CN117911626B - Building boundary polygon construction method and system based on laser point cloud data - Google Patents
Building boundary polygon construction method and system based on laser point cloud data Download PDFInfo
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Abstract
The invention discloses a building boundary polygon construction method and system based on laser point cloud data, and belongs to the technical field of space big data processing. The method comprises the following steps: s1, acquiring point cloud data, and calculating a buffer area radius and a buffer area fusion polygon based on the point cloud data; s2, extracting building polygon vertexes based on the buffer zone fusion polygon and the buffer zone radius to obtain a vertex set; and S3, based on the vertex set, sequentially generating an outer ring polygon and an inner ring polygon, and based on the outer ring polygon and the inner ring polygon, obtaining a building boundary polygon. The method for constructing the building polygon provided by the invention selects the proper buffer radius parameter by using a trial-and-error method, can reduce the influence of artificial subjective factors, has simple method for extracting the building polygon vertex and generating the polygon, is easy to realize, and can adapt to the point cloud data processing of the buildings with various forms.
Description
Technical Field
The invention belongs to the technical field of space big data processing, and particularly relates to a building boundary polygon construction method and system based on laser point cloud data.
Background
With the wide application of laser scanning equipment and data processing technology thereof in mapping service, the acquisition rate and the number of spatial data are greatly improved. In the process of "digital city" construction, the extraction of building geometry (or building polygons) from laser point cloud data (point cloud data for short) is the most common and very important work link. The building extracted from the building point cloud data as shown in fig. 1 is a polygon as shown in fig. 2.
Currently, the technical route for constructing a building boundary polygon by using point clouds is as follows: firstly, building point cloud data are segmented/classified according to the point cloud data, and then boundary polygons are constructed from the building point cloud data. The research of the point cloud data segmentation/classification technology is mature and has been widely used. Building boundary polygon techniques from segmented point cloud data have also received attention from many scholars and companies, creating a series of building algorithms and geographic information system tools.
The technology of constructing building boundary polygons by using point cloud data is inherited by point set data enveloping polygon algorithms, and the enveloping polygon generating algorithms mainly comprise enveloping rectangles (or orthogonal minimum circumscribed rectangles), minimum constraint rectangles, convex shells (convex polygons) and the like. Because of the wide variety of building shapes, these algorithms are difficult to adapt to irregularly shaped buildings, especially buildings that are not adapted for concave-polygon shapes. For this reason, many scholars propose a method for extracting building contour lines based on point cloud data of α -shape (α -graph), which can be adapted to the extraction of multi-shape building boundary polygons to a certain extent. Currently, some tools for extracting building contour lines from point cloud data provided by geographic information system software can also achieve the purpose of extracting building boundary polygons through a large number of manual interaction operations. For example, the point cloud data processing tool provided by arcgipro software needs to rasterize building point cloud data to generate a raster image, and then uses the "raster turn-plane" tool provided by the software to convert the building raster data into polygons.
The existing technology for extracting the building boundary polygon from the point cloud data is mainly to expand an alpha-shape algorithm, and the alpha-shape algorithm is complex, so that the program is difficult to realize, and the alpha value is difficult to determine in practical operation, so that the existing technology for constructing the building boundary polygon by the point cloud has more defects. Although some geographic information system software also provides corresponding tools, the tools need to be subjected to complex manual interaction operation, and point cloud rasterization is needed to be converted into polygons, so that the operation is complex.
Disclosure of Invention
The invention aims to solve the defects of the prior art, and provides a building boundary polygon construction method and system based on laser point cloud data. The algorithm is simple and easy to realize, and can adapt to the construction of polygons of buildings with various forms.
In order to achieve the above object, the present invention provides the following solutions: the building boundary polygon construction method based on laser point cloud data comprises the following steps:
s1, acquiring point cloud data, and calculating a buffer area radius and a buffer area fusion polygon based on the point cloud data;
s2, extracting building polygon vertexes based on the buffer zone fusion polygon and the buffer zone radius to obtain a vertex set;
and S3, based on the vertex set, sequentially generating an outer ring polygon and an inner ring polygon, and based on the outer ring polygon and the inner ring polygon, obtaining a building boundary polygon.
Further preferably, S1 comprises:
S11, acquiring the point cloud data, and extracting a preset number of the point cloud data to serve as first point cloud data;
S12, calculating the average value of the nearest neighbor distance of the first point cloud data, and calculating a buffer polygon of each point of the point cloud data by taking the average value as an initial buffer radius; merging the buffer area polygons to obtain a merged polygon;
s13, judging whether the fusion polygon covers a single polygon of all the point cloud data, if not, increasing the radius of the initial buffer area by a preset distance, and recalculating the buffer area polygon of each point of the point cloud data; merging the buffer area polygons to obtain a merged polygon; and performing recursive calculation until the fusion polygon covers all the point cloud data and is a single polygon, and obtaining the final buffer fusion polygon and the final buffer radius.
Further preferably, S2 comprises:
S21, extracting an outer ring of the final buffer zone fusion polygon, generating an outer ring polygon, and calculating an inward contraction buffer zone polygon with a radius which is increased by a preset distance by the final buffer zone radius;
s22, extracting all points outside the inward contraction buffer zone polygon in the point cloud data, and forming an outer ring polygon vertex set of the building from the external points;
S23, judging whether the inward contraction buffer area polygon is a simple polygon, if so, the building outer ring polygon vertex set is a building boundary polygon vertex set; if not, sequentially extracting inner rings of the inward contraction buffer zone polygons, searching points contained in the inner ring buffer zone with the preset distance as a radius, and forming an inner ring polygon vertex set.
Further preferably, S3 includes:
S31, searching the vertex of the polygon in the inward contraction buffer area closest to each point of the polygon vertex set of the outer ring of the building, and assigning a value to the polygon vertex of the outer ring of the building based on the serial number of the vertex; sequentially connecting the assigned vertices of the outer ring polygon of the building according to assignment sequence numbers from small to large to generate an outer polygon of the building;
S32, when the inner ring polygon vertex set is an empty set, the building outer polygon is the building boundary polygon; s31, when the inner ring polygon vertex set is not an empty set, performing a step S31 on each point of the inner ring polygon vertex set to generate a polygon inside a building;
S33, removing the building inner polygon from the building outer polygon to obtain the building boundary polygon.
The invention also provides a building boundary polygon construction system based on laser point cloud data, comprising: the device comprises an acquisition module, an extraction module and a generation module;
the acquisition module is used for acquiring point cloud data and calculating a buffer area radius and a buffer area fusion polygon based on the point cloud data;
the extraction module is used for extracting building polygon vertexes based on the buffer zone fusion polygons and the buffer zone radius to obtain vertex sets;
The generating module is used for sequentially generating an outer ring polygon and an inner ring polygon based on the vertex set, and obtaining a building boundary polygon based on the outer ring polygon and the inner ring polygon.
Further preferably, the acquiring module includes: the device comprises an extraction unit, a calculation unit and a circulation unit;
the extraction unit is used for acquiring the point cloud data and extracting a preset number of the point cloud data to serve as first point cloud data;
the computing unit is used for computing a mean value of nearest neighbor distances of the first point cloud data, and computing a buffer polygon of each point of the point cloud data by taking the mean value as an initial buffer radius; merging the buffer area polygons to obtain a merged polygon;
The circulating unit is used for judging whether the fusion polygon covers all the point cloud data and is a single polygon, if not, increasing the radius of the initial buffer area by a preset distance, and recalculating the buffer area polygon of each point of the point cloud data; merging the buffer area polygons to obtain a merged polygon; and performing recursive calculation until the fusion polygon covers all the point cloud data and is a single polygon, and obtaining the final buffer fusion polygon and the final buffer radius.
Further preferably, the extraction module includes: an outer ring extraction unit, a vertex extraction unit and a judgment unit;
The outer ring extraction unit is used for extracting the outer ring of the final buffer zone fusion polygon, generating an outer ring polygon, and calculating an inward contraction buffer zone polygon with the radius of the final buffer zone increased by a preset distance as the radius;
The vertex extraction unit is used for extracting all points outside the inward contraction buffer zone polygon in the point cloud data, and forming an outer ring polygon vertex set of the building from the external points;
The judging unit is used for judging whether the inward contraction buffer polygon is a simple polygon or not, and if so, the polygon vertex set of the outer ring of the building is a polygon vertex set of the boundary of the building; if not, sequentially extracting inner rings of the inward contraction buffer zone polygons, searching points contained in the inner ring buffer zone with the preset distance as a radius, and forming an inner ring polygon vertex set.
Further preferably, the generating module includes: an external polygon generating unit, an internal polygon generating unit, and a building polygon generating unit;
The external polygon generation unit is used for searching the vertex of the inward contraction buffer polygon closest to each point of the polygon vertex set of the outer ring of the building, and assigning a value to the polygon vertex of the outer ring of the building based on the serial number of the vertex; sequentially connecting the assigned vertices of the outer ring polygon of the building according to assignment sequence numbers from small to large to generate an outer polygon of the building;
When the internal polygon generating unit judges that the inner ring polygon vertex set is an empty set, the building external polygon is the building boundary polygon; when the inner ring polygon vertex set is not an empty set, generating a polygon inside a building according to the points in the inner ring polygon vertex set and the working process of the external polygon generating unit;
The building polygon generation unit is used for removing the building interior polygon from the building exterior polygon to obtain the building boundary polygon.
Compared with the prior art, the invention has the beneficial effects that:
The method for constructing the building polygon provided by the invention selects the proper buffer radius parameters by using a trial-and-error method, can reduce the influence of human subjective factors, has simple method for extracting the building polygon vertexes and generating the polygon, is easy to realize, and can adapt to the point cloud data processing of the buildings with various forms.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the embodiments are briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic view of building point cloud data according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a polygon structure of a building boundary extracted using the prior art;
FIG. 3 is a schematic flow chart of a method for extracting a boundary polygon of a building according to the present invention;
FIG. 4 is a schematic diagram of a buffer;
FIG. 4 (a) is a schematic diagram of a single-point buffer; FIG. 4 (b) is a schematic diagram of a multi-point fusion buffer;
FIG. 5 is a schematic diagram of a single polygon;
Wherein FIG. 5 (a) is a single polygon schematic without an inner ring; FIG. 5 (b) is a single polygon schematic with an inner ring;
FIG. 6 is a schematic illustration of an inwardly contracted buffer polygon;
FIG. 6 (a) is a schematic diagram of an original polygon; fig. 6 (b) is a schematic diagram of an inwardly contracted buffer polygon.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Embodiment one:
the embodiment provides a building boundary polygon construction method based on laser point cloud data, as shown in fig. 3, comprising the following steps:
S1, acquiring point cloud data, and calculating a buffer zone fusion polygon and a buffer zone radius based on the point cloud data.
In this embodiment, a trial and error method is used to estimate the appropriate buffer radius. Specifically, S1 includes:
s11, acquiring point cloud data, and extracting a predetermined number of point cloud data to serve as first point cloud data.
In this embodiment, the point cloud data D shown in fig. 1 is used for calculation, and a random number generating function is used to randomly extract a certain amount of point cloud data.
S12, calculating a mean value d_avg of the nearest neighbor distance of the first point cloud data by using a distance sorting method, taking the mean value d_avg as an initial buffer radius r, and calculating a buffer polygon of each point of the point cloud data D by using a buffer function; merging the buffer polygons to obtain a merged polygon B.
Wherein the nearest neighbor distance is the planar geometric distance from the target point to its nearest point. The buffer area is a space point set with the target point smaller than or equal to the specified radius; thus, the buffer of points is a circle, as shown in FIG. 4 (a); in the field of information systems, the boundary line of a circle is expressed as a series of ordered sets of vertices. The fused polygon B of the buffer is a polygon obtained by merging buffers of all point cloud data, as shown in fig. 4 (B).
S13, judging whether the fusion polygon B covers all point clouds and is a single polygon, if not, increasing the initial buffer radius r by a preset distance delta d, and recalculating the buffer polygon of each point of the point cloud data; merging the buffer area polygons to obtain a merged polygon B; and performing recursive calculation until the fusion polygon B covers all point cloud data and is a single polygon, and obtaining a final buffer fusion polygon B and a final buffer radius r (namely r=r+m delta d, m is the increasing number).
Wherein a single polygon is a single complete, non-segmented polygon, as shown in fig. 5. A single polygon may contain multiple inner rings as shown in fig. 5 (b).
And S2, extracting building polygon vertexes based on the buffer zone fusion polygons and the buffer zone radius to obtain a vertex set.
S2 comprises the following steps:
s21, extracting an outer ring of the final buffer zone fusion polygon B, generating an outer ring polygon R', and calculating an inward contraction buffer zone polygon R with a preset distance (r+Deltad) of the radius increase of the final buffer zone as a radius.
Wherein the outer ring is a boundary between the polygonal inner space and the outer space, i.e., an outermost boundary. The inward contraction buffer zone is a polygonal buffer zone with a radius of a negative value, and represents an inner area with a distance from a polygonal boundary line being smaller than or equal to the buffer radius; as shown in fig. 6.
S22, extracting all points outside the inward contraction buffer polygon R in the point cloud data D, and forming the external points into a building outer ring polygon vertex set P.
S23, judging whether the inward contraction buffer zone polygon R is a simple polygon or not, if so, taking the building outer ring polygon vertex set P as a building boundary polygon vertex set; if not, sequentially extracting the inner ring C of the inward contraction buffer polygon R, searching the points contained in the inner ring buffer with the preset distance delta d as the radius, and forming an inner ring polygon vertex set.
The vertex sets extracted by all inner ring buffers of inward contraction buffer polygon R form all inner ring polygon vertex sets of the building, expressed as: e=e 1∪E2∪...∪En, where E i is the i-th set of polygon vertices of the building inner ring and n is the number of inner rings.
Wherein the simple polygon is a single polygon without an inner ring, as shown in fig. 5 (a).
And S3, sequentially generating an outer ring polygon and an inner ring polygon based on the vertex set, and obtaining a building boundary polygon based on the outer ring polygon and the inner ring polygon.
S3 comprises the following steps:
S31, searching the vertex q of the inward contraction buffer polygon R closest to the point P in the polygon vertex set P of the outer ring of the building, and assigning the polygon vertex P of the outer ring of the building based on the sequence number of the vertex q (namely, assigning the sequence number of q to P); all points of the assigned P are sequentially connected from small to large according to the assigned sequence numbers to form a closed multi-sense line, and the closed multi-sense line is converted to generate a polygon M outside the building.
All vertexes of the polygon have a serial number, and the connection method is to sequentially connect the vertexes along the edge line in a anticlockwise manner from one vertex.
S32, when the inner ring polygon vertex set E is an empty set, the building outer polygon M is a building boundary polygon; and when the inner ring polygon vertex set E is not an empty set, performing S31 step on the points of each subset of the inner ring polygon vertex set E to generate a polygon inside the building, wherein the polygon is expressed as: n= { N 1,N2,...,Nn }, where N i is the ith inner ring polygon of the building and N is the number of inner rings.
S33, removing (subtracting operation) the building interior polygon from the building exterior polygon to obtain the building boundary polygon.
Embodiment two:
The present embodiment provides a building boundary polygon construction system based on laser point cloud data, including: the device comprises an acquisition module, an extraction module and a generation module.
The acquisition module is used for acquiring point cloud data and calculating a buffer zone fusion polygon and a buffer zone radius based on the point cloud data.
In this embodiment, the acquisition module estimates the appropriate buffer radius using a trial and error method. Wherein the acquisition module comprises: the device comprises an extraction unit, a calculation unit and a circulation unit.
The extraction unit is used for acquiring point cloud data and randomly extracting a predetermined number of point cloud data as first point cloud data by utilizing a random number generation function.
The calculating unit is used for calculating the mean value d_avg of the nearest neighbor distance of the first point cloud data by using a distance sorting method, taking the mean value d_avg as an initial buffer radius r, and calculating a buffer polygon of each point of the point cloud data D by using a buffer function; merging the buffer polygons to obtain a merged polygon B.
Wherein the nearest neighbor distance is the planar geometric distance from the target point to its nearest point. The buffer area is a space point set with the target point smaller than or equal to the specified radius; thus, the buffer of points is a circle; in the field of information systems, the boundary line of a circle is expressed as a series of ordered sets of vertices. The fused polygon B of the buffer area is a polygon obtained by merging the buffer areas of all the point cloud data.
The circulating unit is used for judging whether the fusion polygon B covers all the point cloud data and is a single polygon, if not, increasing the initial buffer radius r by a preset distance delta d, and recalculating the buffer polygon of each point of the point cloud data; merging the buffer area polygons to obtain a merged polygon B; and performing recursive calculation until the fusion polygon B covers all point cloud data and is a single polygon, and obtaining a final buffer fusion polygon B and a final buffer radius r (namely r=r+m delta d, m is the increasing number).
Wherein a single polygon is a single complete, non-segmented polygon. A single polygon may contain multiple inner rings.
The extraction module is used for extracting building polygon vertexes based on the buffer zone fusion polygon and the buffer zone radius to obtain a vertex set. Wherein, the extraction module includes: an outer ring extraction unit, a vertex extraction unit and a judgment unit.
The outer ring extraction unit is used for extracting the outer ring of the final buffer zone fusion polygon B, generating an outer ring polygon R', and calculating an inward contraction buffer zone polygon R with the radius of the final buffer zone increased by a preset distance (i.e. r+Deltad) as the radius.
Wherein the outer ring is a boundary between the polygonal inner space and the outer space, i.e., an outermost boundary. The inwardly contracting buffers are polygonal buffers having a negative radius, representing an inner area having a distance from the polygonal boundary line less than or equal to the buffer radius.
The vertex extraction unit is used for extracting all points outside the inward contraction buffer polygon R in the point cloud data D, and forming the external points into a building outer ring polygon vertex set P.
The judging unit is used for judging whether the inward contraction buffer zone polygon R is a simple polygon or not, if so, the building outer ring polygon vertex set P is a building boundary polygon vertex set; if not, sequentially extracting the inner ring C of the inward contraction buffer polygon R, searching the points contained in the inner ring buffer with the preset distance delta d as the radius, and forming an inner ring polygon vertex set.
The vertex sets extracted by all inner ring buffers of inward contraction buffer polygon R form all inner ring polygon vertex sets of the building, expressed as: e=e 1∪E2∪...∪En, where E i is the i-th set of polygon vertices of the building inner ring and n is the number of inner rings.
Wherein the simple polygon is a single polygon without an inner ring.
The generating module is used for sequentially generating an outer ring polygon and an inner ring polygon based on the vertex set, and obtaining a building boundary polygon based on the outer ring polygon and the inner ring polygon. Wherein, the generation module includes: an external polygon generating unit, an internal polygon generating unit, and a building polygon generating unit.
The external polygon generation unit is used for searching the vertex q of the inward contraction buffer polygon R closest to the point P in the polygon vertex set P of the outer ring of the building, and assigning the point P based on the sequence number of the vertex q (namely, assigning the sequence number of q to P); and sequentially connecting points of P after assignment according to assignment sequence numbers from small to large to form a closed multi-sense line, and converting the closed multi-sense line to generate a polygon M outside the building.
All vertexes of the polygon have a serial number, and the connection method is to sequentially connect the vertexes along the edge line in a anticlockwise manner from one vertex.
When the internal polygon generating unit judges that the internal ring polygon vertex set E is an empty set, the external polygon M of the building is a boundary polygon of the building; when the inner ring polygon vertex set E is not an empty set, processing each subset vertex of the inner ring polygon vertex set E according to the method of an external polygon generating unit to generate a polygon inside the building, wherein the polygon is expressed as: n= { N 1,N2,...,Nn }, where N i is the ith inner ring polygon of the building and N is the number of inner rings.
The building polygon generation unit is configured to remove (perform subtraction operation) the building interior polygon from the building exterior polygon, and obtain a building boundary polygon.
The above embodiments are merely illustrative of the preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but various modifications and improvements made by those skilled in the art to which the present invention pertains are made without departing from the spirit of the present invention, and all modifications and improvements fall within the scope of the present invention as defined in the appended claims.
Claims (7)
1. The building boundary polygon construction method based on the laser point cloud data is characterized by comprising the following steps of:
s1, acquiring point cloud data, and calculating a buffer area radius and a buffer area fusion polygon based on the point cloud data;
s2, extracting building polygon vertexes based on the buffer zone fusion polygon and the buffer zone radius to obtain a vertex set;
s3, sequentially generating an outer ring polygon and an inner ring polygon based on the vertex set, and obtaining a building boundary polygon based on the outer ring polygon and the inner ring polygon;
S1 comprises the following steps:
S11, acquiring the point cloud data, and extracting a preset number of the point cloud data to serve as first point cloud data;
S12, calculating the average value of the nearest neighbor distance of the first point cloud data, and calculating a buffer polygon of each point of the point cloud data by taking the average value as an initial buffer radius; merging the buffer area polygons to obtain a merged polygon;
S13, judging whether the fusion polygon covers all the point cloud data and is a single polygon, if not, increasing the radius of the initial buffer area by a preset distance, and recalculating the buffer area polygon of each point of the point cloud data; merging the buffer area polygons to obtain a merged polygon; and performing recursive calculation until the fusion polygon covers all the point cloud data and is a single polygon, and obtaining the final buffer fusion polygon and the final buffer radius.
2. The building boundary polygon construction method based on laser point cloud data as claimed in claim 1, wherein S2 comprises:
S21, extracting an outer ring of the final buffer zone fusion polygon, generating an outer ring polygon, and calculating an inward contraction buffer zone polygon with a radius which is increased by a preset distance by the final buffer zone radius;
s22, extracting all points outside the inward contraction buffer zone polygon in the point cloud data, and forming an outer ring polygon vertex set of the building from the external points;
S23, judging whether the inward contraction buffer area polygon is a simple polygon, if so, the building outer ring polygon vertex set is a building boundary polygon vertex set; if not, sequentially extracting inner rings of the inward contraction buffer zone polygons, searching points contained in the inner ring buffer zone with the preset distance as a radius, and forming an inner ring polygon vertex set.
3. The building boundary polygon construction method based on laser point cloud data as claimed in claim 2, wherein S3 comprises:
S31, searching the vertex of the polygon in the inward contraction buffer area closest to each point of the polygon vertex set of the outer ring of the building, and assigning a value to the polygon vertex of the outer ring of the building based on the serial number of the vertex; sequentially connecting the assigned vertices of the outer ring polygon of the building according to assignment sequence numbers from small to large to generate an outer polygon of the building;
s32, when the inner ring polygon vertex set is an empty set, the building outer polygon is the building boundary polygon; when the inner ring polygon vertex set is not an empty set, performing the calculation method of the step S31 on the points in the inner ring polygon vertex set to generate a polygon in the building;
S33, removing the building inner polygon from the building outer polygon to obtain the building boundary polygon.
4. A building boundary polygon construction system based on laser point cloud data for implementing the method of any of claims 1-3, comprising: the device comprises an acquisition module, an extraction module and a generation module;
the acquisition module is used for acquiring point cloud data and calculating a buffer area radius and a buffer area fusion polygon based on the point cloud data;
the extraction module is used for extracting building polygon vertexes based on the buffer zone fusion polygons and the buffer zone radius to obtain vertex sets;
The generating module is used for sequentially generating an outer ring polygon and an inner ring polygon based on the vertex set, and obtaining a building boundary polygon based on the outer ring polygon and the inner ring polygon.
5. The building boundary polygon construction system based on laser point cloud data as claimed in claim 4, wherein said acquisition module comprises: the device comprises an extraction unit, a calculation unit and a circulation unit;
the extraction unit is used for acquiring the point cloud data and extracting a preset number of the point cloud data to serve as first point cloud data;
the computing unit is used for computing a mean value of nearest neighbor distances of the first point cloud data, and computing a buffer polygon of each point of the point cloud data by taking the mean value as an initial buffer radius; merging the buffer area polygons to obtain a merged polygon;
The circulating unit is used for judging whether the fusion polygon covers all the point cloud data and is a single polygon, if not, increasing the radius of the initial buffer area by a preset distance, and recalculating the buffer area polygon of each point of the point cloud data; merging the buffer area polygons to obtain a merged polygon; and performing recursive calculation until the fusion polygon covers all the point cloud data and is a single polygon, and obtaining the final buffer fusion polygon and the final buffer radius.
6. The building boundary polygon construction system based on laser point cloud data of claim 5, wherein said extraction module comprises: an outer ring extraction unit, a vertex extraction unit and a judgment unit;
The outer ring extraction unit is used for extracting the outer ring of the final buffer zone fusion polygon, generating an outer ring polygon, and calculating an inward contraction buffer zone polygon with the radius of the final buffer zone increased by a preset distance as the radius;
The vertex extraction unit is used for extracting all points outside the inward contraction buffer zone polygon in the point cloud data, and forming an outer ring polygon vertex set of the building from the external points;
The judging unit is used for judging whether the inward contraction buffer polygon is a simple polygon or not, and if so, the polygon vertex set of the outer ring of the building is a polygon vertex set of the boundary of the building; if not, sequentially extracting inner rings of the inward contraction buffer zone polygons, searching points contained in the inner ring buffer zone with the preset distance as a radius, and forming an inner ring polygon vertex set.
7. The building boundary polygon construction system based on laser point cloud data of claim 6, wherein said generating module comprises: an external polygon generating unit, an internal polygon generating unit, and a building polygon generating unit;
The external polygon generation unit is used for searching the vertex of the inward contraction buffer polygon closest to each point of the polygon vertex set of the outer ring of the building, and assigning a value to the polygon vertex of the outer ring of the building based on the serial number of the vertex; sequentially connecting the assigned vertices of the outer ring polygon of the building according to assignment sequence numbers from small to large to generate an outer polygon of the building;
When the internal polygon generating unit judges that the inner ring polygon vertex set is an empty set, the building external polygon is the building boundary polygon; when the inner ring polygon vertex set is not an empty set, generating an inner polygon of the building according to the working process of the outer polygon generating unit by each point of the inner ring polygon vertex set;
The building polygon generation unit is used for removing the building interior polygon from the building exterior polygon to obtain the building boundary polygon.
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