# Optimization Method of Square Hole Measurement Based on Generalized Point Photogrammetry
## 1 Introduction  
In recent years, with the rapid development of artificial intelligence [1], machine learning [2], cloud computing [3] and other technical fields, photogrammetry has become more and more widely used in engineering [4]. Engineering problems are usually more complex than theoretical problems, and more factors are considered. The traditional point-based photogrammetric method is not enough to solve engineering problems; therefore, the generalized photogrammetric method based on line features is proposed [5]. Generalized photogrammetry originated in the 19 th century. After decades of development in theoretical research, it has gradually developed from the classic point-based photogrammetry model to point-line hybrid photogrammetry and generalized point photogrammetry. With the development of big data and the arrival of intelligent photogrammetry, photogrammetry can use more homonymous features to complete the measurement calculation. Intelligent high-precision measurement is urgently needed in engineering. This measurement method not only improves the work efficiency and the safety of measurement, but also greatly reduces the measurement cost. With the performance improvement of computers, sensors, transmission equipment and other hardware [6], a large number of traditional measurement methods [7] will be replaced by intelligent high-precision photogrammetry. Intelligent photogrammetry has many applications in target recognition [8], monitoring [9], unmanned driving [10], three-dimensional modeling [11], precision measurement [12], emergency response [13] and other aspects. Traditional photogrammetry involves only physical points, such as corners, intersections between lines, centers and so on. The calculation process of traditional photogrammetry is also based on the collinearity of points. However, in engineering, point features [14] are usually ideal features, and it is not easy to extract accurate coordinates of points. There are a lot of line features in engineering [15]. These features exist in the form of straight lines or curves, from which it is easy to extract accurate information. Especially when multiple images are used for calculation in engineering, it is better to use a large number of line features for adjustment. Line features can be divided into straight line features and curve features. There are many straight line features in urban planning and housing surveys [16]. There are many curve features in roads, mountains and rivers [17]. Mathematically, line features and point features can be considered as \"points\" in a broad sense. From the collinear equation in photogrammetry [4], the coordinates of space points can be regarded as the parameter equation of the line, so that the line features meet the collinear equation. [PERSON] of Wuhan University completed automatic three-dimensional reconstruction of cylinders using the principle of generalized photogrammetry [18], [PERSON] of Wuhan University completed three-dimensional reconstruction of circles and rounded rectangles using the principle of generalized photogrammetry [19], and [PERSON] used the principle of generalized photogrammetry to study space intersection and resection [20]. In addition, [PERSON] also proposed generalized photogrammetry based on multi-source remote sensing data of the sky and the ground [21]. The application of general photogrammetry will be more and more extensive. In recent years, prefabricated bridges have been rapidly promoted in China [22]. At present, the construction site mainly relies on workers to use the total station to complete measurement in the whole process [23]. As a widely used optical instrument, the precision of the total station can meet the construction requirements, but its efficiency is too low. For the on-site construction environment, the field of vision of the total station is too small to measure the coordinates of the points directly.