The collinearity equation of photogrammetry is based on the number of photography center, ground point and corresponding () three points on a straight line.

The collinearity equation is a mathematical relationship that indicates that the object point, the image point and the projection center (usually the lens center of a photo) are located on a straight line, and it is one of the most basic formulas in photogrammetry.

The application of photogrammetry is as follows:

1. Ground photogrammetry is used for topographic survey: Ground photogrammetry is mainly used for small-scale topographic survey, not for national basic map mapping.

2. Application of close-range photogrammetry: Using close-range photogrammetry technology, the vertical image of the target is photographed with a digital camera, the three-dimensional coordinates of the image control points are obtained with a prism-free electronic total station, and then the digital image is processed with software. This method can not only reduce the workload of field work, shorten the time, but also reduce the manpower.

The application of close-range photogrammetry in slope deformation monitoring belongs to the field of civil engineering construction. Using close-range photogrammetry technology to monitor slope engineering can evaluate slope construction quality problems and slope stability during use, predict its danger degree, and provide relevant information for owners, construction units and supervisors.

3. Application of close-range photogrammetry in mine survey: This method is low in cost, simple and easy to operate, and conforms to China's national conditions and the actual situation of production departments. Photos are informative, large in capacity, and the images are real and intuitive, which can reduce the time of underground operation and improve work efficiency. Its accuracy is the traditional method.

4. The function of close-range photogrammetry in automatic driving: put multiple digital cameras in different parts of the car, so that the internal orientation elements can be obtained in advance. As long as the camera content is imported into the computer, stereo simulation can be carried out by using image correlation.