When placing them on the ground you should:

1. Use a minimum of 3 GCP’s per site (as recommended by some photogrammetry software), however I try to use 5 per site, for sites up to 10 acres.

2. 1 additional GCP per each extra 5 acres of the site.

3. Spread evenly over the flight area (one in each corner and one in the centre).

4. Note areas of interest and place GCP’s around them 

5. Inside the flight area by at least one flight pass width from the boundary (20Mtrs).

6. Have an un-obstructed view from above.

7. Consider any changes in elevation or complex typography.

8. Where the flight area is spilt into flight areas (due to size, topography etc) then there should be no GCP’s inside of the overlap, between the areas unless they are present during the all flights covering that overlap and unmoved from their original position.