How to determine the scale of aerial photography

The scale of aerial photography is the ratio of the horizontal distance between a line segment L on aerial photography image and the corresponding ground line segment L.

Features:

1, which is the same everywhere in the horizontal photos of flat areas, is different everywhere in the aerial photos of uneven areas due to the influence of photo tilt and ground fluctuation, and usually only represents its average value or approximate value. The ratio of the main distance of aerial camera to the average altitude is often used as the photographic scale.

2. The selection of aerial survey scale depends on the mapping scale, which is roughly equivalent to the mapping scale. After choosing the camera and scale, the flying height can be calculated according to the formula (1). When flying, the plane should fly at a predetermined altitude, and the height difference between camera stations on the same route should not be greater than 40m.

3. In traditional photogrammetry, the course overlap is generally defined as 60%, the minimum is not less than 43%, and the maximum is not more than 74%; Generally speaking, the horizontal overlap is 30%, the minimum is not less than 14%, and the maximum is not more than 40%.

Three manifestations of proportion:

1, number (also called digital scale): scale is expressed by proportion or fraction. For example:1:50,000,000 or1/50,000,000.

2. Line segment (also called scale): Draw a line segment on the map and indicate the actual distance with 1cm on the map.

3. Text type: directly write 1 cm on the map to indicate how many meters of field distance. For example, 1 cm on the map is equivalent to 500 meters, or one in 50,000.

4. When drawing a plan such as a map, it is necessary to reduce (or expand) the actual distance according to a certain proportion, and then draw it on the drawing. At this time, it is necessary to determine the ratio of the distance on the map to the corresponding actual distance. The ratio of the distance on a picture to the actual distance is called the scale of this picture. Unit conversion: centimeters on the map, kilometers on the spot, centimeters for kilometers, and five zeros; Kilometers represent centimeters, and two zeros are added to thousands.