JP7540710B2 - Anti-aircraft markings - Google Patents

Description

The present invention relates to an airborne marker used in surveying using a laser scanner mounted on an unmanned aerial vehicle (UAV).

Regarding public surveys using UAVs, the Geospatial Information Authority of Japan has drawn up a "Manual for Public Surveys Using UAVs (draft)." This manual is divided into the creation of digital topographical maps and three-dimensional point clouds, both of which use aerial photographs taken by UAVs.

When creating a digital topographical map or a three-dimensional point cloud using aerial photographs taken by a UAV, control points are set up. Setting control points refers to the task of setting up points (hereafter referred to as control points) that serve as reference points for horizontal position and elevation required for aerial triangulation.

Anti-aircraft signs are installed at control points. The shape, size, color, etc. of anti-aircraft signs are selected so that they can be seen on enlarged aerial photographs. Specific anti-aircraft sign patterns are described in the above-mentioned manual. The anti-aircraft sign shown in Figure 6 has ★, X, +, and O patterns painted on the top surface of a base with a square outer shape. The manual also specifies the size, stating that the "standard size is that the side length or circular diameter of the pattern is 15 pixels or more."

Previously, there have been proposals for airborne markers and UAV aerial photography surveying systems that can extract or specify reference points from within airborne markers in captured images, improving the accuracy of the generated survey data (see, for example, Patent Document 1).

In surveying using a UAV-mounted laser scanner, a laser beam is projected at a specific altitude at a specified rate onto an anti-aircraft beacon installed at a control point, and the intensity of the laser reflection from the beacon is measured. If the pattern area of the anti-aircraft beacon is black (dark color) and the area surrounding the pattern is white (light color), the intensity of the reflection from the pattern area will be relatively stronger than the intensity of the reflection from the area surrounding the pattern. The laser beam can also be used to measure the distance to the anti-aircraft beacon, and the height (altitude) of the anti-aircraft beacon can be calculated relative to the UAV altitude. In surveying using a UAV-mounted laser scanner, the measurement data measured in the laser scan area that includes the anti-aircraft beacon is called a "point cloud."

The system extracts point cloud data from anti-aircraft beacons, recognizes point cloud data with different reflectance rates from their reflection intensity, and identifies the center point of the anti-aircraft beacon corresponding to the control point from the pattern of a known shape.

JP 2019-60641 A

However, because anti-aircraft signs have a square outer shape in a plan view, if the point cloud on the anti-aircraft sign is missing, it is not easy to identify the center point of the anti-aircraft sign.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide an anti-aircraft marker that can easily identify the center point of the anti-aircraft marker even if the point cloud on the anti-aircraft marker is missing, thereby improving the accuracy of the survey data.

One aspect of the anti-aircraft marker of the present invention is an anti-aircraft marker used for surveying by a laser scanner mounted on an unmanned aerial vehicle, comprising a base made of a thin body and a pattern displayed on at least one surface in the thickness direction of the base, at least a portion of the outer shape of the base is formed in an arc shape , the reference pattern comprises a plurality of squares that are point-symmetric with respect to the center of the base, and each of the plurality of squares has one of its four corners located at the center of the base and one of its other corners located on or near the outer periphery of the base .
Another aspect of the anti-aircraft marker of the present invention is an anti-aircraft marker used for surveying by a laser scanner mounted on an unmanned aerial vehicle, comprising a base made of a thin body and a reference pattern represented on at least one surface in the thickness direction of the base, at least a portion of the outer shape of the base is formed in an arc shape, the reference pattern comprises a plurality of triangles that are point-symmetric with respect to the center of the base, and each of the plurality of triangles has one of three corners located at the center of the base and the other two corners located on the outer peripheral edge of the base or inwardly away from the outer peripheral edge.
Yet another aspect of the anti-aircraft marker of the present invention is an anti-aircraft marker used for surveying by a laser scanner mounted on an unmanned aerial vehicle, comprising a base made of a thin body and a reference pattern displayed on at least one surface in the thickness direction of the base, at least a portion of the outer shape of the base is formed in an arc-like shape, the reference pattern has a plurality of shapes that are point-symmetric with respect to the center of the base, and on the surface of the base on which the reference pattern is displayed, a non-forming area of the reference pattern is formed in a predetermined area that includes the center position of the anti-aircraft marker on the inside, and the outer shape of the non-forming area is at least partially formed in an arc-like shape.

According to the present invention, it is possible to provide an anti-aircraft marker that can easily identify the center point of the anti-aircraft marker even if the point cloud on the anti-aircraft marker is missing, thereby improving the accuracy of the survey data.

FIG. 2 is a plan view of an anti-aircraft marker according to an embodiment of the present invention. 1 is a schematic perspective view of an anti-aircraft marker according to an embodiment of the present invention; 3A and 3B are plan views of an anti-aircraft marker according to a modified example. FIG. 13 is a plan view of an anti-aircraft marker relating to another modified example. FIG. 13 is a plan view of an anti-aircraft marker relating to yet another modified example. FIG. 1 is a plan view of various conventional anti-aircraft markers. FIG. 7A is an example of a point cloud of an anti-aircraft marker according to an embodiment, and FIG. 7B is an explanatory diagram of center detection in the point cloud of FIG. 7A. FIG. 8A is an example of a point cloud of an anti-aircraft sign according to a comparative example, and FIG. 8B is an explanatory diagram of center detection in the point cloud of FIG. 8A. FIG. 9A is another example of a point cloud at an anti-aircraft marker in the embodiment, and FIG. 9B is another example of a point cloud at an anti-aircraft marker in the comparative example. 13 is yet another example of a point cloud of an anti-aircraft marker according to a comparative example. 11A and 11B are plan views of an anti-aircraft marker according to a modified example different from that described above.

Below, an embodiment of the present invention will be described in detail with reference to the attached drawings. Note that the present invention is not limited to the embodiment described below, and can be modified as appropriate without departing from the gist of the present invention. For the sake of convenience, some components may be omitted from the following figures. The orientation of each component in the following embodiment is merely an example, and can be changed to any orientation.

Figure 1 is a plan view of an anti-aircraft marker according to an embodiment. The anti-aircraft marker 10 is used for surveying by a laser scanner mounted on a UAV and is installed at a control point. In such surveying, the anti-aircraft marker 10 is irradiated with laser light from the UAV, and the center position of the anti-aircraft marker 10 can be analyzed from the laser point cloud using the laser points on the anti-aircraft marker 10.

The anti-aircraft marker 10 comprises a base 11 made of a thin body and a reference pattern 12 displayed on the top surface 11a, which is at least one surface of the base 11 in the thickness direction.

The external shape of the base 11 is circular (perfectly circular) when viewed from a direction parallel to its thickness direction. The base 11 is formed from a plate-like member made of wood, synthetic resin, or the like. A hole 11b is formed in the center of the base 11, and is used for attaching the leg members described below through the hole 11b. The rigidity of the base 11 is set to such an extent that the base 11 does not flex or flexes slightly when supported from below only around the area where the hole 11b is formed.

The reference pattern 12 can be any of the patterns shown in FIG. 6, and is not limited as long as position analysis can be performed by the above-mentioned surveying, but in this embodiment, the +-shaped reference pattern 12 in FIG. 6 is used. Such a +-shaped reference pattern 12 is represented by two squares 12a that are painted black or a dark color equivalent to black, forming a checkerboard pattern. The top surface 11a of the base 11 other than the two squares 12a is white or a light color similar to white (for example, the bare wood of wood).

Going into further detail about the reference pattern 12, the radial position of the base 11 and the diagonal position of the squares 12a are the same, and one square 12a is arranged symmetrically with respect to the other square 12a, with the center of the base 11 being the point of symmetry. Thus, one of the four corners of each square 12a is located at the center of the base 11, and one of the other corners is located on or near the outer edge of the base 11. The position where the corners of the two squares 12a are located and which is the center of the base 11 is regarded as the reference point of the anti-aircraft sign 10.

Figure 2 is a schematic perspective view of an anti-aircraft sign according to an embodiment. As shown in Figure 2, the anti-aircraft sign 10 may further include a leg member 15. The leg member 15 is inserted or fitted into a hole 11b in the base 11 and attached to the bottom surface 11c of the base 11. The leg member 15 has a structure similar to that of a tripod. Specifically, the leg member 15 has a vertical portion 15a extending downward from the bottom surface 11c of the base 11, and installation portions 15b provided at 120° intervals around the periphery of the vertical portion 15a and installed on a mounting surface (ground). The length of the installation portions 15b can be adjusted by a telescopic structure or the like, and the height position of the base 11 from the mounting surface can be changed by this adjustment.

According to this embodiment, even if half or more of the points on the anti-aircraft sign 10 are missing when laser light is irradiated from the UAV, if at least a portion of the arc that forms the outer periphery of the base 11 can be identified, the center (reference point) of the anti-aircraft sign 10 can be derived from its shape.

Here, we will compare the anti-aircraft sign 10 of this embodiment with the +-shaped anti-aircraft sign with a square planar shape in Figure 6 (hereinafter referred to as the "conventional anti-aircraft sign").

Compared to conventional anti-aircraft signs, the circular shape of the present embodiment is more effective in detecting the center position of the anti-aircraft sign 10, whether it is detected by analysis software or searched for by an operator. Also, by making it circular like the present embodiment, it is easier to determine the center position even if part of the anti-aircraft sign 10 is missing when recognized from the air.

When the positions of the outer edge of the reference pattern and the outer edge of the base are roughly aligned, as in conventional anti-aircraft markers, there is a problem that it is difficult to recognize the laser point or points with different reflectance in the area where the outer edge of the black part of the reference pattern and the outer edge of the base match. On the other hand, by making the shape of the circle in this embodiment, a white color with a higher reflectance is arranged as an outline in the outer area of the anti-aircraft marker 10, making it easier to recognize points with different reflectance.

When conventional anti-aircraft signs are square-shaped, if the point cloud on the anti-aircraft sign is missing, it is not easy to identify the center from its shape. On the other hand, in this embodiment, even if half or more of the point cloud on the anti-aircraft sign 10 is missing, if at least a portion of the arc that forms the outer periphery of the base 11 can be identified, the center of the anti-aircraft sign 10 can be derived from its shape.

Next, using Figures 7 to 10, we will explain and compare the detection method of the center point (reference point) of the anti-aircraft sign relative to the point cloud between the anti-aircraft sign of this embodiment and the anti-aircraft sign of the comparative example. In each of Figures 7 to 10, the point cloud is represented by multiple points that form a black rectangular shape (■).

Figure 7A is an example of a point cloud for an anti-aircraft sign according to an embodiment, and Figure 7B is an explanatory diagram of center detection in the point cloud of Figure 7A. Figure 8A is an example of a point cloud for an anti-aircraft sign according to a comparative example, and Figure 8B is an explanatory diagram of center detection in the point cloud of Figure 8A. The anti-aircraft sign 50 according to the comparative example (see Figure 8B) is formed in a square shape (a diamond shape with all four corners at equal angles). In Figures 7A, 7B, 8A, and 8B, the point clouds on the anti-aircraft signs 10, 50 have no or almost no missing points.

In this state, when detecting the center point with the anti-aircraft sign 10 of the embodiment, as shown in FIG. 7B, a circular pattern Pa corresponding to the external shape of the anti-aircraft sign 10 is moved in a direction parallel to the paper surface of FIG. 7B relative to the point cloud, and the outer periphery of the point cloud and pattern Pa are aligned. Then, the center position of the aligned pattern Pa is detected as the center position of the anti-aircraft sign 10.

When detecting the center point with the anti-aircraft sign 50 of the comparative example, as shown in FIG. 8B, a square pattern Pb corresponding to the external shape of the anti-aircraft sign 50 is moved relative to the point cloud, and the outer periphery of the point cloud is aligned with the pattern Pb. At this time, it is necessary not only to move the pattern Pb in a direction parallel to the paper surface of FIG. 8B, but also to move it in a direction rotating around an axis perpendicular to the paper surface.

Figure 9A is another example of a point cloud for an anti-aircraft marker in the embodiment, and Figure 9B is another example of a point cloud for an anti-aircraft marker in the comparative example. In Figures 9A and 9B, compared to Figures 7A and 8A, there is a loss of approximately 50% of the point cloud on the anti-aircraft markers 10 and 50.

When a certain degree of loss occurs in the point cloud as shown in Figures 9A and 9B, in the comparative example of Figure 9B, it becomes difficult to set the orientation of pattern Pb in the direction of rotation around an axis perpendicular to the paper surface of the figure. Specifically, the burden of rotating and adjusting the orientation of such pattern Pb within a certain angle range is incurred (see pattern Pb in the two-dot chain line in Figure 9B), which makes it difficult to derive the center point of the anti-aircraft sign 50. In contrast, in the embodiment of Figure 9A, it is sufficient to align pattern Pa with the outer periphery of the point cloud so that all of the point cloud is located inside, and it is possible to omit the orientation adjustment in the rotation direction as in the comparative example. As a result, it is easier to derive the center position with less effort with the circular anti-aircraft sign 10 in the embodiment than with the square anti-aircraft sign 50 in the comparative example.

Figure 10 is yet another example of a point cloud for an anti-aircraft marker in a comparative example. In Figure 10, the point cloud on the square-shaped anti-aircraft marker 50 is in a state where approximately 75% of the point cloud is missing.

As shown in FIG. 10, depending on how the point cloud is lost, the orientation of the pattern Pb in the rotational direction can be applied over a wide range of angles, and this increases the burden of adjusting the movement in a direction parallel to the paper surface of the figure, making it more difficult to derive the center point of the anti-aircraft sign 50. In this regard, the embodiment can reduce the burden by omitting the orientation adjustment in the rotational direction as in the comparative example.

Although the invention disclosed herein has been described in detail above, it is clear to those skilled in the art that the invention disclosed herein is not limited to the embodiments described herein. The invention disclosed herein can be implemented in modified and altered forms without departing from the spirit and scope of the invention as defined by the claims. Therefore, the description in this specification is intended as an illustrative example and does not impose any limiting meaning on the invention disclosed herein.

For example, the reference pattern 12 may be represented using the X-shape of FIG. 6 as shown in FIG. 3A and FIG. 3B. FIG. 3A and FIG. 3B are plan views of an anti-aircraft sign according to a modified example. In the modified example of FIG. 3A, the X-shaped reference pattern 12 is represented by two right-angled isosceles triangles 12b that are colored darkly, such as black. The right-angled corner of each right-angled isosceles triangle 12b is located at the center of the base 11, and the other two corners are located on or near the outer periphery of the base 11. With respect to one right-angled isosceles triangle 12b, the other right-angled isosceles triangle 12b is arranged point-symmetrically with respect to the center of the base 11.

In the modified example of FIG. 3B, the reference pattern 12 of the modified example of FIG. 3A is made smaller in a similar shape, and the 45° corners of each isosceles right triangle 12b are located inward and away from the outer periphery of the base 11. As in FIG. 3B, the reference pattern 12 may be located away from the outer periphery of the base 11.

The reference pattern 12 may also be represented by two ginkgo leaf shapes 12c, as shown in FIG. 4. The ginkgo leaf shape 12c is formed by changing the side connecting the 45° corners of the right-angled isosceles triangle 12b in FIG. 3B into an arc parallel to the outer edge of the base 11.

The leg member 15 is not limited to the configuration of the above embodiment, and various modifications are possible. For example, three or more axial legs may be attached to the underside 11c of the base 11 via a hinge structure, and the legs may be arranged diagonally downward from the underside 11c of the base 11, so that the base 11 is positioned at a predetermined height.

The external shape of the base 11 is not limited to a perfect circle, and may be formed, for example, as shown in FIG. 5, with both radial sides of the perfect circle cut out in a direction perpendicular to the radial direction. As with the above embodiment, the external shape of the base 11 of the present invention may be at least partially formed in an arc shape, so long as the center of the anti-aircraft sign 10 can be identified. It is preferable that the center position of the virtual circle that follows the trajectory of such an arc is the center position of the anti-aircraft sign 10. Note that the concept of an arc shape includes not only shapes that follow the trajectory of a perfect circle, but also shapes that follow various smoothly curving curves such as an ellipse.

The reference pattern 12 may be modified from the shape shown in FIG. 1 as shown in FIG. 11A and FIG. 11B. FIG. 11A and FIG. 11B are plan views of an anti-aircraft sign relating to a modified example different from the above. The modified example of FIG. 11A and FIG. 11B has a non-forming area 20 of the reference pattern 12 in a predetermined area of the surface of the base 11 on which the reference pattern 12 is displayed, i.e., the top surface 11a. The non-forming area 20 is a circular area centered on the center position of the anti-aircraft sign 10, where the reference pattern 12 is not formed so that it is removed. Therefore, the non-forming area 20 is the same color as the top surface 11a of the base 11, that is, white, or a light color similar to white.

In the above embodiment, the reference pattern 12 is two squares 12a (see FIG. 1), but in the modified example shown in FIG. 11A and FIG. 11B, the corner of the square 12a facing the center of the base 11 is formed by a pattern forming portion 21 cut into a quadrant arc shape. The two pattern forming portions 21 are arranged symmetrically with respect to the center of the base 11.

The diameter of the non-forming region 20 in the modified example in FIG. 11A is approximately 11% of the diameter of the base 11, and the diameter of the non-forming region 20 in the modified example in FIG. 11B is approximately 17% of the diameter of the base 11. Therefore, the non-forming region 20 in FIG. 11B has a diameter that is approximately 1.5 times that of the non-forming region 20 in FIG. 11A.

The amount of error during laser surveying differs between the black parts of the reference pattern 12 and the white parts of the top surface 11a of the base 11, with the amount of error being relatively larger for the black parts than for the white parts. This affects the error calculation (particularly in the vertical direction) of the center position of the anti-aircraft marker 10, which is performed after the center position is identified. In this regard, in the modified example of Figures 11A and 11B, a non-forming area 20 that becomes a white part is formed in the center of the base 11, thereby making it possible to suppress the effect of errors caused by the black parts.

In the modified examples of Figures 11A and 11B, as described above, the outer shape of the anti-aircraft marker 10 is made circular, making it easier to determine the center position, and the circular pattern of the non-forming area 20 can be provided as an aid, making it easier to determine the center position.

When a laser is applied near the outer periphery of the anti-aircraft marker 10, a step is generated on the outer edge of the base 11, and depending on the location of the laser irradiation near the outer edge, there is a possibility of a defect. However, in the modified example in which a non-forming area 20 is formed, the circular shape of the non-forming area 20 is specified, and no step is generated on the outer periphery of the non-forming area 20, so that defects in the laser irradiation are less likely to occur, and detection accuracy can be improved.

An experiment was conducted to detect the center position of the anti-aircraft sign 10 by irradiating a laser under the same conditions for the modified example of FIG. 11A and the modified example of FIG. 11B. In this experiment, the center position was easier to derive for the modified example of FIG. 11B, in which the diameter dimension of the non-formation area 20 is larger. This is because the arc of the non-formation area 20 is larger for the modified example of FIG. 11B, making it easier to distinguish the boundary between the black and white areas. In particular, when the point cloud density becomes thin or there are missing points due to the flight altitude of the UAV being increased, it was easier to derive the center position of the anti-aircraft sign 10 for the modified example of FIG. 11B than for the modified example of FIG. 11A.

Here, the external shape of the non-forming area 20 may be at least partially formed in an arc shape, so long as it includes the center position of the anti-aircraft sign 10 inside and allows the center of the anti-aircraft sign 10 to be identified in the same manner as above. It is preferable that the center position of a virtual circle that follows the trajectory of such an arc is the center position of the anti-aircraft sign 10. Note that the concept of an arc shape includes not only shapes that follow the trajectory of a perfect circle, but also shapes that follow various smoothly curving curves such as an ellipse.

As explained above, it is useful for use in surveying with a laser scanner mounted on a UAV and as an anti-aircraft marker installed at a control point.

10 Anti-aircraft mark 11 Base 12 Reference pattern

Claims (3)

An airborne marker used in surveying using a laser scanner mounted on an unmanned aerial vehicle,
The present invention comprises a base made of a thin body and a reference pattern formed on at least one surface in a thickness direction of the base,
The outer shape of the base is at least partially formed in an arc shape ,
the reference pattern includes a plurality of squares that are point-symmetric with respect to a center of the base;
An anti-aircraft marker, characterized in that each of the multiple rectangles has one of its four corners located at the center of the base and one of its other corners located on or near the outer periphery of the base . An airborne marker used in surveying using a laser scanner mounted on an unmanned aerial vehicle,
The present invention comprises a base made of a thin body and a reference pattern formed on at least one surface in a thickness direction of the base,
The outer shape of the base is at least partially formed in an arc shape ,
the reference pattern includes a plurality of triangles that are point-symmetric with respect to a center of the base,
An anti-aircraft marker characterized in that, in a plurality of said triangles, one of the three corners is located at the center of the base and the other two corners are located on the outer periphery of the base or inwardly away from the outer periphery . An airborne marker used in surveying using a laser scanner mounted on an unmanned aerial vehicle,
The present invention comprises a base made of a thin body and a reference pattern formed on at least one surface in a thickness direction of the base,
The outer shape of the base is at least partially formed in an arc shape ,
the reference pattern has a plurality of shapes that are point-symmetric with respect to a center of the base,
A non-forming area of the reference pattern is formed in a predetermined area including a center position of the anti-aircraft sign on the surface of the base on which the reference pattern is formed,
An anti-aircraft marker, characterized in that the outer shape of the non-forming area is formed in an arc shape at least in part.

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