## 1 Introduction  
Electromagnetic launch is an advanced launch method that utilizes electromagnetic forces to accelerate objects, and its launcher needs to deliver megajoule-level energy to the armature within a few milliseconds to push the projectile from rest to hypervelocity over a meter-scale distance [1]. As the core component of the launcher, the inner bore, which is composed of rails and insulators, will suffer from surface ablation [2], wear [3] aluminum deposition [4], structural bending [5], and other degradation phenomena under the repeated extreme conditions of high-speed, high-voltage, and high-current sliding electrical contact between the armature and rails [6]; ultra-high-speed lateral collision of the projectile [7]; and transient electromagnetic thermal shock [8]. These degradation phenomena affect the electrical contact performance between the armature and rails, the degree of collision between the projectile and barrel, and the launch directionality, leading to an increase in projectile exit perturbation, attitude destabilization, velocity reduction [9], and even the occurrence of projectile disintegration, bore burst, and other failures. In order to facilitate the study of the evolution patterns and mechanisms of these degradation phenomena [10], guide the matching design of the launcher and projectile [11], and develop the in-service capability for detecting, evaluating, and maintaining the health status of the inner bore [12], it is necessary to efficiently observe these degradation conditions of the inner bore without disassembling the launcher. Since these degradation phenomena are ultimately reflected in their deformation, the observation of bore degradation can begin with deformation detection. Compared to the unilateral rail surface deformation detection after disassembling the launcher [13; 14], the characteristics and challenges of non-disassembled deformation detection lie in the closed and narrow detection space, the absence of spatial localization references, the extension of the detection scope to the surface deformation around the bore, and the straightness along the launching direction. Moreover, as a health monitoring method, the detection system needs to consider rapidity and portability. In addition, electromagnetic launchers typically employ arc-surface rails and flat-surface insulators, and their bore profiles are significantly different from the circular inner profiles of conventional pipelines [15; 16; 17; 18; 19; 20], which also have their own specificity in the detection of bore deformation. [PERSON] et al. [21; 22] measured the spacing between the upper and lower rails based on the principle of the angular bisector by using a contact method. However, this method can only measure the spacing change at a certain point on the rail surface, and requires the assumption that the rail spacing changes uniformly within a certain length, which leads to significant assumption errors. [PERSON] et al. [23; 24] reconstructed the deformation of a bore surface by combining laser projection with binocular stereo vision, and utilized global correlation coding to enhance the completeness of matching results. Due to the necessity of accurate feature point matching in the images captured by the two cameras, this method faces significant data processing challenges, making it difficult to ensure stable and efficient operation of the measurement system. [PERSON] et al. [25] conducted measurements of a bore's three-dimensional dimensions based on the laser triangulation principle, and improved the detection efficiency by replacing point laser rotational forward scanning with ring-structured light scanning [26]. [PERSON] et al. [27] proposed a deviation correction method to address the issue of detection devices' self-deflection, but this method requires frequent external intervention during the measurement and data post-processing stages, resulting in low automation [28]. Additionally, it does not further consider the extraction of surface deformation and straightness.