A three-dimensional reconstruction method and system for shallow submarine strata topography

Abstract

The present invention relates to the field of intelligent surveying and mapping technology, and proposes a three-dimensional reconstruction method and system for submarine shallow stratum topography, which includes the following steps: obtaining the original data measured in the field by multiple sensors, and performing format conversion on the original data; the original data includes GPS data collected by a GNSS locator and shallow profile waveform data collected by a shallow profiler; performing preprocessing on the original data after format conversion in a two-dimensional view; performing three-dimensional reconstruction of a point cloud model according to the preprocessed original data, wherein the northing coordinate of the projection coordinate of the GPS data is used as the X coordinate, the easting coordinate of the projection coordinate of the GPS data is used as the Y coordinate, and the depth information of the shallow profile waveform data is used as the Z coordinate for three-dimensional reconstruction of the point cloud model, and then visualizing the point cloud model. The present invention can intuitively observe the three-dimensional geological conditions of the shallow stratum, which is beneficial to the marine shallow geology and marine engineering survey work.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent surveying and mapping, and more specifically, to a three-dimensional reconstruction method and system for submarine shallow stratum topography. Background Art

[0002] In submarine surveying and exploration in the field of intelligent underwater surveying and mapping, shallow stratum profiles have been widely used in marine shallow geology and marine engineering surveys, and their main measurement result is a shallow stratum profile diagram.

[0003] In marine shallow geology and marine engineering survey work, an unmanned ship mainly sails in a set navigation area according to a preset surveying and mapping route, samples the position information and depth information corresponding to each sampling point according to a preset frequency, and further generates a shallow stratum profile diagram of the navigation area through processing of the sampled data. However, the shallow stratum profile diagram is mainly a two-dimensional image, and it is difficult to intuitively describe the geological conditions of the shallow stratum, such as the sedimentary layer and the shallow stratum structure of the shallow stratum. Summary of the Invention

[0004] In order to overcome the defect that the shallow stratum profile diagram in the above-mentioned prior art is difficult to intuitively describe the geological conditions of the shallow stratum, the present invention provides a three-dimensional reconstruction method and system for submarine shallow stratum topography.

[0005] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0006] A three-dimensional reconstruction method for submarine shallow stratum topography, comprising the following steps:

[0007] Obtain the original data obtained from multi-sensor field measurement, and perform format conversion on the original data; the original data includes GPS data collected by a GNSS locator and shallow profile waveform data collected by a shallow profiler;

[0008] Preprocess the original data after format conversion in a two-dimensional view;

[0009] Perform three-dimensional reconstruction of a point cloud model according to the preprocessed original data, wherein the northing coordinate of the projected coordinate of the GPS data is used as the X coordinate, the easting coordinate of the projected coordinate of the GPS data is used as the Y coordinate, and the depth information of the shallow profile waveform data is used as the Z coordinate to perform three-dimensional reconstruction of the point cloud model, and then visualize the point cloud model.

[0010] As a preferred solution, the GPS data includes geodetic coordinate longitude and latitude data, projected coordinate easting coordinate, projected coordinate northing coordinate and time; the shallow profile waveform data includes intensity information and depth information of the waveform; the original data further includes draft data, SGY seismic data, three-dimensional attitude and inertial navigation data collected by an attitude instrument.

[0011] As a preferred solution, the step of converting the format of the original data includes: storing the original data according to the parameter types and positions of the data format according to the preset data format and the SGY seismic data format to achieve format conversion.

[0012] As a preferred solution, the preset data format includes a frame of original data composed of the geodetic coordinate longitude and latitude data collected by a GNSS locator, the east coordinate of the projected coordinate, the north coordinate of the projected coordinate, time, the intensity information and depth information of the shallow profile waveform collected by a shallow profiler, as well as the draft data and the flag bit of the data; among them, the shallow profile waveform data collected by the shallow profiler is stored in binary form; the SGY seismic data format includes a data file header and a data body, and the data file header includes the data sampling rate, the number of data sampling points per frame and the data sampling format; the data body includes the number of sampling points per frame, the sampling interval, the line number, time, the sampling unit, the coordinate information, the coordinate unit information and the sampling information.

[0013] As a preferred solution, the step of preprocessing the format-converted original data in a two-dimensional view includes: filtering the original data according to a preset wave intensity threshold; deleting noise points or unnecessary points in the original data by means of box selection; correcting the water depth data in the original data; and assigning 256 colors to each frame of the original data in the two-dimensional view to draw the formation line according to the waveform intensity of each frame of the original data.

[0014] As a preferred solution, when correcting the water depth data in the original data, a water depth correction algorithm such as a 5*5 median filtering method or a least squares method is used to correct the abnormal water depth.

[0015] As a preferred solution, preprocessing the format-converted original data in a two-dimensional view further includes: storing the original data, the formation line drawn after preprocessing, and the data flag bits corresponding to deleting the noise points or unnecessary points in the original data.

[0016] As a preferred solution, the step of three-dimensional reconstruction of the point cloud model according to the preprocessed original data includes: using the north coordinate of the projected coordinate of the GPS data as the X coordinate, using the east coordinate of the projected coordinate of the GPS data as the Y coordinate, and using the depth information of the shallow profile waveform data as the Z coordinate to construct the point cloud model; using the intensity information of the shallow profile waveform or the formation line data obtained after preprocessing as the normal vector to assign colors to the points in the point cloud model.

[0017] Furthermore, the present invention also proposes a three-dimensional reconstruction system for the submarine shallow stratum terrain, which applies the three-dimensional reconstruction method for the submarine shallow stratum terrain proposed in any of the above technical solutions. It includes a data reading module, a data format conversion module, a data preprocessing module, a three-dimensional reconstruction module and a display module.

[0018] Specifically, the data reading module is used to read the multi-sensor fusion data obtained by a shallow profiler, a GNSS locator, and an attitude instrument for performing field surveys as the original data; the data format conversion module is used to convert the format of the original data; the data preprocessing module is used to preprocess the original data in a two-dimensional view after format conversion; the 3D reconstruction module is used to perform 3D reconstruction of the point cloud model based on the preprocessed original data; the display module is used to visually display the 3D reconstructed point cloud model.

[0019] As a preferred solution, the system further includes a data storage module, which is used to store the original data, the formation lines drawn after preprocessing, and the data flag bit information corresponding to the noise points or unnecessary points deleted from the original data. The 3D reconstruction module performs 3D reconstruction of the point cloud model by reading the corresponding data from the data storage module.

[0020] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows: By reading the multi-sensor fusion data of a shallow profiler, a GNSS locator, an attitude instrument, etc. obtained from field surveys, first performing data preprocessing, and then performing 3D reconstruction of the shallow strata based on the GPS data and the shallow profile waveform data and then performing visualization processing, the 3D geological conditions of the shallow strata can be intuitively observed, which is beneficial to marine shallow geology and marine engineering survey work. Description of the Drawings

[0021] Figure 1 It is a flowchart of the 3D reconstruction method for the seabed shallow stratum topography in Embodiment 1.

[0022] Figure 2 It is a flowchart of the 3D reconstruction method for the seabed shallow stratum topography in Embodiment 2.

[0023] Figure 3 It is a two-dimensional view of the visualization result of the point cloud model in Embodiment 2.

[0024] Figure 4 It is a three-dimensional view of the visualization result of the point cloud model in Embodiment 2.

[0025] Figure 5 It is an architecture diagram of the 3D reconstruction system for the seabed shallow stratum topography in Embodiment 3. Detailed Embodiments

[0026] The drawings are only for illustrative purposes and should not be construed as a limitation of this patent;

[0027] To better illustrate this embodiment, some components in the drawings are omitted, enlarged, or reduced, which do not represent the dimensions of the actual product;

[0028] It is understandable that for those skilled in the art, some well-known structures and their descriptions in the drawings may be omitted.

[0029] The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments.

[0030] Embodiment 1

[0031] This embodiment proposes a three-dimensional reconstruction method for the shallow sub-bottom terrain, as Figure 1 shown, which is the flowchart of the three-dimensional reconstruction method for the shallow sub-bottom terrain of this embodiment.

[0032] The three-dimensional reconstruction method for the shallow sub-bottom terrain proposed in this embodiment includes the following steps:

[0033] S1. Obtain the original data obtained from multi-sensor field measurements, and perform format conversion on the original data.

[0034] In this embodiment, the original data obtained from multi-sensor field measurements includes GPS data collected by a GNSS locator, shallow profile waveform data collected by a shallow profiler, as well as draft data, SGY seismic data, three-dimensional attitude and inertial navigation data collected by an attitude instrument. That is, the original data is multi-sensor fusion data.

[0035] S2. Preprocess the original data in a two-dimensional view after format conversion.

[0036] In this embodiment, when preprocessing the original data, optionally perform operations such as filtering, removing noise points, correcting water depth, and drawing formation lines.

[0037] S3. Perform three-dimensional reconstruction of the point cloud model based on the preprocessed original data, where the northing coordinate of the projection coordinate of the GPS data is used as the X coordinate, the easting coordinate of the projection coordinate of the GPS data is used as the Y coordinate, and the depth information of the shallow profile waveform data is used as the Z coordinate for three-dimensional reconstruction of the point cloud model, and then visualize the point cloud model.

[0038] In the three-dimensional reconstruction, the three-dimensional reconstruction is mainly performed by fusing GPS data and shallow profile waveform data. Further, the reconstructed model is displayed, scaled, rotated, moved, etc. for intuitive viewing.

[0039] In this embodiment, by reading the multi-sensor fusion data of the shallow profiler, GNSS locator, attitude instrument, etc. obtained from field measurements, first perform data preprocessing, and then perform three-dimensional reconstruction of the shallow sub-bottom according to the GPS data and shallow profile waveform data and then perform visualization processing to obtain a point cloud model that can intuitively observe the three-dimensional geological conditions of the shallow sub-bottom.

[0040] Embodiment 2

[0041] This embodiment makes improvements on the basis of the three-dimensional reconstruction method of the seabed shallow stratum topography proposed in Embodiment 1.

[0042] This embodiment proposes a three-dimensional reconstruction method of the seabed shallow stratum topography, as Figure 2 shown, which is the flowchart of the three-dimensional reconstruction method of the seabed shallow stratum topography in this embodiment. It includes the following steps:

[0043] The three-dimensional reconstruction method of the seabed shallow stratum topography proposed in this embodiment includes the following steps:

[0044] S1. Obtain the original data obtained from multi-sensor field measurements, and perform format conversion on the original data.

[0045] The original data collected in this embodiment includes GPS data collected by a GNSS locator, shallow profile waveform data collected by a shallow profiler, as well as draft data, SGY seismic data, three-dimensional attitude and inertial navigation data collected by an attitude instrument.

[0046] Among them, the GPS data includes geodetic coordinate longitude and latitude data, projected coordinate east coordinate, projected coordinate north coordinate, and time.

[0047] The shallow profile waveform data includes intensity information and depth information of the waveform.

[0048] Furthermore, in this embodiment, according to the preset data format and the SGY seismic data format, the original data is stored according to the parameter type and position of the data format, realizing the format conversion of the original data.

[0049] Among them, the preset data format in this embodiment includes a frame of original data composed of geodetic coordinate longitude and latitude data, projected coordinate east coordinate, projected coordinate north coordinate, time collected by a GNSS locator, intensity information and depth information of the shallow profile waveform collected by a shallow profiler, as well as draft data and the flag bit of the data. Among them, the flag bit of the data represents the deletion and modification record of the data; the waveform data of the shallow profile waveform is stored in binary form.

[0050] The SGY seismic data format in this embodiment includes a data file header and a data body. The data file header includes data sampling rate (i.e., sampling interval), number of data sampling points per frame (i.e., the maximum number of sampling points per frame), and data sampling format (i.e., the encoding format of the data body); the data body includes the number of sampling points per frame, sampling interval, line number, time, sampling unit, coordinate information, coordinate unit information, and sampling information.

[0051] Furthermore, the conversion process is mainly to place the parameters in the corresponding positions. Among them, the conversion of the sampling information is to convert the waveform intensity of the shallow profile waveform into voltage (a sampling unit of SGY), and the formula is as follows:

[0052] Voltage = Intensity Information × 0.00061 - 0.125.

[0053] S2. Preprocess the original data in a two-dimensional view after format conversion.

[0054] In this embodiment, when preprocessing the original data, optionally perform operations such as filtering, removing noise points, correcting water depth, and drawing formation lines.

[0055] Among them, when filtering the original data, filter the original data according to a preset wave intensity threshold to remove the influence of wave intensity in some bands, such as echoes, etc.

[0056] In a specific embodiment, the waveform intensity range is 0 - 4096, and the default threshold for filtering is 1536 - 2560. If the filtering effect is not ideal, after restoring the data, reset the wave intensity threshold parameters according to the wave intensity distribution.

[0057] When removing noise points from the original data, remove the noise points or unnecessary points in the original data by means of box selection.

[0058] In a specific embodiment, in combination with the human-computer interaction module, select the deletion range by pressing the left mouse button and dragging. After releasing the mouse, the points within the range will be deleted, and at the same time, the database flag bit will also mark the corresponding waveform points, and store the data flag bit information with data deletion and modification records.

[0059] When correcting the water depth of the original data, correct the abnormal water depth through a water depth correction algorithm, including the correction of sudden water depth caused by fish schools or occlusion.

[0060] In a specific embodiment, use a water depth correction algorithm such as a 5*5 median filtering method or a least squares method to correct the abnormal water depth.

[0061] When drawing the formation line according to the original data, assign 256 colors to each frame of the original data in the two-dimensional view according to the waveform intensity of each frame of the original data to draw the formation line.

[0062] In this embodiment, each frame of the original data is displayed with 256 colors according to the size of the waveform intensity in the two-dimensional view. Users can draw the formation line according to different color displays and relevant geological knowledge during in-office processing, and store the drawn formation line data.

[0063] Furthermore, after preprocessing the original data after format conversion, store the original data, the formation line drawn after preprocessing, and the data flag bits corresponding to removing the noise points or unnecessary points in the original data in the database.

[0064] S3. Perform three-dimensional reconstruction of the point cloud model based on the preprocessed original data, where the northing coordinate of the projected coordinates of the GPS data is used as the X coordinate, the easting coordinate of the projected coordinates of the GPS data is used as the Y coordinate, and the depth information of the shallow profile waveform data is used as the Z coordinate for three-dimensional reconstruction of the point cloud model, and then the point cloud model is visualized.

[0065] In the specific implementation process, use the preprocessed original data or read relevant data from the database. Use the northing coordinate of the projected coordinates of the GPS data as the X coordinate, the easting coordinate of the projected coordinates of the GPS data as the Y coordinate, and the depth information of the shallow profile waveform data as the Z coordinate to construct a point cloud model; use the intensity information of the shallow profile waveform or the stratum line data obtained by preprocessing as the normal vector to assign colors to the points in the point cloud model.

[0066] Furthermore, perform point cloud visualization on the point cloud model, display, scale, rotate, move, etc. the point cloud model after three-dimensional reconstruction to facilitate intuitive viewing by the user. As Figure 3 、 4 shown, the two-dimensional view and three-dimensional view of the visualization result of the point cloud model in this embodiment.

[0067] In this embodiment, perform operations such as filtering processing, removing noise points, correcting water depth, and drawing stratum lines on the original data to obtain data with higher accuracy, then further perform three-dimensional reconstruction, and finally assign different colors according to different intensity values of each point in the point cloud model obtained by three-dimensional reconstruction or assign different colors according to the stratum line, so as to more intuitively observe the three-dimensional geological conditions of the shallow stratum.

[0068] Embodiment 3

[0069] This embodiment proposes a three-dimensional reconstruction system for the submarine shallow stratum topography, applying the three-dimensional reconstruction method for the submarine shallow stratum topography proposed in Embodiment 1 or 2. As Figure 5 shown, it is the architecture diagram of the three-dimensional reconstruction system for the submarine shallow stratum topography in this embodiment.

[0070] In the three-dimensional reconstruction system for the submarine shallow stratum topography proposed in this embodiment, it includes a data reading module 1, a data format conversion module 2, a data preprocessing module 3, a three-dimensional reconstruction module 4, and a display module 5.

[0071] Among them, the data reading module 1 is used to read the multi-sensor fusion data obtained by the shallow profiler, GNSS locator, and attitude instrument for field measurement as the original data.

[0072] The data format conversion module 2 is used to perform format conversion on the original data.

[0073] The data preprocessing module 3 is used to preprocess the original data after format conversion in a two-dimensional view.

[0074] The 3D reconstruction module 4 is used to perform 3D reconstruction of the point cloud model based on the preprocessed original data.

[0075] The display module 5 is used to visually display the point cloud model after 3D reconstruction.

[0076] Furthermore, it also includes a data storage module 6, which is used to store the original data, the formation lines drawn after preprocessing, and the data flag bit information corresponding to the noise points or unnecessary points deleted from the original data.

[0077] In the specific implementation process, the data reading module 1 reads multi-sensor fusion data such as GPS data, shallow profile waveform data, draft data, SGY seismic data, and three-dimensional attitude and inertial navigation data collected by the attitude instrument through wireless communication or wired communication with various sensors such as a shallow profiler, GNSS locator, and attitude instrument for performing field surveys.

[0078] Among them, the GPS data includes geodetic coordinate longitude and latitude data, projected coordinate east coordinate, projected coordinate north coordinate, and time; the shallow profile waveform data includes intensity information and depth information of the waveform.

[0079] The data reading module 1 transmits the read original data to the data format conversion module 2. The data format conversion module 2 stores the original data according to the preset data format and the SGY seismic data format according to the parameter types and positions of the data format, realizing format conversion. The data format conversion module 2 transmits the original data after format conversion to the data preprocessing module 3 for further processing, and at the same time transmits it to the data storage module 6 for storage.

[0080] Among them, the preset data format includes a frame of original data composed of geodetic coordinate longitude and latitude data, projected coordinate east coordinate, projected coordinate north coordinate, time collected by the GNSS locator, intensity information and depth information of the shallow profile waveform collected by the shallow profiler, as well as draft data and the flag bits of the data; among them, the shallow profile waveform data collected by the shallow profiler is stored in binary form.

[0081] The SGY seismic data format includes a data file header and a data body. The data file header includes data sampling rate, number of data sampling points per frame, and data sampling format; the data body includes the number of sampling points per frame, sampling interval, line number, time, sampling unit, coordinate information, coordinate unit information, and sampling information.

[0082] The data preprocessing module 3 includes a filtering processing unit, a noise point deletion unit, a water depth correction unit, and a formation line drawing unit.

[0083] Among them, the filtering processing unit filters the input original data according to a preset wave intensity threshold.

[0084] The noise point deletion unit deletes the noise points or unnecessary points in the input original data by means of frame selection.

[0085] The water depth correction unit corrects abnormal water depths in the input original data by using one of the water depth correction algorithms of 5*5 median filtering method and least squares method.

[0086] The formation line drawing unit assigns 256 colors to each frame of original data in a two-dimensional view to draw formation lines according to the waveform intensity in the data that has undergone filtering processing, noise point deletion, and water depth correction.

[0087] Further, after the noise point deletion unit completes the deletion of the noise points or unnecessary points in the original data, it stores the data flag bit information with data deletion and modification records in the data storage module 6; the formation line drawing unit stores the drawn formation line data in the data storage module 6.

[0088] The data preprocessing module 3 stores the preprocessed original data in the data storage module 6 and transmits it to the three-dimensional reconstruction module 4.

[0089] The three-dimensional reconstruction module 4 performs three-dimensional reconstruction of the point cloud model according to the data sent by the data preprocessing module 3 or the data read from the data storage module 6. Among them, the northing coordinate of the projection coordinate of the GPS data is used as the X coordinate, the northing coordinate of the projection coordinate of the GPS data is used as the X coordinate, the easting coordinate of the projection coordinate of the GPS data is used as the Y coordinate, and the depth information of the shallow profile waveform data is used as the Z coordinate to construct the point cloud model; the intensity information of the shallow profile waveform or the formation line data obtained by preprocessing is used as the normal vector to assign colors to the points in the point cloud model.

[0090] The three-dimensional reconstruction module 4 sends the point cloud model that has completed three-dimensional reconstruction to the display module 5, and the display module 5 visually displays the point cloud model.

[0091] The terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as a limitation of this patent;

[0092] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A three-dimensional reconstruction method for submarine shallow stratum topography, characterized in that, It includes the following steps: Obtain the original data obtained from multi-sensor field measurements, and perform format conversion on the original data; the original data includes GPS data collected by a GNSS locator, shallow profile waveform data collected by a shallow profiler, draft data, SGY seismic data, and three-dimensional attitude and inertial navigation data collected by an attitude instrument; the GPS data includes geodetic coordinate longitude and latitude data, projected coordinate east coordinate, projected coordinate north coordinate, and time; The shallow profile waveform data includes the intensity information and depth information of the waveform; The step of performing format conversion on the original data includes: According to the preset data format and the SGY seismic data format, store the original data according to the parameter type and position of the data format to achieve format conversion; Preprocess the original data after format conversion in a two-dimensional view, including: filtering the original data according to a preset wave intensity threshold; deleting noise points or unnecessary points in the original data by means of box selection. Specifically, in combination with the human-computer interaction module, drag the left mouse button to select the deletion range. After releasing the mouse, the points within the range will be deleted, and at the same time, the database flag bit will also mark the corresponding waveform points, and store the data flag bit information with data deletion and modification records; correct the water depth data in the original data; assign 256 colors to each frame of the original data in the two-dimensional view according to the waveform intensity of each frame of the original data to draw the formation line; Perform three-dimensional reconstruction of the point cloud model based on the preprocessed original data. Among them, use the projected coordinate north coordinate of the GPS data as the X coordinate, the projected coordinate east coordinate of the GPS data as the Y coordinate, and the depth information of the shallow profile waveform data as the Z coordinate to perform three-dimensional reconstruction of the point cloud model. Then, use the intensity information of the shallow profile waveform or the formation line data obtained after preprocessing as the normal vector to assign colors to the points in the point cloud model, and visualize the point cloud model.

2. The three-dimensional reconstruction method of the shallow subsea stratum topography according to claim 1, characterized in that The preset data format includes a frame of original data composed of geodetic coordinate longitude and latitude data, projected coordinate east coordinate, projected coordinate north coordinate, time collected by a GNSS locator, intensity information and depth information of the shallow profile waveform collected by a shallow profiler, draft data, and the flag bit of the data; among them, the shallow profile waveform data collected by the shallow profiler is stored in binary form; The SGY seismic data format includes a data file header and a data body. The data file header includes the data sampling rate, the number of data sampling points per frame, and the data sampling format; the data body includes the number of sampling points per frame, the sampling interval, the line number, the time, the sampling unit, the coordinate information, the coordinate unit information, and the sampling information.

3. The three-dimensional reconstruction method of the submarine shallow stratum topography according to claim 1, characterized in that When correcting the water depth data in the original data, use a water depth correction algorithm such as a 5*5 median filter method or a least squares method to correct abnormal water depths.

4. The three-dimensional reconstruction method of the shallow subsea stratum topography according to claim 1, wherein Preprocessing the original data after format conversion in a two-dimensional view also includes: storing the original data, the formation line drawn after preprocessing, and the data flag bit corresponding to deleting noise points or unnecessary points in the original data.

5. A three-dimensional reconstruction system for submarine shallow stratum topography, which applies the three-dimensional reconstruction method for submarine shallow stratum topography according to any one of claims 1 to 4, and is characterized in that, It includes: A data reading module, configured to read multi-sensor fusion data obtained by a shallow profiler, a GNSS locator, and an attitude instrument that perform field measurements as raw data; A data format conversion module, configured to perform format conversion on the raw data; A data preprocessing module, configured to preprocess the raw data that has undergone format conversion in a two-dimensional view; A three-dimensional reconstruction module, configured to perform three-dimensional reconstruction of a point cloud model based on the preprocessed raw data; A display module, configured to visually display the point cloud model that has undergone three-dimensional reconstruction.

6. The three-dimensional reconstruction system for the submarine shallow stratum topography according to claim 5, wherein The system further includes a data storage module, configured to store the raw data, the formation lines drawn after preprocessing, and the data flag bit information corresponding to removing noise points or unnecessary points in the raw data.

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