CN114863033A - Point cloud digital-analog-based section extraction method - Google Patents

Abstract

The invention discloses a cross section extraction method based on a point cloud digital model. The existing method for extracting the cross section by using the laser point cloud has low automatic processing degree and low efficiency. The method comprises the steps of constructing a PLY-format digital elevation model by using point cloud data; interpolating the acquired node coordinates of the section along the advancing direction of the section through a designated interval to obtain encrypted node coordinates, setting section extraction options and parameters, and interpolating the encrypted node elevation on the triangular surface of the digital elevation model by using a barycentric coordinate smooth interpolation algorithm to obtain the section; checking the section data by using the middle pile data, and thinning the section nodes; and finally, carrying out format conversion on the section data and drawing a section diagram. The software developed by the invention extracts the cross section by using the point cloud digital-analog under the CAD, and can finish the operations of cross section data extraction, check, thinning, format conversion and the like in one key after necessary data preparation and option parameter setting.

Description

Point cloud digital-analog-based section extraction method

Technical Field

The invention belongs to the technical field of surveying and mapping, and particularly relates to a cross section extraction method based on a point cloud digifax.

Background

The current stage of section data acquisition mainly adopts three modes of field manual actual measurement, interior industry aerial photography three-dimensional acquisition and laser radar point cloud extraction. The field manual actual measurement needs to run points at the characteristic position passed by the section, the working efficiency is low, the labor intensity is high, the safety risk of a complex and difficult area is high, and even the characteristic position cannot be reached. The interior industry aerial photography stereo collection relies on the visual measurement of operators on a digital measurement workstation to collect characteristic points, the plane precision of aerial photography stereo pairs cannot be corrected through field industry middle piles, and the problems of large workload, low automation degree, poor precision of vegetation coverage areas, low processing efficiency and the like exist. The laser radar point cloud extraction is a new technology, has the advantages of high efficiency, no contact, easy realization of automatic processing and the like, and is widely applied in recent years.

A common laser radar point cloud cross section extraction mode in the railway industry is to utilize LiDAR data processing software to complete point cloud classification, construct a digital elevation model after ground points are screened out, then import a line central line and a cross section line, manually click and select a cross section, input information such as a cross section name, a left offset distance, a right offset distance, a cross section node step length and the like, and output a cross section file pile by pile. And (3) when the vertical section is extracted, corresponding vertical pile elevation is interpolated based on LiDAR point cloud ground points according to the coordinates of the vertical pile points provided by the design profession, so that a vertical section three-dimensional coordinate point set is obtained. Although the method can extract the transverse and longitudinal sections, the problem that the extracted sections are inconsistent with the middle piles is not considered, and the conventional LiDAR data processing software is general software and has no open programming interface, so that the method cannot be deeply integrated with the line engineering section extraction service, the automatic processing degree is low, and the efficiency is not high.

Disclosure of Invention

In order to make up for the defects of the prior art, the invention provides the cross section extraction method based on the point cloud digifax, so that the railway design professional can autonomously acquire the required transverse and longitudinal sections through the point cloud digifax provided by the surveying and mapping professional, the survey result is quickly iterated, and the design process is accelerated.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a cross section extraction method based on a point cloud digifax specifically comprises the following steps:

s1: constructing a digital elevation model by using the point cloud data;

s2: acquiring a section name and a node plane coordinate;

s3: extracting a section by using a digital elevation model;

s4: checking section data;

s5: the nodes of the cross section are thinned;

s6: converting the section data format;

s7: and drawing a cross-sectional view.

Further, the step S1 specifically includes:

selecting airborne LiDAR ground points subjected to classification processing by point cloud data, wherein the data format is LAS; and constructing a digital model by utilizing a two-dimensional Dirony triangulation algorithm provided in a computational geometry algorithm library CGAL, and outputting a triangular network digital elevation model in a PLY format.

Further, the step S3 specifically includes:

and (4) interpolating the node coordinates of the cross section obtained in the step (S2) along the advancing direction of the cross section by a specified interval to obtain encrypted node coordinates, setting cross section extraction options and parameters, and interpolating the encrypted node elevation on the triangular surface of the digital elevation model by using a barycentric coordinate smooth interpolation algorithm to obtain the cross section.

Further, the step S4 specifically includes:

s4.1: when the level of a middle pile actually measured in field work is single in a target area, comparing the extracted section intersection point with the middle pile data of the same pile number of the level single, designating a horizontal distance and a height difference limit difference, when the distance between the section intersection point and the field middle pile point is within the horizontal distance limit difference, determining that the section intersection point and the field middle pile point are the same point, if the height difference is within the limit difference, replacing the interpolated node elevation with the field middle pile elevation, and otherwise, keeping the interpolated elevation and marking the section intersection point as the height difference overrun;

s4.2: outputting a middle pile replacement condition table, listing the difference value between the interpolation elevation and the field actual measurement elevation of the same point location, marking replacement and an overrun pile number, feeding back the overrun pile number to a point cloud digital analog manufacturing department for finding reasons, feeding back field inspection middle pile data if no problem exists, and finally obtaining the fault-free section data.

Further, the step S5 specifically includes:

setting the limit difference of the horizontal distance and the elevation difference between a certain section node and the front and rear nodes thereof, and controlling the thinning range; and only when the difference value of the distance between the point and the front point and the distance between the point and the rear point are within the limit difference and are not the horizontal and vertical intersection points, removing the node from the section data result, and otherwise, keeping the node.

The invention has the beneficial effects that:

1) the software developed by the invention extracts the section by using the point cloud digital-analog under the AutoCAD platform, and a user can finish the operations of section data extraction, check, thinning, format conversion and the like by one key after finishing necessary data preparation and option parameter setting, thereby improving the section extraction efficiency;

2) the invention can be fused with a circuit professional design software platform, and the circuit horizontal and vertical design result is directly used for a section extraction module to recover a circuit design model, so that the parametric extraction of a horizontal section and a vertical section is realized; the section extraction result is output as a cross section and a ground line format required by the line design, and the line design is assisted;

3) the invention realizes the input of the plane coordinates of the transverse and longitudinal sections in various modes, meets the use requirements of different specialties of railway survey design, can independently extract the required section results after obtaining the point cloud results provided by surveying and mapping specialties, reduces the mutual extraction of data, realizes quick iteration and accelerates the design process.

Drawings

FIG. 1 is a block flow diagram of the present invention:

FIG. 2 is a diagram of a key data structure used by the CGAL to generate a digital to analog model;

FIG. 3 is a schematic diagram of a barycentric coordinate smoothing interpolation algorithm adopted by the invention for extracting a section;

FIG. 4 is a land line format required for line specialization according to the present invention;

FIG. 5 is a cross-sectional format required for the circuit industry according to the present invention;

fig. 6 is a section format required by the tunnel speciality according to the present invention.

Detailed Description

The present invention will be described in detail with reference to specific embodiments.

As shown in fig. 1, the present invention specifically includes the following steps:

s1: and selecting ground point cloud data obtained through data processing links such as calibration, resolving, filtering, classifying and the like, wherein the data format is LAS, and the range of the required point cloud data can be determined through point cloud combined graph retrieval. And constructing a digital model by utilizing a two-dimensional Dirony triangulation algorithm provided in a computational geometry algorithm library CGAL, and outputting a triangular network digital elevation model in a PLY format. The Point cloud is stored in a Point set of Point _ set _3< Point _3> by reading ground Point cloud when constructing a digital analog, the Point set is traversed by a TIN structure and a two-dimensional Delaunay triangulation network is constructed, and finally the triangulation network is written into a PLY format by a binary file stream. The key data structure used by CGAL is shown in fig. 2.

S2: acquiring a section name and a node plane coordinate, wherein the three modes are respectively as follows:

1) the pattern mode is as follows: extracting information of lines and text labels drawn in a plan to obtain the information;

2) the parameter mode is as follows: setting parameters such as starting point mileage, end point mileage, section spacing, section left-right offset distance and the like of the line, and calculating through a line design model to obtain section node coordinates and pile number name labels;

3) text mode: and calculating to obtain the section node coordinates corresponding to the mileage stake marks through a line design model by using a text file containing the names of the appointed mileage stake marks and the left-right offset distance of the sections.

Lines and texts in the graphic mode are drawn by a designer according to professional requirements in combination with a plan view, and when the auxiliary line design or the sections required by the profession cannot be associated with the line model, the method is adopted, such as the sections of bridge longitudinals, culvert axes, tunnel inclined shafts, debris flow gullies for investigating adverse geological conditions and the like. Line node coordinates and text labels are obtained by calling functions under the ObjectARX software package autodesk. The linear Line type can directly obtain the coordinates of a starting point and an ending point through the readable and writable attributes StartPoint and EndPoint; the Polyline type can obtain the node coordinates of the designated sequence number through a GetPoint3dAt function; the single line of Text is obtained by its read-write attribute TextString, the multiple lines of Text by its read-only attribute Text.

And (3) directly recovering the line design model in the parameter mode and the text mode by importing data of a curve table and a broken link table (if broken links exist) in the line design result, and performing line mileage coordinate conversion through researched software after the model is recovered to solve the coordinates of each node of the target milepost number section. The line design model is implemented as an Access database file (format of mdb) or a group of text files (format of txt). The parameter mode is suitable for controlling whether the pile is added at the broken chain position or not through parameter options when the sections with fixed intervals in the appointed mileage paragraph need to be continuously obtained; the text mode is suitable for extracting a plurality of discontinuous mileage paragraph stake numbers.

The three input modes uniformly define the advancing direction of the line from a small mileage direction to a large mileage direction, and define the offset distance of the left section of the cross section in the advancing direction of the line as a negative value and the offset distance of the right section as a positive value.

S3: extracting a section by using a digital elevation model, firstly copying a digital-analog file of a required point cloud to a project engineering folder, dividing and encrypting the section nodes obtained in the step 2 at fixed intervals, successively using the encrypted section nodes as points P to be solved, solving barycentric coordinates (alpha, beta and gamma) corresponding to the points in a two-dimensional plane by using two-dimensional coordinates of the vertexes ABC of the triangle where the points P are located, and then solving the elevation of the points P by using the barycentric coordinates and the vertexes of the triangle, wherein a specific algorithm is shown in FIG. 3. And outputting the obtained three-dimensional coordinates of the nodes of the encrypted cross section and the offset distance between the nodes and the horizontal and vertical intersection points to obtain cross section data. If the vertical section is extracted, outputting the three-dimensional coordinates of the node of the encrypted section and the parallel distance between the node and the starting point along the line direction to obtain the data of the vertical section. In the present embodiment, the fixed pitch is 0.1 m.

S4: cross section data checking

In the railway line measurement stage, the centerline measurement is completed in the field by adopting a manual actual measurement mode such as a total station polar coordinate method, a GPS RTK method and the like, a horizontal single file containing a plane coordinate and an elevation of a center pile is obtained, and the horizontal single file is arranged into a text file only containing pile numbers and elevation data.

S4.1: setting a flat distance limit difference when extracting a cross section, wherein the limit difference is set to be 0.3m in the embodiment, when the flat distance between a section node and a middle pile point is within the limit difference, determining the section node and the middle pile point to be the same point position, comparing the difference between the actually measured field elevation data of the middle pile point corresponding to a horizontal single and the elevation data extracted by a digital-to-earth model of the section node, when the section node and the middle pile point are within the set limit difference, replacing a point cloud with the horizontal single elevation to extract an elevation value, and if the difference is greater than 0.5m, feeding back field verification according to the technical regulation requirements of satellite positioning and remote sensing measurement in railway engineering. Marking the replacement elevation, the pile number and the difference value which need to be fed back and checked, and outputting the pile number and the difference value to a middle pile replacement situation text file for reference;

s4.2: and listing the difference value between the interpolated elevation and the field actual measurement elevation of the same point location, marking a replacement and an overrun pile number, feeding back the overrun pile number to a point cloud digital analog manufacturing department for finding reasons, and feeding back field inspection pile data if no problem exists, and finally obtaining the error-free section data.

S5: in order to reserve all the topographic feature points as much as possible, the fixed spacing of the encrypted section nodes in the step S3 is set to be 0.1m, the extracted section data have more redundant points, and the section nodes are inconvenient to process when designed for professional use and need to be thinned;

in addition, some design professionally have a limit requirement on the maximum distance of the section nodes, so that in the example, the horizontal distance limit difference of 5m and the elevation limit difference of 0.2m are set during thinning. The specific algorithm is to control the thinning range by using the horizontal distance and the elevation difference between a certain section node and the front and rear nodes, and remove the node from the section data result only when the horizontal distance difference and the elevation difference between the certain section node and the front and rear nodes are within the limit difference and are not horizontal and vertical intersection points. If a horizontal and vertical intersection point exists when a vertical section is extracted, in order to ensure that the intersection point is not thinned, a text file containing an intersection point pile number is input, and judgment is carried out by calculating whether the distance between a target point and a starting point along the section direction is equal to the mileage difference from the intersection point to the starting point during thinning, so that the section node of the specified pile number is forcibly reserved. The cross section data obtained after thinning retains left and right end points and intersection points, and comprises all node offset distances and three-dimensional coordinate values (the intersection point is taken as the center, the offset distance on the left side is negative, and the right side is positive) from the left end point to the right end point according to the advancing direction of the line; the vertical section data is based on the starting point and comprises the offset distance from the starting point to all the nodes along the section line and the three-dimensional coordinate value of the nodes.

S6: and carrying out format conversion on the intermediate results of the section processed by the steps according to a professional design software interface. The ground line format of the traffic route selecting CAD system software for route design is shown in FIG. 4: the first row 2 indicates that the section data is two columns, the second and third rows indicate the pile numbers and the intersection point elevations of the two sections, and the last row is the end mark of the text data. The cross-sectional format is shown in fig. 5: the first row of marks 1 represents that the section data is absolute distance and absolute elevation, then intersection point pile numbers and elevations of all the cross sections, intersection points and elevations on the left side of the section, node ending marks '00' on the left side of the section, intersection points and elevations on the right side of the section are recorded in sequence, the node ending marks '00' on the right side of the section are recorded, and finally the file is marked to be ended by '0000'. The cross section format required by the tunnel profession is shown in fig. 6, all section data are sorted and stored into an Excel worksheet named as a ground line, each section comprises two rows of records, the first row of records stores the section name and the offset distance of each node, and the second row of records stores the elevation value of each node. The data interface required by the road profession is a cross-sectional and ground line format defined by the wefting road traffic aided design system software (HintCAD). The conversion of various professional interfaces among text formats is mainly completed through format arrangement after arithmetic operation, and the text format conversion Excel table is mainly used for processing an Excel worksheet by calling an API in Microsoft.

S7: and respectively storing the thinned horizontal and vertical section result data under a specified folder in a format of a text file, and then setting parameters such as a drawing data directory, a drawing scale, a table width and height, a section horizontal and vertical format, a layer, a color, a text style and the like to draw the section by using drawing tool software developed under an AutoCAD platform.

The invention is not limited to the examples, and any equivalent changes to the technical solution of the invention by a person skilled in the art after reading the description of the invention are covered by the claims of the invention.

Claims (5)

1. A cross section extraction method based on a point cloud digital model is characterized by comprising the following steps: the method specifically comprises the following steps:

s1: constructing a digital elevation model by using the point cloud data;

s2: acquiring a section name and a node plane coordinate;

s3: extracting a section by using a digital elevation model;

s4: checking section data;

s5: the nodes of the cross section are thinned;

s6: converting the section data format;

s7: and drawing a cross-sectional view.

2. The method for extracting the cross section based on the point cloud digital model as claimed in claim 1, wherein: the step S1 specifically includes:

selecting classified airborne LiDAR ground points from the point cloud data, wherein the data format is LAS; and constructing a digital model by utilizing a two-dimensional Dirony triangulation algorithm provided in a computational geometry algorithm library CGAL, and outputting a triangular network digital elevation model in a PLY format.

3. The method for extracting a cross section based on the point cloud digital model as claimed in claim 2, wherein: the step S3 specifically includes:

and (4) interpolating the section node coordinates obtained in the step (S2) along the section advancing direction through a specified interval to obtain encrypted node coordinates, setting section extraction options and parameters, and interpolating the encrypted node elevation on the triangular surface of the digital elevation model by using a barycentric smooth interpolation algorithm to obtain the section.

4. The method for extracting a cross section based on the point cloud digital model as claimed in claim 3, wherein: the step S4 specifically includes:

s4.1: when the level of a middle pile actually measured in field work is single in a target area, comparing the extracted section intersection point with the middle pile data of the same pile number of the level single, designating a horizontal distance and a height difference limit difference, when the distance between the section intersection point and the field middle pile point is within the horizontal distance limit difference, determining that the section intersection point and the field middle pile point are the same point, if the height difference is within the limit difference, replacing the interpolated node elevation with the field middle pile elevation, and otherwise, keeping the interpolated elevation and marking the section intersection point as the height difference overrun;

s4.2: outputting a middle pile replacement condition table, listing the difference value between the interpolation elevation and the field actual measurement elevation of the same point location, marking replacement and an overrun pile number, feeding back the overrun pile number to a point cloud digital analog manufacturing department for finding reasons, feeding back field inspection middle pile data if no problem exists, and finally obtaining the fault-free section data.

5. The method for extracting a cross section based on the point cloud digital model as claimed in claim 4, wherein: the step S5 specifically includes:

setting the limit difference of the horizontal distance and the elevation difference between a certain section node and the front and rear nodes thereof, and controlling the thinning range; and only when the difference value of the distance between the point and the front point and the distance between the point and the rear point are within the limit difference and are not the horizontal and vertical intersection points, removing the node from the section data result, and otherwise, keeping the node.

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