Initial Alignment Research Articles

Learning feature descriptors for pre- and intra-operative point cloud matching for laparoscopic liver registration.

In laparoscopic liver surgery, preoperative information can be overlaid onto the intra-operative scene by registering a 3D preoperative model to the intra-operative partial surface reconstructed from the laparoscopic video. To assist with this task, we explore the use of learning-based feature descriptors, which, to our best knowledge, have not been explored for use in laparoscopic liver registration. Furthermore, a dataset to train and evaluate the use of learning-based descriptors does not exist. We present the LiverMatch dataset consisting of 16 preoperative models and their simulated intra-operative 3D surfaces. We also propose the LiverMatch network designed for this task, which outputs per-point feature descriptors, visibility scores, and matched points. We compare the proposed LiverMatch network with a network closest to LiverMatch and a histogram-based 3D descriptor on the testing split of the LiverMatch dataset, which includes two unseen preoperative models and 1400 intra-operative surfaces. Results suggest that our LiverMatch network can predict more accurate and dense matches than the other two methods and can be seamlessly integrated with a RANSAC-ICP-based registration algorithm to achieve an accurate initial alignment. The use of learning-based feature descriptors in laparoscopic liver registration (LLR) is promising, as it can help achieve an accurate initial rigid alignment, which, in turn, serves as an initialization for subsequent non-rigid registration.

In-motion initial alignment method using Cayley–Kalman filter on special orthogonal group

Aiming at the in-motion initial alignment problem of strapdown inertial navigation system (SINS), this paper proposed a precise direct in-motion alignment method based on attitude matrix representation and Cayley–Kalman filter on the special orthogonal group. There are two innovations in this paper. First, as an element of the special orthogonal group [Formula: see text], the error attitude matrix is used to construct an in-motion alignment model, and it is transformed into the vector space to represent the attitude error state. The error matrix was used as a state to decrease the influence of the state-dependent problem. Second, this method uses the Cayley transform to replace the Taylor expansion to derive the update equation, which is a no approximation mapping relation to assure accuracy when deriving the filtering algorithm. Simulation and experimental results demonstrate the proposed alignment method has advantages over the existing methods in alignment accuracy and alignment time and performs well in the in-motion alignment process of SINS.

Fast Point Cloud Registration Method with Incorporation of RGB Image Information

Point cloud registration has a wide range of applications in 3D reconstruction, pose estimation, intelligent driving, heritage conservation, and digital cities. The traditional iterative closest point (ICP) algorithm has strong dependence on the initial position, poor robustness, and low timeliness. To address the above issues, a fast point cloud registration method that incorporates RGB image information is proposed. The SIFT algorithm is used to detect feature points of point clouds corresponding to the RGB image, followed by feature point matching. The RANSAC algorithm is applied to remove erroneous point pairs in order to calculate the initial transformation matrix. After applying a pass-through filter for noise reduction and transiting down with a voxel grid, the point cloud is subjected to rotation and translation transformation for initial registration. On the basis of initial alignment, the FR-ICP algorithm is utilized for achieving precise registration. This method not only avoids the problem of ICP easily getting stuck in local optima, but also has higher registration accuracy and efficiency. Experimental studies were conducted based on point clouds of automotive parts collected in real scenes, and the results showed that the proposed method has a registration error of only 0.487 mm. Among the same group of experimental point clouds with comparable registration error, the proposed method showed a speed improvement of 69%/48% compared to ICP/FR-ICP with regard to registration speed.

Alignment scheme optimization when gyro accuracy inconsistency for inertial navigation system

Rotation modulation technology can average out constant errors in fiber optic gyro (FOG) rotational inertial navigation system (RINS). As a result, angle random walk (ARW) of FOGs plays a significant role in the precision of initial alignment. Using different gyros as horizontal gyros gradually transitioned from theory to practical application with the advancement of design philosophy. The theoretical formula between azimuth alignment accuracy and random walk coefficients (RWCs) of two horizontal gyros is deduced in this paper. A completely new multiple rotations and stationary alignment scheme is suggested. A recursive least-squares filter with azimuth variation in body reference frame and accelerometer outputs in navigation frame as measurements is constructed. The efficiency of this method is demonstrated through simulation and experimentation. The findings demonstrate that using this formula and alignment scheme, azimuth alignment accuracy could be greatly increased, which can be improved by 10.85% compared to common continuous rotation alignment scheme.

Correction of class III malocclusion using enmasse distalization with tad

Skeletal class III malocclusion in adult patients are generally managed by orthognathic surgery. However, the prognosis is poor when the patient refuses surgical line of treatment. In such cases orthodontic camouflage through dentoalveolar compensation may be attempted. Presently, with the advent of stationary anchorage, en mass distalization appears to be a common choice. This article demonstrates an en mass distalization carried out in the upper and lower arches in a class III skeletal case, refusing surgery. After initial levelling and alignment, TADs (temporary anchorage devices) were placed bilaterally mesial to the first molars in upper and lower arches. After a month, distalization was initiated with 300 gms force applied per side using elastomeric chain. At the end of the treatment, the anterior cross bite and crowding was resolved and the patients profile improved. Thus, en masse distalization with TADs appears be a good choice in class III skeletal cases refusing surgery. It is minimally invasive and cost effective.

Automatic rigid image Fusion of preoperative MR and intraoperative US acquired after craniotomy

BackgroundNeuronavigation of preoperative MRI is limited by several errors. Intraoperative ultrasound (iUS) with navigated probes that provide automatic superposition of pre-operative MRI and iUS and three-dimensional iUS reconstruction may overcome some of these limitations. Aim of the present study is to verify the accuracy of an automatic MRI – iUS fusion algorithm to improve MR-based neuronavigation accuracy.MethodsAn algorithm using Linear Correlation of Linear Combination (LC2)-based similarity metric has been retrospectively evaluated for twelve datasets acquired in patients with brain tumor. A series of landmarks were defined both in MRI and iUS scans. The Target Registration Error (TRE) was determined for each pair of landmarks before and after the automatic Rigid Image Fusion (RIF). The algorithm has been tested on two conditions of the initial image alignment: registration-based fusion (RBF), as given by the navigated ultrasound probe, and different simulated course alignments during convergence test.Results Except for one case RIF was successfully applied in all patients considering the RBF as initial alignment. Here, mean TRE after RBF was significantly reduced from 4.03 (± 1.40) mm to (2.08 ± 0.96 mm) (p = 0.002), after RIF. For convergence test, the mean TRE value after initial perturbations was 8.82 (± 0.23) mm which has been reduced to a mean TRE of 2.64 (± 1.20) mm after RIF (p < 0.001).ConclusionsThe integration of an automatic image fusion method for co-registration of pre-operative MRI and iUS data may improve the accuracy in MR-based neuronavigation.

A novel adaptive nonlinear Kalman filter scheme for DVL-aided SINS alignment in underwater vehicles

The rapid and accurate initial alignment of a strapdown inertial navigation system (SINS) aided by a Doppler velocity logger (DVL) still poses a significant challenge in unmanned underwater vehicle navigation. In this study, a novel adaptive nonlinear filtering alignment scheme is developed for a SINS with a large misalignment angle. In previous studies, the frame-inconsistency problem of the nonlinear SINS error model was neglected. Thus, a modified nonlinear error model of a SINS is derived here rigorously as the process model of the nonlinear Kalman filter. In addition, the noise amplification of applying Sage-Husa adaptive Kalman filter (SHAKF) in alignment is analyzed, and a novel arctangent fading memorial factor is introduced to dynamically adjust the weight of current measurements. Simulations and field experiments indicate that the proposed algorithm is efficient in underwater DVL/SINS in-motion alignment. The alignment accuracy and convergence rate of the modified model are significantly improved compared to those of the traditional model. The arctangent fading memorial SHAKF can reliably estimate the measurement noise and improve the performance of alignment.

Rapid Initial Heading Alignment for MEMS Land Vehicular GNSS/INS Navigation System

For the low-cost microelectromechanical system (MEMS) inertial navigation system (INS) and global navigation satellite system (GNSS) integrated system in land vehicular applications, quick and accurate coarse alignment is still a challenge, especially for a host vehicle that moves at low speed under low dynamics. In this paper, we propose an in-motion coarse initial heading alignment algorithm for the low-cost MEMS INS aided by the GNSS, which is specifically designed for land vehicular conditions. The principle of the proposed method is straightforward when considered in the context of trajectory matching: the MEMS can compute a relative vehicle trajectory through a dead reckoning (DR) calculator using the gyro-derived attitude solution and the travel distance, and the GNSS can provide an absolute vehicle trajectory through its positioning solution. The initial heading is then computed by comparing these DR-indicated and GNSS-indicated trajectories. The proposed algorithm is verified using a civilian vehicle, a wheeled robot, and an agricultural tractor under different motion and dynamic conditions. The results show that the initial heading could be quickly determined with an accuracy of 0.25°, 0.6°, and 1.6° at a 98.6% confidence level within 5 s for the car, robot and tractor tests, respectively.

The relationship between salivary alpha-amylase, nitric oxide, pain and anxiety-induced stress in patients during dental treatment.

Pain and anxiety are the most reported negative effect of orthodontic treatment which can influence the quality of life and are responsible for the discontinuation of treatment. These unpleasant experiences raise the stress levels reflected by the increase in the concentration of salivary alpha-amylase and nitric oxide. These can be assessed through various subjective methods which have limited value as it depends on the patient's honesty, assessing whether using objective methods are reliable. To assess pain and anxiety-induced stress levels using both physiological (Salivary alpha-amylase and Salivary nitric oxide) and psychological testing instruments (Visual analog scale and State Trait Anxiety Inventory Y6) during the initial phases of fixed orthodontic treatment. A total of 30 patients were included. Pain and anxiety instruments were applied and saliva samples were collected from patients before and after separator placement, before and 48 h after archwire insertion and 1 month after archwire insertion. The mean values of alpha-amylase (235.3600), nitric oxide levels (2.060) and pain scores (7.8667) were higher 48 h after archwire insertion (T3) which are statistically significant, P = 0.00. Anxiety scores (57.7000) were high before separator placement (T0). No statistically significant correlation was found among pain and alpha-amylase, anxiety and nitric oxide levels. Initial alignment phases of fixed orthodontic treatment affect patients' anxiety and stress levels. The findings could be a result of the psychological stress due to procedures in the initial phases of the treatment.

An Optimal Estimation Approach for MEMS INS Performance Improvements Based on Single-FOG Monitoring

A new approach is proposed for MEMS INS performance improvement, which uses a Fiber Optic Gyro to monitor the triad of MEMS gyros and compensates the errors of the MEMS INS in real time by using an elaborated Kalman filter. A state space model of single-FOG monitored MEMS INS is developed, and the observability of the model is analyzed for the Kalman filter. Simulated and experimental tests are carried out to evaluate the effectiveness of the proposed approach. The test results show that this method can effectively reduce the errors of the MEMS gyros and dramatically improve the initial alignment and navigation performances of the MEMS INS.

An Improved In-Motion Coarse Alignment Method for SINS/GPS Integration with Initial Velocity Error Suppression.

The integrated system with the strapdown inertial navigation system (SINS) and the global positioning system (GPS) is the most popular navigation mode. It has been used in many navigation fields. Before the integrated system works properly, it must determine the initial attitude for SINS. In SINS/GPS-integrated systems, the navigational velocity can be used to carry out the initial alignment when the system is installed in the in-motion vehicle. However, the initial velocity errors are not considered in the current popular in-motion alignment methods for SINS/GPS integration. It is well-known that the initial velocity errors must exist when the initial velocity is obtained from the GPS outputs. In this paper, an improved method was proposed to solve this problem. By analyzing the original observation vectors in the in-motion coarse alignment method, an average operation was used to construct the intermediate vectors, and the new observation vector can be calculated by subtracting the intermediate vector from the original observation vector. Then, the initial velocity errors can be eliminated from the newly constructed observation vector. Thus, the interferences of the initial velocity errors for the initial alignment process can be suppressed. The simulation and field tests are designed to verify the performance of the proposed method. The tests results showed that the proposed method can obtain the higher accurate results than the current methods when the initial velocity is considered. Additionally, the results of the proposed method were similar to the current methods when the initial velocity errors were not considered. This shows that the initial velocity errors were eliminated effectively by the proposed method, and the alignment accuracy were not decreased.

A SE(2)-based transfer alignment for large installation misalignment angle

Transfer alignment is the optimal solution for initial alignment of shipborne or airborne weapons. The need for transfer alignment is increasing at large installation misalignment angles. Traditional linear models have large attitude errors at large installation misalignment angles, nonlinear algorithms are computationally intensive and difficult to be widely used, and quaternion optimization algorithms are sensitive to noise. In this paper, the Lie group theory is introduced for the first time in the study of transfer alignment. The attitude and velocity are represented as the Group of Direct Planar Isometries (SE(2)), and then the SE(2)-based error vectors are constructed by log-linearization. The SE(2)-based linear transfer alignment algorithm is developed for large installation misalignment conditions. The computational effort of the proposed algorithm is very small due to its linear structure, and it has strong engineering application value. The simulation and field test are conducted to illustrate the effectiveness of the proposed transfer alignment algorithm.

In silico characterization of the psilocybin biosynthesis pathway

Nearly all mushrooms of the Psilocybe genus contain the natural product psilocybin, which is a psychoactive alkaloid derived from l-tryptophan. Considering their use in ancient times, as well as their psychedelic properties, these mushrooms have re-emerged with psychotherapeutic potential for treating depression, which has triggered increased pharmaceutical interest. However, the psilocybin biosynthesis pathway was only recently defined and, as such, little exists in the way of structural data. Accordingly, the aim of this study was to structurally characterize this pathway by generating homology models for the four Psilocybe cubensis enzymes involved in psilocybin biosynthesis (PsiD, a decarboxylase; PsiH, a monooxygenase; PsiK, a phosphotransferase; PsiM, a methyltransferase). Following initial model generation and alignment with the identified structural templates, repeated refinement of the models was carried out using secondary structure prediction, geometry evaluation, energy minimization, and molecular dynamics simulations in water. The final models were then evaluated using molecular docking interactions with their substrates, i.e., psilocybin precursors (l-tryptophan, tryptamine, 4-hydroxytryptamine, and norbaeocystin/baeocystin), all of which generated feasible binding modes for the expected biotransformation. Further plausibility of the psilocybin → aeruginascin, 4-hydroxytryptamine → norpsilocin, and tryptamine → N,N-dimethyltryptamine conversions, all mediated by the generated model for PsiM, suggests valid routes of formation for these key secondary metabolites. The structural characterization of these enzymes and their binding modes which emerged from this study can lead to a better understanding of psilocybin synthesis, thereby paving the way for the development of novel substrates and selective inhibitors, as well as improved biotechnological manipulation and production of psilocybin in vitro.

Cervical Spinal Immobilization: A Head-to-Head Comparison of a One-Step Spray-on Foam Splint Versus Structural Aluminum Malleable Splint Immobilization.

Cervical spine immobilization in a low-resource environment is difficult secondary to limited equipment, prolonged transportation, and secondary complications. A structural aluminum malleable (SAM) splint is commonly utilized because of its availability and multipurpose intention. A one-step spray-on foam immobilization technique (Fast Cast) has been shown to be effective in lower-extremity splinting. The aim of this study was to demonstrate the ability of the Fast Cast to effectively immobilize the cervical spine in a head-to-head comparison against the SAM splint. We hypothesized that there would be no difference in surgeon scoring between Fast Cast and SAM splints for the immobilization of the cervical spine. This was a cadaveric experimental comparative study that compared a SAM splint versus Fast Cast for the immobilization of an unstable cervical spine. Each of the three cadaveric specimens had a corpectomy without fixation performed. A board-certified emergency medicine physician specialized in disaster medicine performed all SAM immobilizations. An orthopedic surgeon performed Fast Cast immobilizations. Each method of immobilization was done on each cadaver. Lateral fluoroscopic imaging was taken before and after immobilization and after log roll/gravity stress. Five board-certified orthopedic surgeons served as graders to independently score each splint. A 5-point Likert scale based on 10 splinting criteria (50 total points possible) was utilized to evaluate cervical spine immobilization. The lead statistical analyst was blinded to the immobilization groups. The statistical significance was assessed via a Wilcoxon signed-rank test and chi-square Fisher's exact test with significance between groups set at α < .05. Inter-rater reliability of the Likert scale results was assessed with the interclass correlation coefficient. Inter-rater reliability for the current Likert scale in the evaluation of cervical spine stabilization was good (interclass correlation coefficient = 0.76). For the cumulative Likert scale score, Fast Cast (32 [28-34]) exhibited a higher total score than SAM (44 [42-47]; P < .01). Likewise, Fast Cast exhibited a greater likelihood of higher Likert scores within each individual question as compared to SAM (P ≤ 0.04). In 100% of cases, raters indicated that Fast Cast passed the gravity stress examination without intrinsic loss of reduction or splinting material, whereas 33% of SAM passed (P < .01). In 100% of cases, raters indicated that Fast Cast passed the initial radiographic alignment following immobilization, whereas 66% of SAM passed (P = .04). In 100% of cases, raters indicated that Fast Cast passed radiographic alignment after the gravity stress examination, whereas 47% of SAM passed (P < .01). The Fast Cast exceeded our expectations and was shown to be rated not equivalent but superior to SAM splint immobilization for the cervical spine. This has significant clinical implications as the single-step spray-on foam is easy to transport and has multifaceted applications. It also eliminates pressure points and circumferential wrapping and obstruction to airway/vascular access while immobilizing the cervical spine and allowing for radiographic examination. Further studies are needed for human use and application.

The Effect of Minor Adjustments to Tibial and Femoral Component Position on Soft Tissue Balance in Robotic Total Knee Arthroplasty

BackgroundIdeal goals for alignment and balance in total knee arthroplasty (TKA) remain controversial. We aimed to compare initial alignment and balance using mechanical alignment (MA) and kinematic alignment (KA) techniques and to analyze the percentage of knees that could achieve balance using limited adjustments to component position. MethodsProspective data on 331 primary robotic TKAs (115 MAs and 216 KAs) were analyzed. Medial and lateral virtual gaps were recorded in both flexion and extension. A computer algorithm was used to calculate potential (theoretical) implant alignment solutions to achieve balance within 1 millimeter (mm) without soft tissue release given an alignment philosophy (MA or KA), angular boundaries (±1, ±2, or ±3°), and gap targets (equal gaps or lateral laxity allowed). The percentage of knees that could theoretically achieve balance was compared. ResultsLess than 5% of TKAs were initially balanced. Limited adjustments to component position increased the percentage of TKAs that could be balanced in a graduated manner, with no difference between MA and KA start points: adjustments of ±1 (10% versus 6%, P = .17), ±2 (42% versus 39%, P = .61), or of ±3 (54% versus 51%, P = .66). A higher percentage of TKAs could be balanced when a greater range for lateral gap laxity was allowed. Balancing from KA resulted in increased joint line obliquity in the final implant alignment. ConclusionA high percentage of TKAs can be balanced without soft tissue release using minor adjustments to component position. Surgeons should consider the relationship between alignment and balance goals when optimizing component positioning in TKA.

A Polar Integrated Alignment Assisted by DVL Under Large Azimuth Misalignment

The gravity tends to coincide with the earth’s rotation vector in the polar region, degrading the coarse alignment azimuth of the strapdown inertial navigation system (SINS) to a large misalignment. Under a large azimuth misalignment, the linear error model inevitably renders unacceptable theoretical errors in the integrated alignment. In addition, polar region challenge such sensors as a star sensor of celestial navigation, which fails to provide high-precision attitude reference for integrated alignment. Therefore, in allusion to the misalignment mentioned above based on SINS for the polar region, an integrated alignment algorithm is proposed, assisted by the Doppler Velocity Log (DVL). Notably, the work first investigates the extent to which azimuth accuracy deteriorates in the polar region. On the premise of large azimuth misalignment, the nonlinear error model under the transverse frame is derived from the ellipsoid earth model. Additionally, the state and measurement models are constructed, combined with the velocity of DVL as an observation. An adaptive measurement variance matrix is designed for the unscented Kalman filter (UKF) to estimate the attitude error. Eventually, the semi-physical experiments demonstrate that the proposed algorithm significantly improves the initial alignment accuracy of the polar region.

Measurement of microfibril angle in plant fibres: Comparison between X-ray diffraction, second harmonic generation and transmission ellipsometry microscopies

The orientation of cellulose microfibrils within plant fibres is one of the main factors influencing their mechanical properties. As plant fibres are more and more used as reinforcement for agro-composites, their mechanical properties have a strong influence on the final composite properties. It is, therefore, of interest to obtain reliable information about the microfibril angle (MFA) to better support the choice of fibres depending on the product requirements. In the present study, the reliability and specificities of three non-destructive methods that allow analysis on the same fibre glued on a holder; X-ray diffraction (XRD), second harmonic generation (SHG) and transmission ellipsometry (TE) microscopy; are investigated. Three types of plant fibres, with both low (nettle), and high (cotton, sisal) MFA values, are compared and their geometry and biochemical composition are characterised. The results obtained on the same fibre confirm that MFA analysis remains tedious and that despite their limitations, the methods are complementary depending on the information requested. Indeed, SHG is recommended for direct, qualitative and plane-selective mapping of heterogeneities in macrofibril orientations at various depths. However, reliable quantitative results with SHG depend on the initial image quality and could benefit from further image processing refinement. On the contrary, XRD and TE measure MFAs over the entire fibre thickness and provide variations along the fibres if a sufficient optical/spatial resolution is reached. Regarding the characterization of intrinsic defects in plant fibres, both SHG and TE suffer from uncertainties induced by the disorganization of the microfibril network and the lack of symmetry between the front and back fibre walls. Finally, all techniques prove to be dependant on the initial fibre alignment and geometry (i.e. twisting, double fibre configuration or form factor) which vary along the fibre length and should be carefully taken into account.

Long-Term Effects of Botulinum Toxin A for Horizontal Concomitant Strabismus in Chinese Children

ABSTRACT Introduction For childhood strabismus, early surgical intervention improves both motor and sensory outcomes. Botulinum toxin type A (BTX-A) injection is an alternative to incisional surgery that is fast, less invasive, and preserves a more normal biomechanical construct. This study was undertaken to assess the safety and effectiveness of BTX-A for horizontal concomitant strabismus in children in our institution. Patients and Methods Records of all children less than age 18 years with follow-up at least 12 months who were treated with BTX-A for horizontal concomitant strabismus at Beijing Children’s Hospital between December 2014 and February 2021 were reviewed retrospectively. Bilateral injections of BTX-A (Henli, 1.25 IU to 5 IU/0.1 ml) were made into the medial or lateral rectus muscles according to the angle of deviation. Reinjection was permitted if the initial alignment was not satisfactory within 1 to 6 months post-injection. Motor success was defined as a final misalignment ≤10 PD. Sensory success was defined as the presence of any evidence of sensory fusion, distance stereopsis, or near stereopsis at the last visit. Results Seventy-one patients were included. Fifty-two had esotropia, and 19 had exotropia. There was a significant decrease in the angle of deviation in all treated patients. The overall motor success rate was 60.6%. The motor success rate was highest in children with esotropia <50 PD (81.5%). Motor success was better for children with partially accommodative esotropia and acquired non-accommodative esotropia (80%, 83.3%, respectively) than for children with infantile esotropia (47.4%). Compared with the esotropia group, the fusion was significantly higher in the exotropia group (p = .007), and the proportion of patients with stereoacuity of better than 100 sec arc was higher also in the exotropia group (71.4%, p = .007), evidence of sensory outcomes were significantly better in the exotropia group. Complications were few. Twenty patients (28.2%) developed transient ptosis after injections; transient vertical deviations were seen in 3 patients (4.2%); and subconjunctival hemorrhage was seen in 5 patients (7%). Conclusions BTX-A appears to be an effective treatment for the management of horizontal strabismus with motor outcomes best in children with acquired smaller-angle esodeviations. Children with exodeviations had better sensory outcomes in this cohort. A randomized controlled study comparing incisional surgery to BTX-A will be important for guiding future treatment decisions.

Point cloud registration based on concave hull association

ABSTRACT This letter presents a point cloud coarse registration method based on concave hull association. The assumption is that some internal points may be variable in different scans due to self-occlusion, but the hull vertices in overlap regions are consistent. Therefore, we only use the vertices of the concave hulls to find feature associations and reduce the number of wrong correspondences. Firstly, the method extracts the concave hulls and calculatecalculates the unique feature descriptors for each vertex of the hulls. Then, we use the sample consensus initial alignment algorithm to achieve feature matching and find the coarse registration parameters. The proposed method has been verified on different datasets and compared with state-of-the-art algorithms. The experiments demonstrate that the proposed algorithm eliminates unnecessary correspondences and obtains high efficiency and robustness.

Fast Two-position Initial Alignment of SINS Based on CKF

In practical vehicle applications, the initial alignment environment of SINS is more complicated, and the coarse alignment accuracy is not high due to carrier sloshing, which leads to the filtering problem of nonlinear system in fine alignment. The traditional two-position alignment method based on EKF is no longer applicable. In this paper, a fast two-position alignment method of SINS based on CKF is proposed. Use two CKFs for state estimation at two locations respectively, then the error parameters are solved through the spatial relationship between the two positions. The simulation shows that using CKF improves accuracy compared to EKF. Verified by experiment, the two-position alignment method based on CKF can better adapt to the nonlinear system, which can be applied in practical engineering.