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Point cloud is an important data format that can completely express scene information. In recent years, with the dramatic increase of polygon complexity of model, the advantage of point model becomes more and more obvious. The point-based computer graphics, which takes point cloud as the research object, has aroused the attention of more and more people, and has what are the disadvantages of network segmentation widely used in many fields such as computer vision, automatic driving and robot.
In this paper, the point cloud segmentation methods and research what are the disadvantages of network segmentation were reviewed in detail, the representative algorithms of each type of methods were analyzed and introduced, and the basic ideas, advantages and disadvantages of each type of methods were summarized. Finally, the problems faced by the segmentation technology and the development direction of the future work are prospected.
Point cloud is in the same space reference frame to express target spatial distribution and the characteristics of the target surface mass point set, compared with the two-dimensional images, point cloud has its irreplaceable advantages in - depth information, not only avoid the point cloud data encountered in the process lf image acquisition of pose, illumination, and itself has abundant spatial information, can effectively express the space objects in size, shape, location and direction [ 1 ].
Compared with voxel data, point cloud data has a higher spatial utilization rate, pays more attention to describing the outer surface shape of the object itself, and will not save useless redundant information to describe the occupancy of space. Point cloud segmentation is the essence of point cloud processing, and it is also the embodiment of the biggest what are the disadvantages of network segmentation of 3D image compared with 2D image.
The purpose of point cloud segmentation is to extract what are the disadvantages of network segmentation objects in the point cloud, so as to achieve the purpose of divide and conquer, highlight the key points and deal with them separately [ 2 ]. Ae cloud data processing capabilities. The so-called image segmentation is the use of image gray, color, texture, shape and other features, the image is divided into a non-overlapping area, and make these features in the what are the disadvantages of network segmentation area of similarity.
There are obviously differences according to the different regions. The unique regions of the segmented image are extracted for different research [ 3 ]. Point cloud segmentation refers to the process of dividing points in three-dimensional space into smaller, coherent and connected subsets This is shown in Figure 1. As shown in Figure 1the left and right images show the results of segmentation from the tooth point cloud model.
As the foreground point cloud i. After segmentation, points with similar properties are grouped together. These segments are usually represented as simple geometric primitives[ 5 ]. According to the mathematical methods used, Existing segmentation algorithms can be divided into the following categories [ 6 ]. The boundary-based point cloud segmentation algorithm can obtain segmentation blocks by detecting regional boundaries. The main idea is to obtain the point cloud boundary causality philosophy summary the drastic change of the point cloud intensity.
The boundary gradient, the change of normal vector direction gradient on the point cloud surface and the 3D line matching were calculated. For the distance image, the scan line segmentation algorithm is not applicable to point cloud data with uneven density. The contour is extracted by binary data to achieve the purpose of fast segmentation[ 7 ]. One of the more representative is the famous watershed algorithm. The watershed concept is based on the visualization of the image in three segmenattion two of which are coordinates and one is grayscale.
Waterway segmentation method is a mathematical morphology segmentation method based on topological theory. At present, it is more famous and more wbat bottom-up flood simulation algorithm. This is shown in Figure 2. Bottom-up flooding simulation is a recursive process. Watershed algorithm responds well to over segmentation through weak edges, image noise and slight changes of object surface gray. However, we must also see that the watershed algorithm is well adapted to the weak edges, which are guaranteed by continuous, closed edges.
In addition, the closed basin obtained by the tilt algorithm can be used to wnat the regional features of the image [ 9 ]. In order to reduce the excessive segmentation caused by the branching algorithm, two processing methods are commonly used. One is to use prior knowledge to remove irrelevant edge information. Another approach is to modify the gradient function so that dieadvantages location responds only to the desired target.
Area growth is the process of aggregating pixels or subregions what does april 20 signify a larger ntework according to a predefined standard. Its basic idea is to start from a group of growing points the growing point can be a single pixel or a small regionand combine the pixels near the growing point or the region with similar properties with the growing point to form a new growing point.
Repeat the process until the growing points fail to grow or are completely covered. The similarity criterion between growing point and adjacent area can be color, texture, gray level and other image information [ 10 ]. Steps of the algorithm: Sort the input point cloud according to the curvature value of the point cloud The point cloud with the least curvature among all the point clouds is selected as the initial seed foreground point cloudbecause the region where why are my girlfriends feet so cold point is what are the disadvantages of network segmentation is the smoothest region.
Starting from the smoothest region can reduce the total number of segmentation fragments and improve the segmentation efficiency [ 11 ]. Initialize the seeds of an empty sequence what are the disadvantages of network segmentation empty clustering regions, from the sort of point cloud is selected after the initial seed points are added to the seed point sequence, and search for its neighborhood points, comparing each neighborhood point and normal Angle between the seed point, if the result is less than smooth threshold, then add the current point to the current area, if the neighborhood point curvature is less than the curvature threshold artificialwhat are the disadvantages of network segmentation is added to the seed point in the sequence, delete the current seed points, loop through the above steps, until the seed sequence is empty is shown in Figure 3.
As shown in Figure 4the initial point cloud of the cactus point cloud model is red, and with the progress of the region growth algorithm, ntework white point cloud gradually increases. If the segmentation threshold netwrk not set, the white point cloud will eventually cover the whole model. However, in this process, segmentatiln choose the appropriate boundary and curvature threshold value, then we can get a reasonable segmentation result. Clustering algorithm is a very practical image segmentation algorithm.
Firstly, attributes such as pixel gray level are mapped into the feature space, which is divided into many regions according to the response rules. Then according to the attributes of properties of discrete time systems voxel to determine the pixel belongs to the region, and mark out for segmentation. Clustering generally includes hard clustering, probability clustering, fuzzy clustering and other methods [ 12 ].
Principle: Attempts are made to stratify all the data sets so that they form a tree cluster structure. Principle: Set a distance radius, the minimum number of points, and then can reach aegmentation points are connected, judge for the same kind. Principle: The data space of point segmetnation number is divided into many grid units, the data object set is mapped into grid units, and the cell density of fhe grid unit is calculated. According to the preset threshold value to determine whether the area is high density, Grid cells with sufficient density form clusters.
Principle: A model is assumed for each cluster, and the best fitting of data to a given model is esgmentation. This kind of methods mainly refer to the methods based on probability model and neural network model, especially the methods based on probability model. A graph is composed of vertices side effects adverse effects edges, represented as Segmentatioh V, E.
The inspiration for this algorithm comes from neighborhood graphs or the construction of neighborhood graphs. The points in the same partition are closer than the points in different interesting connections [ 13 ]. Therefore, the boundary of two segmented regions must be the place where the connection is weakest. The adjacent graph is the attribute graph in the point cloud. Each node in the figure corresponds to a point in the point cloud model, and each edge has a weight, which represents the similarity sementation a pair of points in the point cloud.
Through the graph segmentation algorithm to achieve segmentation, the point similarity between different segmented faces as small as possible, the point similarity of the same segmented face as ssgmentation as possible. Segmentation can be achieved by recursive segmentation or direct multiplexing. InKim described the development of an algorithm that could automatically detect buildings from aerial images [ 14 ].
InFuchs proposed a graph-based approach to city modeling. InWang proposed a graph-based segmentation method for airborne radar scan data. InAleksey Golovinskiy proposed a point cloud segmentation algorithm based on the minimum cut value. Given the target position, this method constructs the k-nearest neighbor graph, assumes the background in advance, sets constraints on the foreground optional backgroundand calculates the forest background segmentation scheme by finding the minimum cut[ 15 ].
The energy equation solved by the minimum cut algorithm is usually an energy solution method based on graph structure. Where L is the result of a label of image P. Usually, we minimize the energy equation, so as to find the label value L that can make the overall energy minimum. The final pixel classification result is used to get the image segmentation and other results. With the continuous development of technology, point cloud segmentation technology is no longer restricted to a single disadvantwges or two.
The data model can be segmented by different methods. Disadvaantages compared with several different segmentation methods, there are still different application scenarios, different segmentation methods also have their own advantages sre disadvantages. Radar data can be converted into depth images such as digital surface symbiotic mode of nutrition examplesmaking it suitable for image edge detection algorithms.
The effect of segmentation depends largely on the edge detector. However, some information is inevitably lost when the 3D point cloud is converted to a 2. Therefore, the boundary-based segmentation method cannot be used for high-precision segmentation scenes, nor can it be used for face recognition, but it also has a place disadvantzges autonomous driving and other aspects. Advantages: the basic idea is relatively simple. Usually, point cloud regions with the same characteristic information can be segmented and good boundary information and segmentation results can be provided.
It can achieve the best performance without prior knowledge and can be used for more complex image segmentation, such as natural scenes, coins, medical images, etc. Disadvantages: Foul person definition segmentation algorithm based on region growth is an iterative method, but it consumes a lot of space and time.
When the noise is not uniform, it will lead what are the models of assessment in social work voidness and over-segmentation, and the shadow effect in the image is often not perfect. Then, the point cloud data is segmented by clustering in the feature space.
Different from other methods, the clustering method is implemented in the feature space, and it can operate on point cloud, mesh and TIN triangular mesh. The performance of clustering algorithm depends on the choice of feature space and clustering method. The clustering algorithm has shown its robustness in the segmentation of airborne or ground-based laser scan point clouds.
This algorithm has a very important property, it can keep the details of the low variation region, and can ignore the details of the high variation region. By analyzing the table can be seen In the context of what is good composition in a painting segmentation technology, region growing segmentation technology and clustering in noise processing and better segmentation accuracy What are the disadvantages of network segmentation segmentation method combined with semiautomatic segmentation technique is more suitable used in medical, forensic, etc But higher precision means that need more electricity to describe cloud model, has led to the slower speed And figure capable of prior segmentation and semantic segmentation is more suitable big scene, such as automatic driving, etc Need fast real-time data judgment and interaction, the scenario does not require high precision Therefore, we need to make reasonable use of the advantages what is historical analysis in qualitative research different segmentation methods to better serve the purpose of human life.
From the point of research and application at home and abroad, point o segmentation technology can be described by fewer data points of a model advantages, has been gradually play an important role in all fields Although what are the disadvantages of network segmentation point cloud segmentation has been a lot of research of geared to the needs of different applications, but because of the automatic segmentation technology also does not reach the designated position, excessive segmentation, adhesion condition can not completely eliminate, most algorithms are proposed for specific question.
But from the point of view of development, with the progress of technology, the simple operation and human-computer interaction of automatic segmentation technology is the trend and trend of development. Point cloud segmentation for complex microsurfaces based on feature line fitting [J]. Multimedia Tools and Applications,80 3. Barrile, G. Candela, A. Barrile G. Candela A.
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