CN113012286A

CN113012286A - Method for constructing road DEM (digital elevation model) based on dense point cloud data

Info

Publication number: CN113012286A
Application number: CN202110306452.2A
Authority: CN
Inventors: 赵明伟; 江岭; 王靖; 杨灿灿; 徐燕; 张婉玉
Original assignee: Chuzhou University
Current assignee: Chuzhou University
Priority date: 2021-03-23
Filing date: 2021-03-23
Publication date: 2021-06-22
Anticipated expiration: 2041-03-23
Also published as: CN113012286B

Abstract

The invention discloses a method for constructing a road DEM (digital elevation model) based on dense point cloud data. The method comprises the following steps: s1, performing sub-unit division on the road; s2, calculating an elevation average value in each road subunit based on the dense point cloud data; s3, modifying the average elevation value of each road subunit according to the set maximum fluctuation threshold value of the road; s4, generating a DEM grid of a modeling area, and overlapping the DEM grid with the road subunits; s5, calculating the elevation value of the DEM center grid point based on the spatial position relationship between the grid center point and the road subunit and the elevation value of the road subunit; and S6, sequentially finishing the calculation of the elevation values of the central points of all DEM grids, and outputting the calculation results according to the grid data specification. The method comprises two key technical links of determining the elevation value of the road subunit and calculating the elevation value of the central point of the DEM grid, and can effectively ensure the elevation precision and morphological characteristics of road DEM modeling.

Description

Method for constructing road DEM (digital elevation model) based on dense point cloud data

Technical Field

The invention belongs to the technical field of high-precision digital elevation model construction, and relates to a method for realizing construction of a road DEM (digital elevation model) by considering morphological characteristics and dense point cloud data characteristics of a road so as to ensure that the constructed road DEM has higher morphological precision and elevation precision.

Background

A Digital Elevation Model (DEM) is a solid ground Model which realizes Digital simulation of ground terrain through limited terrain Elevation data and expresses the ground Elevation in a group of ordered numerical array forms. DEM is the core content of the national basic geographic database, and has wide application in the fields of traffic, military, water conservancy, agriculture, environment, resource management, planning, tourism and the like.

The current main DEM construction method is suitable for continuously changing natural terrains, however, in areas with obvious human activity traces such as cities, various human engineering creates a plurality of discontinuous terrains such as roads, dams, slopes and the like, wherein the roads are used as framework parts of the terrains of the urban areas, and the high-precision terrain modeling is regarded by the related fields. Unlike natural undulating terrain, roads have significant morphological features, such as generally clear road boundaries and regular shapes from a morphological standpoint, and generally undulate longitudinally over a range of gradients from an elevation change perspective and substantially negligible elevation change laterally. Therefore, when the road DEM is constructed, the characteristics of geometric information and semantic information such as roads need to be considered, and the constructed road DEM can be ensured to conform to the morphological characteristics of the actual road.

In the field of road DEM construction, morphological characteristics of roads are less considered in the past, and the road DEM is obtained by performing spatial interpolation by adopting interpolation methods such as kriging, splines and the like on the basis of topographic data such as elevation points, characteristic lines and the like. Later, learners realized that the road morphology is obviously different from other areas, and tried to use the road boundary as constraint information to distinguish the road from the adjacent areas, but the improvement of the construction result is not obvious because the special morphology of the road is not considered when the DEM is constructed in the road. Recent researchers have proposed a road DEM modeling method based on morphological and semantic features, which takes large-scale topographic map data as a data source, takes morphological features of a road modeling result as a main target, screens elevation point data, and then realizes the construction of the road DEM by relying on a spatial interpolation technology. The road DEM constructed by the method is in accordance with the actual road form in form, but the adopted data is too sparse, so that the elevation precision of the constructed road DEM is difficult to guarantee, and in addition, the large-scale topographic map is high in acquisition cost, and the method is difficult to popularize and apply.

Disclosure of Invention

In order to solve the problems of the prior art, morphological characteristics of the road surface can be combined with dense characteristics of available modeling data, on one hand, the elevation value of the road DEM is calculated mainly by observation data and assisted by a spatial interpolation technology; on the other hand, the road DEM also needs to be smoothed appropriately to ensure the correct shape of the road. Therefore, the invention provides a method for constructing a road DEM based on dense point cloud data, which can well express the road form while keeping the elevation precision.

The technical scheme adopted by the invention is as follows:

a method for constructing a road DEM based on dense point cloud data comprises the following steps: firstly, performing subunit division on a road, and calculating the average elevation value of each road subunit based on dense point cloud data; then, modifying the average elevation value of each road subunit according to the set maximum fluctuation threshold value of the road; then, generating a DEM grid of a modeling area, and overlapping the DEM grid with the road subunits; and finally, traversing the DEM grid, and calculating the elevation value of the DEM grid based on the spatial position relationship between the grid center point and the road subunit and the elevation value of the road subunit.

Further, the method specifically comprises the following steps:

s1, dividing the road sub-unit, namely dividing the planar road data into a series of cells according to a certain step length, wherein if the road is intersected, the intersection is taken as a sub-unit; after the sub-units are divided, generating a road sub-unit central point;

s2, calculating an elevation average value in each road subunit based on the dense point cloud data, and assigning the value to a road subunit central point;

s3, calculating and adjusting the elevation average value of each subunit of the road by adopting a Douglas algorithm, so that the elevation change rate between adjacent road subunits is not higher than a preset threshold value;

s4, generating a central grid point of a modeling area grid DEM grid, and carrying out spatial superposition with road subunit data;

s5, calculating the elevation value of the DEM center grid point according to the position relation between the center grid point of the DEM grid and the center points of the road subunits on the two sides of the DEM grid and the principle of linear elevation change between the two road subunits;

and S6, sequentially finishing the calculation of the elevation values of the central points of all DEM grids, and outputting the calculation results according to the grid data specification.

Further, the specific process of step S3 is as follows:

s31, marking the elevation values of the road subunits at the road head A and the road tail B in the road to be processed as uneditable, namely determining the elevation values at the positions;

s32, taking the current processed road as a main road, judging whether the road is intersected with other roads, if so, marking the elevation value of a road subunit formed at the intersection of the intersected roads as uneditable, namely, the elevation value at the intersection is determined;

s33, projecting the center point of the road subunit to a two-dimensional space from a three-dimensional space, wherein the X coordinate of the road head A is 0, and the Y coordinate is the elevation value of the road head A; the X coordinates of the center points of the other cells are the distances from the road head A, the distance values are calculated along the extending direction of the road, and the Y coordinates are the elevation values of the distance values;

s34, projection points corresponding to the geometric center points of the two sub-units of the road head A and the road tail B are marked as A1 and B1 respectively, and the expression of a straight line A1B1 is determined according to the three-dimensional coordinates of the projection points;

s35, traversing unmarked projection points between the projection points A1 and B1, and determining a point C1 to ensure that the distance from the point C1 to the straight line A1B1 is farthest;

s36, calculating elevation change rates of straight lines A1C1 and C1B1, comparing the elevation change rates with a set threshold value, modifying the elevation value of a point C1 if the elevation change rate is larger than the set threshold value so that the calculated elevation change rate is equal to the set threshold value, dividing the original road into two new sections of roads, namely straight lines A1C1 and B1C1, respectively taking points A1 and C1, B1 and C1 as two end points of the new road, and repeating the steps S34-S35; if the elevation change rate is smaller than the set threshold, the elevation value at the point C1 is not changed, the point C1 is marked as processed, and then the step S35 is executed;

and S37, after all the projection points are marked, assigning the elevation values of the projection points to the central points of the original road subunits, and completing the updating of the elevation values of the central points of the road subunits.

Further, the specific process of step S5 is as follows:

s51, passing through the center point of each road subunit to generate a perpendicular line of the road center line;

s52, sequentially traversing the DEM grid central points superposed with the currently processed road, and determining the vertical lines of the central lines at the two sides of the DEM grid central points, wherein the vertical lines are marked as L1 and L2 respectively;

s53, calculating the distances between the DEM grid center point of the elevation value to be calculated and the vertical lines L1 and L2, and marking the distances as d1 and d2 respectively;

s54, calculating the elevation value of the center point of the current DEM grid according to the linear change principle based on the elevation values V1 and V2 of the center points of the subunits corresponding to d1, d2, L1 and L2, wherein the calculation formula is as follows:

and S55, repeating the steps S52-S54 until the calculation of the elevation values of the center points of all DEM grids intersected with the current road is completed.

The method is based on dense point cloud data, comprises two key technical links of determining the elevation value of a road subunit and calculating the elevation value of the central point of the DEM grid, and can effectively ensure the elevation precision and morphological characteristics of the road DEM modeling. The invention has the technical characteristics and beneficial effects that:

(1) the road DEM construction method provided by the invention fully considers the morphological characteristics of roads, abandons the traditional DEM interpolation method, designs the calculation method of the DEM grid elevation value according to the elevation variation characteristics of road surfaces in different directions, and can well ensure the morphological characteristics of DEM construction results.

(2) The road DEM construction method provided by the invention takes the dense point cloud data as an elevation information source, can ensure the elevation precision of the DEM result to the maximum extent, and accords with the development trend of the current data acquisition and modeling land.

Drawings

FIG. 1 is a flow chart of the method of the present invention;

FIG. 2 is a schematic diagram of a road sub-unit partition;

FIG. 3 is a schematic diagram of dense elevation points in a road sub-unit;

FIG. 4 is a schematic diagram of a center point of a road sub-unit;

FIG. 5 is a schematic diagram of a road subunit center point projected under a two-dimensional coordinate system;

FIG. 6 is a schematic diagram illustrating adjustment of elevation values of center points of road subunits;

FIG. 7 is a schematic diagram of the superposition of a road subunit and a DEM grid unit to be constructed;

FIG. 8 is a schematic illustration of a perpendicular to a center line of a roadway generated within a roadway subunit;

FIG. 9 is a schematic diagram of a spatial position relationship between a DEM grid central point and a road sub-unit;

FIG. 10 is a schematic diagram of elevation calculation of a central point of a DEM grid;

FIG. 11 is a road map in the example;

FIG. 12 is a diagram of road sub-units generated by a road in an embodiment;

FIG. 13 is a road DEM constructed by the method of the present invention in an embodiment;

FIG. 14 is a road DEM constructed by the inverse distance weighting method in the embodiment;

FIG. 15 is a graph of slope versus results of the method of the present invention in an example embodiment;

fig. 16 is a gradient map corresponding to the result of the inverse distance weighting method in the embodiment.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.

The method comprises the steps of dividing a road into road subunits, calculating the average elevation value of each subunit based on dense point cloud data, and determining the elevation values of a road head, a road tail and a road junction; modifying the average elevation value of each road subunit according to the set maximum fluctuation threshold value of the road; then, generating a DEM grid of a modeling area, and overlapping the DEM grid with the road subunits; and finally, traversing the DEM grid, and calculating the elevation value of the DEM grid based on the spatial position relationship between the grid center point and the road subunit and the elevation value of the road subunit.

As shown in fig. 1, the method for constructing a road DEM based on dense point cloud data in the embodiment specifically includes the following steps:

step 1: and dividing the road subunits. Dividing the road surface data into a series of cells according to a certain step length, wherein if the road is intersected, the intersected road is taken as a subunit (figure 2).

Step 2: based on the dense point cloud data, an average elevation value for each road sub-unit is calculated from the elevations of the points within the cells (FIG. 3), and then the calculated average value is assigned to the geometric center point of each road sub-unit (FIG. 4).

And step 3: and determining the elevation values of the road head and the road tail. And marking the elevation values of the road subunits at the head and the tail of the road in the currently processed road as uneditable, namely determining the elevation values at the position.

And 4, step 4: and determining the elevation value at the road junction. And taking the currently processed road as a main road, judging whether the road is intersected with other roads, if so, marking the elevation value of a road subunit formed at the intersection of the intersected roads as uneditable, namely, the elevation value at the intersection is determined.

And 5: and projecting the road unit center point into a two-dimensional space from the three-dimensional space, wherein the road head (A) is projected into the two-dimensional space to be A1, the X coordinate of the road head is 0, the Y coordinate of the road head is the elevation value of A, the other road unit center points are projected into a two-dimensional plane, the X coordinate of the road unit center points is the distance from the center point to the road head center point A, and the Y coordinate of the road unit center points is the elevation value of the other road unit center points (figure 5).

Step 6: and connecting the head (A1) point and the tail (B1) point after projection, namely the road head and the road tail corresponding to the original road, and determining the expression of a straight line A1B1 by two points A1 and B1.

And 7: traversing the projection points corresponding to the central points of the unmarked road sub-units between A1 and B1, calculating the distance from each projection point to the straight line A1B1, selecting the projection point C1 (figure 6) corresponding to the central point of the sub-unit with the farthest distance, and calculating the maximum distance to be H_ABMAX(ii) a The maximum distance calculation formula is as follows:

in the formula: a is the y coordinate variation of the straight line A1B1, i.e., a is y_B-y_AB is the x coordinate variation of the straight line A1B1, i.e., B is x_B-x_AAnd c is expressed as: c ═ y_B-y_A)*x_B-(x_B-X_A)*y_B。

And 8: calculating the elevation change rate K of the straight lines A1C1 and C1B1_acAnd K_bcComparing the elevation change rate with a set threshold value, modifying the elevation value of C1 if the elevation change rate is greater than the threshold value, so that the calculated elevation change rate is equal to the set threshold value, dividing the original road into two new roads, namely straight lines A1C1 and B1C1, respectively taking points A1 and C1, B1 and C1 as two end points of the new road, and repeating the step 6-8; if the elevation change rate is less than the threshold, the elevation value at C1 is not changed, and point C1 is marked as processed, and step 7 is executed again.

And step 9: and after all the projection points are marked, assigning the elevation values of the projection points to the central points of the corresponding subunits of the original road, and finishing the updating of the elevation values of the central points of the subunits of the road.

Step 10: a grid DEM central grid point is generated in the study area, the grid size is smaller than the road sub-unit, and is superimposed with the road sub-unit data (fig. 7).

Step 11: based on the road centerline, a perpendicular to the road centerline is generated through the center point of each road sub-unit (FIG. 8).

Step 12: and sequentially traversing DEM grid central points overlapped with the currently processed road, and if the DEM grid is completely positioned in one road subunit, assigning the geometric central point elevation value of the subunit to the grid central point (figure 9).

Step 13: if the DEM grid spans two road sub-units, the vertical lines of the road center lines on both sides of the center point of the sub-unit (V1 and V2) are determined and marked as L1 and L2, respectively. Generating L1 and L2 vertical lines by passing through the central point of the DEM grid with the elevation value to be calculated, and calculating the distances between the central point of the grid and L1 and L2, and marking as d1 and d2 (figure 10).

Step 14: based on the elevation values of d1 and d2, V1 and V2, calculating the elevation value of the central point of the current DEM grid according to the linear change principle, wherein the calculation formula is as follows:

step 16: and (5) repeatedly executing the steps 12 to 14 until the calculation of the elevation values of the central points of all DEM grids intersected with the current road is completed, and outputting the calculation result according to the grid data specification.

Examples

In order to verify the effect of the method for constructing the DEM, the embodiment selects a part of roads (shown in figure 11) inside Chuzhou academy in Chuzhou city of Anhui province for constructing the DEM, and the adopted dense elevation point data is acquired by carrying an elevation information acquisition instrument by an unmanned aerial vehicle. The DEM construction implementation steps applying the method of the invention are as follows:

step 1: the planar road data is divided into a series of cells according to a step length of 5m, wherein if a road is intersected, the intersection is taken as a subunit. (FIG. 12)

Step 2: and calculating an elevation average value in each road subunit based on the dense point cloud data.

And step 3: when the average elevation value of each subunit of the road is calculated and adjusted, the threshold value of the elevation change rate is set to be 0.05, and the elevation value of the elevation point exceeding the threshold value is modified, so that the calculated elevation change rate is equal to the set threshold value.

And 4, step 4: and generating a grid DEM central grid point, and superposing the grid point with the road subunit data.

And 5: and calculating the elevation value of each DEM central grid point according to the position of the DEM central grid point and the elevation value of the road subunit.

Step 6: and (3) constructing a DEM (figure 13) with the pixel size of 1 meter, and performing road DEM interpolation by adopting a traditional spatial interpolation method (taking an inverse distance weighted interpolation method as an example) for comparison, wherein the result is shown in figure 14. It can be seen that the road DEM constructed by the two methods is basically consistent in elevation change, and the elevation change of the method is slightly smaller than that of the traditional method.

Based on the result of the invention and the result of the inverse distance weighting method, a slope map (fig. 15 and fig. 16) is generated, and it can be seen that the slope obtained by the method of the invention basically changes in the road extending direction and accords with the road form characteristics, while the slope change of the traditional method is obviously more complex and does not accord with the road form characteristics.

By combining the analysis, the road DEM constructed by the method disclosed by the invention well keeps the morphological characteristics of the road, and is suitable for constructing the high-precision DEM in the regions such as cities.

Claims

1. A method for constructing a road DEM based on dense point cloud data is characterized by comprising the following steps: firstly, performing subunit division on a road, and calculating the average elevation value of each road subunit based on dense point cloud data; then, modifying the average elevation value of each road subunit according to the set maximum fluctuation threshold value of the road; then, generating a DEM grid of a modeling area, and overlapping the DEM grid with the road subunits; and finally, traversing the DEM grid, and calculating the elevation value of the DEM grid based on the spatial position relationship between the grid center point and the road subunit and the elevation value of the road subunit.

2. The method for constructing the road DEM based on the dense point cloud data as claimed in claim 1, wherein the method comprises the following steps:

3. The method for constructing the road DEM based on the dense point cloud data as claimed in claim 2, wherein the specific process of the step S3 is as follows:

4. The method for constructing the road DEM based on the dense point cloud data as claimed in claim 2, wherein the specific process of the step S5 is as follows: