What are the advantages and disadvantages of setting up photo control points before and after flight in aerial photogrammetry?

In aerial photogrammetry, the advantages and disadvantages of image control points before and after flight are as follows:

1. Advantages of arranging photo control points before flight: the layout position and number of control points can be planned in advance, which is conducive to improving the density and uniformity of control points.

2. Control points can be accurately measured and marked before flight to avoid mistakes during flight.

3. Before flying, the ground objects around the control point can be cleaned and trimmed, which is conducive to improving the visibility and stability of the control point.

4. Disadvantages of arranging photo control points before flying: it is necessary to plan and arrange control points in advance, which increases workload and time cost.

5, will be affected by weather, terrain and other factors, resulting in inaccurate and unstable layout of control points.

6. Advantages of arranging photo control points after flight: control points can be arranged according to actual conditions to avoid being affected by weather, terrain and other factors.

7. The number and position of control points can be increased or decreased according to actual needs, thus improving the flexibility and adaptability of control points.

8. Disadvantages of arranging photo control points after flight: it is necessary to arrange control points after flight, which increases the workload and time cost;

9. It will be affected by errors and uncertainties in the flight process, resulting in inaccurate and unstable layout of control points.