured by the second camera (2) in the world coordinate system, that is, determine the position of the image captured by the first camera (2) in the world coordinate system. Step 7: Conduct a formal PIV test; Step 8: Based on the position of the image captured by the second camera (2) in the world coordinate system obtained in Step 6, remove the overlapping area in the image captured by the second camera (2) and put it into the world coordinate system containing the image captured by the second camera (1) formed by the image captured by the first camera (1) to form the original large field of view image of the PIV experiment multi-camera tracer particles.

Images