99 results about "Star catalogue" patented technology

The invention discloses a multi-modal information fusion odometer construction method for star catalogue positioning, and relates to the technical field of star catalogue patroller positioning. The method comprises the following steps: carrying out space joint calibration on a monocular camera, a laser radar and an inertial measurement unit, reconstructing a laser radar point cloud by using a timestamp of a camera image, and realizing time synchronization of the camera image and the laser radar point cloud; establishing an IMU pre-integration error model; and performing motion compensation distortion removal on the laser point cloud by using an IMU pre-integration result, and extracting geometric features of the distorted laser point cloud based on a neighbor region smoothness calculation method of a fixed measurement distance. By researching a multimodal information fusion odometer method, the accumulative error of motion measurement is reduced, the positioning precision and stability are improved, technical support is provided for design and development of a star catalogue navigation system, and the problems that a single-modal star catalogue positioning method is weak in environment adaptive capacity and poor in algorithm generalization are solved.

The invention discloses a global enhancement method for a wide-area astronomical image. The method comprises the following steps: carrying out high-frame-frequency image acquisition on a starry sky area; converting the reference star from a star catalogue position to an observation position, and resolving a linear negative film model; geometric distortion correction is carried out based on the resolving result; based on the image after geometric distortion correction, matching and identifying a reference star in a full view field, and obtaining celestial coordinate information of all fixed star images in the view field; on the basis of celestial coordinate information, correcting a poorer astronomical effect of the astronomical image, establishing an ideal coordinate system taking the center of a view field as a tangency point, and projecting a time sequence observation image to the ideal coordinate system; translating the processed graph, accumulating all translated images, and averaging all accumulated pixel positions to realize image superposition enhancement, thereby effectively improving the dynamic range of a detector and the detection capability of a wide-area astronomical observation system; and meanwhile, the signal-to-noise ratio of the astronomical image can be effectively improved, and the astronomical image centering and light measuring precision can be further improved.

A method of generating a simulated image for training a model to detect resident space objects (RSOs), a method of training the model, and a method of detecting RSOs are provided. The method includes generating a foreground of the simulated image including RSOs by calculating coordinates of an imaging satellite at a given time, determining an area of interest given a field of view (FOV) of the imaging satellite, and calculating coordinates of all RSOs and saving the coordinates if the RSO is within the area of interest. The method further includes generating a background of the simulated image including stars by querying a star catalogue database for coordinates of all stars that fall inside the FOV, adding noise, and translating RSO and star coordinates to pixel coordinates. The method further includes generating the simulated image by choosing an imaging mode, setting an exposure time, and rendering the simulated image.

The invention provides a star catalogue file generation method and device, a celestial body data query method and device, computer equipment and a storage medium. The star catalogue file generation method comprises the steps of obtaining star catalogue data; dividing the celestial sphere surface area corresponding to the plurality of celestial bodies into a plurality of local areas, and determining an identifier of each local area; determining an identifier matched with each celestial body data according to the right ascension and declination included in the celestial body data and the identifier of each local area in the celestial sphere surface area; sorting the celestial body data of the plurality of celestial bodies based on the identifiers corresponding to the celestial body data; and writing the sequenced celestial body data of the plurality of celestial bodies into an initial column storage file matched with the identifier to obtain a target file stored with the celestial body data, and generating file index information corresponding to the target file. The celestial body data is stored by utilizing the column type storage file, so that the problems of high maintenance cost and high use threshold caused by utilizing a database to store data are relieved while the data query efficiency is guaranteed.

The invention discloses an astronomical cross identification method based on spherical trapezoidal division, and the method comprises the steps: S1, taking a unit spherical surface as a celestial sphere, dividing the celestial sphere into a plurality of strips parallel to an equatorial line, and determining the right ascension span of each strip for the transverse segmentation of the strip; s2, dividing each strip into a same spherical isosceles trapezoid with two waists perpendicular to the equator, and taking the same spherical isosceles trapezoid as a sky area; s3, determining an index of each sky area; s4, dividing a star catalogue A and a star catalogue B, and creating a zipper type hash table based on the row number of the star catalogue B; s5, mapping each celestial body in the star catalogue B into a linked list in a hash table in a multi-thread parallel mode, and inserting celestial body data into the linked list by means of a two-stage insertion strategy; s6, mapping each celestial body in the star catalogue A into a linked list in a group of hash tables in a multi-thread parallel mode, and traversing to obtain celestial body IDs of which the spherical distance is smaller than the error radius; the method not only can completely avoid the problem of result omission, but also can greatly improve the astronomical cross identification calculation performance.

The embodiment of the invention discloses an all-day and all-world time measurement method and device. A specific embodiment of the method comprises the following steps: constructing a short-wave infrared astronomical survey star catalogue; constructing a short-wave infrared astronomical geodetic survey star database according to the short-wave infrared astronomical survey star catalogue; optimizing the short-wave infrared astronomical geodetic survey star library to obtain an optimized short-wave infrared astronomical geodetic survey star library, and correcting atmospheric refraction errors in the optimized short-wave infrared astronomical geodetic survey star library; carrying out all-day fixed star point coordinate extraction on the shot multi-frame daytime star map to obtain fixed star point coordinates; and according to the star point coordinates of the fixed star, carrying out all-day astronomical observation world time calculation on the observation fixed star to obtain all-day world time. According to the embodiment, unified comparison of multi-period monitoring data is realized, and the engineering practicability of a monitoring result is improved.

The invention discloses a star catalogue intelligent system failure analysis method and system of a semi-supervised denoising auto-encoder, and relates to the technical field of fault detection. The method comprises the following steps: constructing a defect fault library of the star catalogue intelligent system according to the reason of the fault of the star catalogue intelligent system, and carrying out onhot coding on the fault state in the defect fault library; and receiving operation data of the star catalogue intelligent system in different states. According to the method, the advantages of supervised training and unsupervised training are combined, the accuracy and generalization ability of the model are improved by utilizing the accuracy of the marked data and the richness and low cost of the unmarked data and utilizing a large amount of unmarked data, and the original input data are damaged, so that the accuracy and generalization ability of the model are improved. More robust feature expression of nonlinear data can be completed through supervised training, and a Focal loss function is adopted, so that the phenomenon that the trained model shifts to a category with more samples due to imbalance between the samples can be avoided, and the model pays more attention to the category with less samples.

The invention relates to the technical field of camera on-orbit calibration, in particular to a fisheye camera on-orbit calibration method based on a starlight vector, which comprises the following steps of: S1, acquiring a plurality of star maps observed by a fisheye camera on orbit, and extracting and denoising star points to form a star point set; s2, according to fisheye imaging distortion distribution, a star point located in an imaging center area is selected from a star point set, and a starlight vector is constructed based on image point coordinates of the star point in combination with star catalogue data subjected to space-time deviation and propagation path deviation correction; and S3, performing local geometrical relationship star point matching on the starlight vector in the step S2. According to the method, the multiple star maps observed by the fisheye camera in orbit are obtained and processed to form the star point set, so that the problems of poor in-orbit calibration applicability and low precision caused by the fact that most traditional fisheye camera calibration methods adopt a ground pre-calibration or space reference object arrangement mode are solved.

The invention provides a star catalogue data matching method and device, computer equipment and a storage medium. The method comprises the steps of obtaining a plurality of star catalogue files; aiming at each star catalogue file, generating a target table corresponding to the star catalogue file, and storing serial number information of the celestial body data under multiple levels in the target table; constructing a storage calculation table according to the structure information of the target table and a set storage division strategy, and storing the table content of the target table into the storage calculation table; for any two to-be-matched star catalogue files, taking a column where a target hierarchy indicated by the storage division strategy is located as a connection key, carrying out connection operation on storage calculation tables corresponding to the two to-be-matched star catalogue files, and determining a matching result between multiple pieces of celestial body data with the same serial number information of the target hierarchy in the two storage calculation tables; and when the matching result is that matching succeeds, outputting at least part of data in the multiple pieces of celestial body data. According to the method, cross matching of celestial body data in different star catalogue files is realized, and the matching efficiency is improved.

The invention relates to the technical field of star catalogue cross identification, and provides a distributed cross identification method and device for massive star catalogues. The method comprises the following steps: dividing a celestial sphere surface into a plurality of blocks, and dividing all celestial bodies in a star catalogue into corresponding blocks according to mapping positions of the celestial bodies on the celestial sphere surface to form data partitions; performing cross identification on a first data partition in the first star catalogue, wherein the cross identification comprises the following steps: searching a second data partition matched with the first data partition in a second star catalogue; performing cross identification on each celestial body in the first data partition and each celestial body in the second data partition; the second data partition comprises a data partition located in the first block and a data partition located in a peripheral block of the first block in the second star catalogue; the first block is a block where the first data partition is located. Under the application scene of massive star catalogues, the data access times required by cross identification can be reduced, the cross identification efficiency can be improved, and the resource occupation can be reduced.

The invention provides an astronomical positioning navigation method based on optical observation, which comprises the following steps: screening and sorting observation targets to be observed according to initial conditions of a platform and ephemeris of the observation targets to serve as an observation task list; driving the optical telescope to steer and collect observation images according to the observation task list; matching astronomical images in the observation image with a fixed star catalogue so as to calculate observed celestial coordinates of each astronomical image; extracting a moving target as an observation target through star change of the multiple frames of observation images, and obtaining a motion track of the observation target; and carrying out platform position calculation. According to the astronomical positioning and navigation method disclosed by the invention, the attitude and position calculation of the platform is completed by integrating optical observation data of a fixed star and an observation target, and the autonomous navigation and positioning of the platform under the condition of no GNSS signal are realized.

This disclosure provides a method for segmenting a star catalog. The method includes: acquiring a target star catalog file corresponding to a target celestial sphere, the target star catalog file including observation data of M celestial bodies in the target celestial sphere; dividing the target celestial sphere into N sub-regions and N region numbers corresponding to the N sub-regions based on a predetermined maximum segmentation level K; determining the number of celestial bodies in each region represented by each of the N region numbers based on the observation data of the M celestial bodies in the target star catalog file, obtaining a result determining the number of N celestial bodies; and segmenting the target star catalog file according to the matching result between the result determining the number of N celestial bodies and a predetermined segmentation threshold T, determining multiple star catalog subset files corresponding to the target star catalog file. This disclosure also provides an apparatus, device, and storage medium for segmenting star catalogs.

The application discloses a small-sized separated penetrator for in-situ detection of celestial bodies, and relates to the technical field of penetrator equipment, comprising an aluminum honeycomb buffer module, which comprises an external protective shell and an aluminum honeycomb, and has the beneficial effects that the application is provided with in-situ detection of high-speed penetration of celestial bodies, and discloses a small-sized separated penetrator, which comprises a planet soil penetration module and a star table detection module, and realizes autonomous separation in the impact penetration process, the star table module can realize star table detection and communication with an orbiter, the penetration module is internally provided with an energy storage device and an impact hammer, and can continue to penetrate and dive relying on the energy storage device after impact; the star table module is connected with the penetration module through flexible wires, and can supply power and signal transmission to the latter, the technology enables the penetrator with the modular characteristic to have the in-situ detection capability of planet soil profile, aims to expand the application mode of the penetrator for celestial body detection, and provides a scientific basis for the research of star table structures.

The invention discloses a terrain autonomous sensing method for an extraterrestrial micro patrol detector, and belongs to the technical field of deep space detector control. According to the method, a Tof camera is adopted to measure an actual depth value of a star catalogue under camera coordinates, a depth theoretical model of a detection area is constructed, and a theoretical depth value of the star catalogue under the camera coordinates is calculated; designing an obstacle detection criterion based on the obtained actual depth value and the theoretical depth value; and detecting the obstacle in the detection area according to the obstacle detection criterion, and identifying whether the obstacle is a bulge or a pit. Aiming at the problem that a tiny patroller is difficult to realize effective perception under limited resources, obstacle detection only by using distance measurement information under an extremely low visual angle is realized, and the requirements of tasks such as star catalogue patrolling detection are met.

This invention designs a multi-scale star surface impact crater detection method, system, and medium. The method includes the following steps: S1: Acquire star surface images and segment them into image patches of different scales; S2: Construct multiple impact crater detection sub-models; S3: Train each sub-model using star surface image patches of different scales; S4: Input the segmented star surface image to be detected into each pre-trained sub-model to obtain the detection results; S5: Select the bounding boxes with high confidence and large area among all candidate bounding boxes of each impact crater as the final detection result for that impact crater. This invention can simultaneously identify impact craters of different scales in star surface images with high accuracy, especially improving the accuracy and efficiency of identifying small impact craters, providing more accurate and comprehensive data support for lunar science research, and promoting the in-depth development of lunar exploration and geological research.

The present invention relates to a method for collaborative obstacle avoidance for multi-node landers under non-uniform constraints, comprising: controlling the multi-node lander to descend to a preset altitude and acquiring an environmental map of a star catalog; calculating the trajectory of the multi-node lander's virtual center and the position of each node; determining the real-time distance of each node relative to the virtual center and calculating each node's own trajectory based on flexible transformation constraints such as the multi-node lander's configuration potential field, obstacle avoidance potential field, and collision avoidance potential field; and controlling each node to track its own trajectory to achieve collaborative obstacle avoidance. This method enables future asteroid probes to robustly and accurately adhere to landing sites of high scientific value during landing and sample return missions, and to cope with various hazardous terrains, such as steep slopes and narrow valleys.

The invention discloses a robot for detecting a narrow cave on a star catalogue, and belongs to the technical field of space robots. The defects that an existing star catalogue detection robot is large in size, complex in structure and incapable of adapting to narrow caves are overcome. The device comprises an advancing mechanism, a shell and a cave detection mechanism, and the shell is installed on the advancing mechanism and can be driven by the advancing mechanism to move; a mounting cabin is arranged at the front end of the shell, one end of the cave detection mechanism is mounted in the mounting cabin, the other end of the cave detection mechanism can extend out of or retract into the mounting cabin, and the cave detection mechanism can perform bending action so as to complete an omnidirectional detection task after the robot enters a narrow cave on a star catalogue. The method is mainly used for detecting the narrow caves on the star catalogue.

The present invention discloses a method, device and storage medium for calibrating the magnitude of a full-field instrument. The method is as follows: taking a star map, detecting and clustering the entire field of view to obtain a large number of bright spots; extracting observed stars, performing photometry and positioning on all bright spots to obtain the position, gray scale, uncertainty and zenith angle; matching the observed stars with a star catalog, and after successful matching, recording the following information, including the stellar magnitude, position, gray scale and uncertainty corresponding to the observed stars; dividing the full field of view into regions, counting all the stars that have been successfully matched in all frames within the region, fitting them by weighted least squares, and recording the zero points of the instrument magnitude obtained in different regions; performing polynomial interpolation on the zero points of the instrument magnitude in different regions of the full field of view to obtain the zero point correction at different fields of view; repeating the above steps at different time periods to obtain an accurate correction method for the on-orbit instrument magnitude of the full time period. The present invention can calibrate the on-orbit instrument magnitude of optoelectronic devices.

The present application relates to a kind of dark and weak target detection methods of wide-area astronomical image based on deep learning, belong to astronomical image processing technical field, including field of view division to original astronomical image, and pretreatment is carried out;Then the threshold segmentation label generation strategy based on star catalogue prior is established to generate label set;Deep learning semantic segmentation model is constructed and trained to obtain optimization model;With the astronomical image after pretreatment as input, output target segmentation map, and eliminate the connected domain target that does not conform to physical characteristics, based on the roundness feature of target area determination and separate fusion target, obtain the final mask of independent target;Based on final mask, the subpixel level center coordinates of each independent target are calculated using weighted centroid method, effectively improve the detection ability and measurement precision of low signal-to-noise ratio dark and weak target;While being able to adapt to the characteristics of astronomical data of high dynamic range, significantly improve target detection performance, especially in the extremely dark and weak target in signal-to-noise ratio 2 to 5 interval.

The application relates to a robot for exploring a narrow cave of a star table, belonging to the technical field of space robots. In order to solve the defects that the existing star table exploring robot is large in size, complex in structure and cannot adapt to narrow caves, the robot comprises a travelling mechanism, a shell and a cave exploring mechanism, the shell is installed on the travelling mechanism and can be driven to move by the travelling mechanism, the front end of the shell is provided with a mounting cabin, one end of the cave exploring mechanism is installed in the mounting cabin, the other end can be extended out of or retracted into the mounting cabin, and the cave exploring mechanism can perform a bending action to complete an omnidirectional exploration task after the robot enters the narrow cave of the star table. The robot is mainly used for exploring the narrow cave of the star table.

The invention belongs to the technical field of industrial automation, and particularly relates to a Healpix-based star catalogue homogenization segmentation and evaluation method. The method comprises the following steps: S1, acquiring original star catalogue data, and determining Healpix grid level parameters based on an expected subdivision degree of a user; s2, calculating a Healpix pixel index number of each celestial body by adopting a Healpix algorithm based on celestial sphere coordinates of each celestial body in a celestial sphere equator coordinate system contained in the original star catalogue data; s3, constructing a blank star catalogue, and constructing a homogenized star catalogue based on the celestial body set extracted by the sampling strategy and the Healpix pixel index number corresponding to each celestial body contained in the celestial body set; and S4, constructing a Uscore evaluation model, performing Uscore scoring on the homogenized star catalogue by using the Uscore evaluation model, and evaluating the uniformity of each celestial body in the homogenized star catalogue based on the Uscore score. According to the invention, an objective and quantifiable comparison reference is provided for the effects of different homogenization methods.

The invention discloses an embedded star catalogue data storage and query method oriented to a bare computer environment, relates to the technical field of embedded data query processing, solves the problem of mismatch between a DSP system structure and a star map query task in the prior art, and comprises the steps of star block storage, star block query, primary selection of star blocks in star block query and determination of navigation stars. In the star block storage, the GeoHash coding technology is adopted to take the star block as a primary key value, and a B + tree is adopted to store the star block in an easy-to-search form; a star map shot by an astronomical camera is preliminarily decomposed into primarily-selected star blocks in a partition mode, then corresponding storage star blocks in a bare computer environment are inquired respectively, and high flexibility and adaptability are achieved. The method is compatible with the GeoHash coding technology, parallel computing of a multi-core bare computer is facilitated, and the query speed can be doubled.

The present application discloses an electronic star finder for assisting the main telescope of an astronomical telescope to find target celestial bodies, which includes: an imaging unit, including an optical lens, for imaging a target sky area; an image sensor, which is arranged on the focal plane of the optical lens of the imaging unit, for sensing the image of the target sky area obtained by the imaging unit; and a calculation unit, which receives the image from the image sensor and is configured to perform the following processing based on the image: extracting star points in the image; and identifying the star points in the image by matching the star points with a star catalog database to obtain the names and / or equatorial coordinates of the star points. The present application also discloses an astronomical telescope including the above-mentioned electronic star finder, and an electronic star finding calculation device for use in cooperation with the electronic star finder. The electronic star finder of the present application is more convenient to operate and use compared with traditional optical star finders.

The invention discloses an astronomical identification calculation memory access optimization method for a CPU-DCU architecture, and the method comprises the steps: S1, carrying out the grid processing of the celestial body data of a to-be-identified star catalogue A and a to-be-identified star catalogue B, and recording the boundary information of each grid through the hierarchical vectorization of star catalogue-strip-grid; s2, dividing celestial body data in the star catalogue A and the star catalogue B into a plurality of transmission sub-tasks corresponding to each DCU by taking a stripe as a unit according to the maximum thread concurrency number of each DCU; s3, setting a calculation task of a single thread in the DCU; s4, setting a kernel function, and enabling each thread of the DCU to complete identification calculation by executing the kernel function; s5, performing identification calculation on celestial bodies in the star catalogue A and the star catalogue B by adopting the method in the step S4; according to the method, the memory access performance of astronomical gridding calculation on the DCU is improved while the calculation precision and integrity are guaranteed, and the overall calculation performance is improved.

The application provides a kind of based on ClickHouse column database's massive star table data fast merging method and system, through reducing the complexity of spherical distance calculation and using equidistant grid division index establishment method, the merging process of multi-band star table data is accelerated;The application is aimed at the application scene of astronomical cross identification and star table merging and the data processing demand of CSST high performance, low delay, research uses column database to complete the storage, retrieval and identification process of massive star table data, has good use value, has wide application scene in astronomical data processing field, also provides a new idea and direction for astronomical data processing.

The invention provides a fixed star map simulation method based on in-orbit measured data of a low-orbit moonlet, which comprises the following steps of: calculating orbit and attitude data of four corners of a star map CCD (Charge Coupled Device) according to row and column number interpolation of a to-be-simulated satellite star map image on the basis of satellite orbit, attitude and row time data measured in-orbit by the low-orbit moonlet in combination with a fixed star catalog; calculating right ascension and declination of angular points by combining internal and external orientation element information of a satellite, and selecting fixed star points falling into a star map in a star catalogue; the row and column numbers of the fixed star points in the star map are obtained by adopting a grid point bilinear interpolation method, and the gray scale information of the fixed star points is obtained by adopting a two-dimensional Gaussian distribution method. The star sky environment is further simulated by adding noise, and a simulation star map is output according to detailed information of result star points. According to the method, the simulation star map can be obtained quickly and efficiently, and the method has positive significance in improving the geometric calibration precision of the visible light load of the low-orbit moonlet through fixed star calibration.

The invention provides a star catalogue data merging method and device, computer equipment and a storage medium. The method comprises the steps of obtaining a target star catalogue file; according to right ascension and declination included in the celestial body data, determining serial number information of each piece of celestial body data under the target hierarchy, and dividing the celestial body data with the same serial number information in the target star catalogue file into the same data group to obtain a plurality of data groups; for each data group, determining an adjacent data group corresponding to the data group according to the number information corresponding to the data group; for each piece of celestial body data in the data group, determining a matching result between the celestial body data and other celestial body data in the data group, and a matching result between the celestial body data and each piece of celestial body data in the adjacent data group; and generating an index file corresponding to the target star catalogue file according to a matching result among the multiple pieces of celestial body data. According to the method, the whole table crossing and merging processing of the star catalogue file is realized, the number of repeated crossing times is reduced, and the star catalogue data crossing and merging efficiency is improved.

The invention discloses a satellite low-brightness design and analysis method based on a satellite thermal control model, and belongs to the technical field of satellites. The method comprises the steps of task analysis, star catalogue thermal control low-brightness design, satellite thermal control-brightness analysis integrated modeling, thermal control feasibility analysis, satellite brightness analysis based on a thermal control model, index satisfaction degree analysis and the like. At present, a theoretical calculation method of a simplified model is generally used for brightness analysis of a satellite, and can not be effectively iterated and updated in time according to a thermal control star catalogue design condition of the satellite. According to the design and analysis method, the thermal control design and the brightness design and analysis of the satellite are integrated, and the low-brightness design is realized while the thermal control design is performed; and establishing an analysis model with unified thermal control and brightness analysis, and carrying out statistical analysis of the satellite brightness based on thermal analysis model data. According to the method, the satellite low-brightness design and the thermal design are organically combined, and the efficiency and the accuracy of the brightness design are improved.

The star map recognition method based on radial features and interstellar angular distance relates to the field of star map recognition in astronomical navigation, solves the problems that the existing star map recognition algorithm has less number of stars to be recognized at one time, and the recognition speed and robustness are difficult to be compatible, and the method comprises the following steps: a navigation star table is made, radial recognition feature library and interstellar position relationship library are constructed according to the position distribution features of each navigation star and surrounding near neighbor stars; the interstellar position relationship library is used for storing the star number and radial ring number of the surrounding near neighbor stars of each navigation star; then, initial recognition and accurate recognition are carried out. In the process of matching by using the radial feature library, an angular distance error tolerance is set, and a weight value is set for each ring number, so that the star position noise has strong robustness. After the initial recognition, the accurate recognition is carried out, the surrounding near neighbor stars of the main star are used, and the method has strong robustness to false star noise and missing stars. The method realizes the recognition of multiple stars at one time, and improves the initial attitude solution accuracy.

The application discloses an astronomical cross-identification method for a heterogeneous many-core processor, and comprises the following steps: S1, obtaining the strip id of two star catalogs based on declination and the multi-node data distribution in strip units; S2, determining the number of heterogeneous many-core processors of each computing node and the maximum number of threads that can be simultaneously run by each heterogeneous many-core processor; S3, rearranging the star catalog data in each strip in strip units, and dividing the star catalog data into grids based on right ascension; S4, judging whether the right ascension span of each strip is too large during internal identification, so as to select the identification calculation of the CPU end in step S5 in a multi-thread parallel mode or the identification calculation on the heterogeneous many-core processor in step S6; S7, determining the identification selected result; and S8, obtaining the ID of a star body in two star catalogs respectively. The method can guarantee the calculation accuracy and integrity, improve the parallelism of the cross-identification algorithm and the use efficiency of the heterogeneous many-core processor, and realize the improvement of the overall calculation performance of the astronomical cross-identification.