Expressway bridge extraction method based on DEM data

Abstract

The invention discloses an expressway bridge extraction method based on DEM data, and the method comprises the steps: S1, building a buffer region through employing a region which is extended outwards by a certain distance from the center line of an expressway road, and carrying out the logic AND processing of the buffer region and a registered DEM, and obtaining a DEM region of an expressway; s2, performing gradient analysis on the DEM area of the expressway, and judging whether the DEM area is a bridge area or not through a gradient threshold in combination with the characteristic that the long side of the bridge is higher than the ground; and S3, combining the characteristics that the short edges of the bridge are connected with the ground, extracting the short edges of the bridge by adopting a smoothness threshold value, carrying out intersection calculation on the short edges of the bridge and the center line, and extracting the bridge. According to the method, the advantages of DEM data and bridge characteristics are combined, so that rapid extraction of the bridge on the expressway can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of bridge monitoring, and in particular to a method for extracting highway bridges based on DEM data. Background Art

[0002] Bridges are one of the important man-made structures. The detection and recognition of bridge targets are of great significance for global positioning system data acquisition, map updating and auxiliary supervision of bridge construction. Due to the complex environment around roads and bridges, the shadows of bridges themselves generated by buildings, vegetation, road greening and light illumination bring certain difficulties to bridge extraction. At present, the research work on bridge recognition algorithms and bridge extraction algorithms is largely focused on image-based extraction, and most of them are mostly carried out for water bridge targets. The basic idea is to first extract the river water body, and then detect the bridge based on the position relationship between the river and the bridge. However, the existing bridge detection methods rely on river extraction, and it is difficult to achieve land bridge detection. Because the background under the land bridge is no longer a river, but land, its scattering characteristics and shape distribution are different from those of the river. The traditional water body extraction method cannot be used to detect the land background, and thus the bridge cannot be located using the prior knowledge of the bridge's position. Summary of the invention

[0003] In view of the above problems, the present invention proposes a method for extracting highway bridges based on DEM data. DEM data can provide elevation information of the terrain and three-dimensional information of the surface, and can accurately reflect the undulation and slope of the surface. At the same time, since the bridge points are higher than the surrounding ground points and the foot points at both ends of the bridge deck are smoothly connected to the ground points, the combination can be effectively used to identify and extract the outline of the highway bridge.

[0004] A highway bridge extraction method based on DEM data comprises the following steps: S1, using the area extending a certain distance outward from the center line of the highway to establish a buffer zone, and performing logical AND processing with the registered DEM to obtain the DEM area of ​​the highway; S2, conduct slope analysis on the DEM area of ​​the highway, and combine the characteristics of bridge length, side, and height above the ground to determine whether it is a bridge area through the slope threshold; S3, combining the feature that the short side of the bridge is connected to the ground, uses the smoothness threshold to extract the short side of the bridge, and performs an intersection operation between the short side of the bridge and the center line to extract the bridge.

[0005] Preferably, the step S1 comprises: S1-1, based on the center line of the expressway, a buffer zone Road_Buffer1 of the center line of the road is generated with a buffer distance of 1.5 times the road width; S1-2, generate a buffer zone Road_Buffer2 of the road centerline with the road width as the buffer distance; S1-3. Clip the buffer Road_Buffer1 with the high-resolution DEM data to generate the DEM area Road_Dem1 of the expressway.

[0006] Preferably, the step S2 comprises: S2-1, performing slope analysis on the DEM area Road_Dem of the expressway to generate the slope of the DEM area Road_Dem1 of the expressway; S2-2, setting a slope threshold, judging whether it is a bridge according to the slope threshold, and extracting the area D_area exceeding the slope threshold; S2-3. Perform an intersection operation on D_area and Road_Buffer2 to extract the bridge area D_Bridge of the highway.

[0007] Preferably, step S3 comprises: S3-1. Determine whether it is the short side of the bridge by calculating the smoothness in the bridge area D_Bridge. Fit the plane with the 20 neighborhood points of each point in the DEM. The residual standard deviation between the actual value and the fitted value is the smoothness of the point. S3-2, setting a smoothness threshold, the points below the threshold are the points on the short side of the bridge, and the short side vector line of the bridge is generated by least squares fitting; S3-3. Find the intersection point of the short side vector line of the extracted bridge and the center line of the highway, and cut the center line of the highway at the intersection point, so as to extract the bridge on the highway. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is an overall flow chart of the highway bridge extraction method based on DEM data provided by the present invention. DETAILED DESCRIPTION

[0009] The following is a further detailed description of a highway bridge extraction method based on DEM data of the present invention in conjunction with the accompanying drawings and specific embodiments: Example

[0010] like Figure 1 As shown, the present invention proposes a highway bridge extraction method based on DEM data, including: S1, use the area extending a certain distance outward from the center line of the highway to establish a buffer zone, and perform logical "AND" processing with the aligned DEM to obtain the DEM area of ​​the highway.

[0011] S2, perform slope analysis on the DEM area of ​​the highway, and combine the feature that the long side of the bridge is higher than the ground to determine whether it is a bridge area through the slope threshold.

[0012] S3, combining the feature that the short side of the bridge is connected to the ground, uses the smoothness threshold to extract the short side of the bridge, and performs an intersection operation between the short side of the bridge and the center line to extract the bridge.

[0013] Preferably, the step S1 comprises: S1-1. In order to avoid the influence of mountains and water systems outside the expressway and reduce redundant calculations, a buffer zone Road_Buffer1 of the road centerline is generated based on the centerline of the expressway and 1.5 times the road width as the buffer distance.

[0014] S1-2. Generate a buffer zone Road_Buffer2 for the road centerline using the road width as the buffer distance.

[0015] S1-3. Clip the buffer Road_Buffer1 with the high-resolution DEM data to generate the DEM area Road_Dem1 of the expressway.

[0016] Preferably, the step S2 comprises: S2-1. Since the long side height of the highway bridge is higher than the surrounding ground elevation, the area around the bridge is very steep and has a high slope value. Slope analysis is performed on the highway DEM area Road_Dem to generate the slope of the highway DEM area Road_Dem1.

[0017] S2-2, setting a slope threshold, judging whether it is a bridge according to the slope threshold, and extracting an area D_area exceeding the slope threshold.

[0018] S2-3. Since the slopes on both sides of the expressway are also high, the extracted area D_area may contain the slopes through the threshold judgment. Therefore, D_area is intersected with Road_Buffer2 to extract the bridge area D_Bridge of the expressway.

[0019] Preferably, step S3 comprises: S3-1. After extracting the bridge area, since the short side of the bridge must be connected to the ground, the smoothness of the bridge area D_Bridge is calculated to determine whether it is the short side of the bridge. The plane is fitted with 20 neighborhood points of each point in the DEM, and the residual standard deviation of the actual value and the fitted value is the smoothness of the point.

[0020] S3-2. Set a smoothness threshold. Points below the threshold are points on the short side of the bridge. Generate the short side vector line of the bridge through least squares fitting.

[0021] S3-3. The intersection point of the short side vector line of the extracted bridge and the center line of the highway is found, and the center line of the highway is cut off at the intersection point, so that the bridge on the highway can be extracted.

[0022] The examples of the present invention are described in detail above in conjunction with the embodiments, but the present invention is not limited to the above examples. Various changes can be made within the knowledge scope of ordinary technicians in the field without departing from the purpose of the present invention, and should also be regarded as the protection scope of the present invention.

Claims

1. A highway bridge extraction method based on DEM data, characterized in that: The following steps are involved: S1, using the area extending a certain distance outward from the center line of the highway to establish a buffer zone, and performing logical AND processing with the registered DEM to obtain the DEM area of ​​the highway; S2, conduct slope analysis on the DEM area of ​​the highway, and combine the characteristics of bridge length, side, and height above the ground to determine whether it is a bridge area through the slope threshold; S3, combining the feature that the short side of the bridge is connected to the ground, uses the smoothness threshold to extract the short side of the bridge, and performs an intersection operation between the short side of the bridge and the center line to extract the bridge.

2. The highway bridge extraction method based on DEM data according to claim 1 is characterized in that: The step S1 comprises: S1-1, based on the center line of the expressway, a buffer zone Road_Buffer1 of the center line of the road is generated with a buffer distance of 1.5 times the road width; S1-2, generate a buffer zone Road_Buffer2 of the road centerline with the road width as the buffer distance; S1-3. Clip the buffer Road_Buffer1 with the high-resolution DEM data to generate the DEM area Road_Dem1 of the expressway.

3. The highway bridge extraction method based on DEM data according to claim 1 is characterized in that: The step S2 comprises: S2-1, performing slope analysis on the DEM area Road_Dem of the expressway to generate the slope of the DEM area Road_Dem1 of the expressway; S2-2, setting a slope threshold, judging whether it is a bridge according to the slope threshold, and extracting the area D_area exceeding the slope threshold; S2-3. Perform an intersection operation on D_area and Road_Buffer2 to extract the bridge area D_Bridge of the highway.

4. The highway bridge extraction method based on DEM data according to claim 1 is characterized in that: The step S3 comprises: S3-1. Determine whether it is the short side of the bridge by calculating the smoothness in the bridge area D_Bridge. Fit the plane with the 20 neighborhood points of each point in the DEM. The residual standard deviation between the actual value and the fitted value is the smoothness of the point. S3-2, setting a smoothness threshold, the points below the threshold are the points on the short side of the bridge, and the short side vector line of the bridge is generated by least squares fitting; S3-3. Find the intersection point of the short side vector line of the extracted bridge and the center line of the highway, and cut the center line of the highway at the intersection point, so as to extract the bridge on the highway.

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