How to set up the image control point correctly during the uav aerial survey
2018/10/12 Source： Author：TJIRC Reading：Time 【Print this page】
Requirements for drone operations and demonstrations are also growing. During the installation of image control point is a crucial link. This also directly determines the display of uav aerial survey results. Generally, professional uav companies will have special technology, so how to properly set up image control points?
1. Determine the number of image control points according to the aerial survey area
The precision and quantity of image control points directly affect the precision of post-processing of air survey data. Therefore, the layout and selection of image control points should be as standard, strict and accurate as possible.
Usually, the number of control points is different for different airfoils.
Taking compound wing uav as an example, it is assumed that the scale result of flying 1:00 is achieved, and 5 image control points are arranged for 3 square kilometers and 10 image control points for 7-8 square kilometers.
Taking six-rotor uav P560H as an example, the result of flying 1:00 scale is that 0.3 square kilometers is suitable for laying 5 image control points.
2. Set image control points in the field
Before laying the image control points, you should first check the geological and geomorphological conditions of the aerial survey area and prepare the oil spray paint, target board (wood or cardboard).
Image control points should be selected on the ground object points with clear impression. When the guidelines and orientation of puncture points cannot be coordinated, they should be dominated by policies.
Image control point selection
Figure (1) image control point selection diagram of test area
As shown in the figure above: after determining the airspace of aerial photography, the image map and electronic map are used to determine the approximate location and number of image control points. In the figure above, there are five image control points (K1/K5, K3/K7, K4/K8, K2/K6, K9/K10 (namely the results of the test area with four corners and the middle position) to control about 0.3 square kilometers.
Note: in the figure above, for the sake of safety, a backup is made next to each control point, to prevent the point from being unusable due to unclear photos, artificial movement and other reasons, and the internal industry steps cannot be pricked.
In the figure above, there are a/b/c/d points, which are used to check the accuracy of the results. Checkpoints should be made according to the actual situation, not necessarily.
Note that if it is a strip survey area, the spots should be arranged on the left and right side of the strip. The points can be arranged on the "S" route. The distance between the adjacent points on one side depends on GSD and the actual situation.
Spray paint
Figure (2) painting as image control point
As above: general cement road, asphalt road and other village road, you can use oil spray paint to mark "ten" signs, pay attention to "ten" signs must be wide, at least 5cm width, so that interior time can be accurately punctured on the photo.
Note: oily spray paint is better than water-soluble spray paint, water-soluble spray paint is easy to be washed. Take 2-4 photos of different viewpoints each time, it is better to have reference objects, so as to make it convenient for interior processing.
1. Try to make the area as flat and level as possible, and don't choose the slope with height difference.
2. If there is a height difference, for example, on the roof Angle of the building, the aerial photography will take the shadow view of the building, and the coordinates of the downstairs Angle of the building cannot be measured as the image control point.
3. The bearing of the measurement point shall be checked with the personnel in the industry, and the center orientation cannot be measured.
4. Use the existing signs on the ground as far as possible to make image control points, such as zebra crossing, sidewalk and other places that can be clearly seen in aerial photos.
The target board
Figure (3) image control point of target board
As shown in the figure above: the target board is much better than the wooden board made by oneself, and the black and white color makes the interior points more precise.
The uav's target board size is about 60cm x 60cm, and the KT board is the best
Measurement of image control points
In the measurement of image control points, the bubble is centered or fixed with triangular support bar, and the orientation and corresponding point number of the measured image control points are accepted.
Determine and set the corresponding instrument antenna type and antenna height (such as control point elevation is especially important).
Finally, we must first recognize the parameters, projection, coordinate system, center meridian and band.
