CN1427245A - Plane measuring method based on single piece image - Google Patents

Abstract

A plane measurement method based on a single image, comprising the steps of: placing a template in the measured scene plane; shooting one or more images containing the template in the measured scene; extracting a known template in the image Information; calculate the mapping relationship between the measured plane and the image plane; calculate the coordinate value of any point in the scene and the distance between any two points according to the mapping relationship. The measurement method provided by the invention does not need to calibrate the camera parameters, and has the characteristics of simplicity, practicability, high measurement accuracy, good robustness, etc., making the vision-based measurement method practical.

Description

Plane Measurement Method Based on Single Image

technical field

The present invention relates to computer aided automatic measurement.

Background technique

In our daily life and in many fields, measurement, especially the measurement between two points in the same plane is essential, such as traffic accidents, criminal scenes, buildings, construction sites, etc., require a lot of measurement work . The traditional method is to use manual measurement, which is very time-consuming and prone to large measurement errors, and this measurement is also prone to unfair results due to the subjective factors of the measurers.

In recent years, with the development and application of computer vision, people have begun to explore the use of computer vision methods to measure through images. In this type of method, it is typical to reconstruct the three-dimensional structure of the scene under test by two or more images using stereo vision, but this method involves a classic problem in the field of computer vision, that is, the matching between multiple images. , so it is difficult to put into practical application. Another method is to manually measure the information of more than 4 control points in the scene plane in advance to calculate the projection matrix between the space plane and the image plane, and then measure through a single image. The measurement accuracy and control of this method The selection accuracy, location and number of points are directly related, but in practical applications, sometimes it is difficult to select control points, and the measurement accuracy of control points cannot be guaranteed.

Contents of the invention

The purpose of the present invention is to provide a measurement method based on a single image that is relatively simple, practical, has high measurement accuracy and robustness.

In order to achieve the above purpose, the plane measurement method based on a single image includes steps:

Place a template in the scene plane under test;

taking one or more images containing the template in the scene under test;

Extract known template information in the image;

Calculate the mapping relationship between the measured plane and the image plane;

Calculate the coordinate value of any point in the scene and the distance between any two points according to this mapping relationship.

The measurement method provided by the invention does not need to calibrate the camera parameters, and has the characteristics of simplicity, practicability, high measurement accuracy, good robustness, etc., making the vision-based measurement method practical.

Description of drawings

Figure 1 is a schematic diagram of several templates;

Fig. 2 is the flowchart of this measuring method;

Fig. 3 is a measurement scene diagram of the embodiment.

Specific Embodiments of the Invention

The present invention adopts a simple plane template, which contains 4 or more straight lines or line segments. The size of the template can be selected according to the size of the scene to be measured. There is no special requirement for the material of the template. Accompanying drawing 1 Several commonly used template examples are given. Put this template in the scene plane to be measured, take an image with an ordinary camera or a digital camera for measurement, and do not need to calibrate the camera parameters, if you can take multiple images from different angles, you can choose one of them Use a better image to measure or comprehensively use the measurement values of the same measured object in multiple images to improve the measurement accuracy.

This method effectively avoids the selection of control points, and directly uses the straight line information on the template when calculating the mapping relationship between the measured plane and the image plane, which can effectively improve the measurement accuracy and simplify the difficulty of image processing. It is beneficial to improve the automation degree of the whole measurement process. For an image, the method mainly includes steps such as image acquisition, template feature extraction, calculation of transformation matrix, and measurement, as shown in Figure 2. The specific description of each step is as follows: 1. Acquire the image

Put the template in the plane of the scene to be tested, take one or more images with an ordinary camera or a digital camera, and input the images into the computer with the help of a scanner or some special interface equipment. 2. Template feature extraction

Extract the required template information from the image by automatic or human-computer interaction method, that is, the straight line parameters on the template. Among them, Canny, Robert, Sobel and other edge detection operators can be used to extract edge information, and then Hough transform, least squares, maximum likelihood estimation and other methods can be used to obtain line parameters. 3. Calculate the transformation matrix

The straight line or line segment information on the template adopted by the method is measurable, and its measurement parameters are stored in the computer. According to the corresponding relationship between the straight line or line segment on the template and the image straight line or line segment extracted in the second step, the mapping relationship matrix M from the scene plane to the image plane is obtained. 4. Measure

For any point on the image, the coordinate value of the corresponding point in the scene can be obtained by using the inverse transformation M ^-1 of the mapping relationship matrix obtained in the third step, and the distance between any two points in the scene can be calculated. At the same time, the error range of each measurement result can be given according to the uncertainty analysis of each step.

Example

Figure 3 is an image of a tested scene, in which the template is composed of two rectangles. According to the method of the present invention, eight sides of two rectangles are automatically extracted in the image and the mapping relationship between the measured plane and the image plane is calculated, and the mapping relationship can be used by selecting two points in the image with the mouse Find the distance between these two points in the scene directly from the image. For example: D1, the true length of D2 are respectively 77.85cm and 189.78cm, and the measured value that draws with the inventive method is respectively 77.72cm and 191.02cm, and the relative error of measurement is respectively 0.17% and 0.65%, and this is fully achievable required for measurement accuracy.

Claims (3)

1. A plane measurement method based on a single image, comprising steps: Place a template in the scene plane under test; taking one or more images containing the template in the scene under test; Extract known template information in the image; Calculate the mapping relationship between the measured plane and the image plane; Calculate the coordinate value of any point in the scene and the distance between any two points according to this mapping relationship. 2. The plane measuring method based on a single image according to claim 1, characterized in that the placed template contains 4 or more straight lines or line segments. 3. The plane measuring method based on a single image according to claim 2, characterized in that said straight line or line segment is a side of a plane figure, such as a rectangle, a square, a triangle, etc. and the figures produced by a combination thereof.

Images