1. Layout of photo control
The layout of photo control points plays a key role in later mapping. First of all, at least 5 Phase control points are required for each post. If the terrain changes greatly and the number of vegetation is complex, the image control points need to be encrypted. If the space is not encrypted or evenly distributed, it will cause warpage, the adjustment data cannot meet the accuracy requirements.
II. Image quality
Factors affecting image quality are divided into weather factors and camera itself factors.
Weather factors are mainly wind and haze. When the wind speed is too large, the distribution error of the image control point should not exceed level 5, and the flight should be stopped. First of all, the wind Assembly causes the flight speed and attitude of the aircraft to change too much, resulting in too much distortion of the photos taken from the air and finally blurred imaging. At the same time, it will accelerate the consumption of aircraft kinetic energy, resulting in shortening the flight time, and eventually it may fail to complete the planned area within a limited time.
The main factors of the camera itself are the pixel and exposure time of the camera. The pixel mainly determines the camera itself. The selection of exposure time is closely related to the weather. When the light conditions are not good, we should try our best to increase the exposure time and take photos at the selected two exposure times respectively. By comparing the ISO values of the camera, the smaller the ISO values, the better the photo quality, therefore, select the exposure time corresponding to the photo with a smaller ISO value.
III. Overlap rate
Overlapping rate is an important guarantee to improve photo connection points, but sometimes in order to save flight time or expand flight area, the overlapping rate will be lowered. If the overlap rate is low, each ground object point will only appear in a small number of aerial films, and the amount of extraction connection points will be very small. The small connection points of photos will naturally lead to rough connection of aircraft photos, finally, the extracted connection point adjustment structure is weak. High overlap rate can avoid the above problems.
IV. Flight altitude
The flight height mainly affects the GSD (the actual size of each pixel) in the flight aerial film. The change of flight height will inevitably affect the phase amplitude of the aerial film. Take Diop SV360 as an example, the relationship between flight altitude and GSD. According to the data, the closer the plane is to the ground, the smaller the GSD value, the higher the accuracy. It is also found that it is also very important to select the appropriate flight height for improving the accuracy in areas with great ground fluctuation.
