Overlap & Flight Pattern
There are many options for photo overlap, and we have tested them all. There is a time and place for each overlap setting, but for the vast majority of projects we recommend an overlap setting of 75/75 with nadir images, in a lawn mower (back and forth) pattern.
More data is not always better
There is a common misconception that the higher the overlap, the better data will be collected. Not only does this increase photo amount, and thus processing time exponentially, it also adds a lot of noise to the data. The more overlap there is, the more erroneous matches the software can make, leading to potentially less accurate data overall.
..but sometimes it is
There are some situations where higher overlap does actually help;
semi dense tree cover
areas between large buildings that need to be captured
these higher overlap settings are not guaranteed to improve the accuracy, but do give it the best shot in these circumstances.
A cross hatch pattern or a “grid” pattern can sometimes be helpful in the same ways higher overlap can be, in semi-dense tree cover, as well as in city scape or developed settings where you need to see between buildings.
Off NAdir/ oblique photos
These are any photos taken from an angle other than straight down. These types of photos are not beneficial for photogrammetry.
overlap with variable altitude
As elevation changes throughout the site, so does overlap. Your drone flies at a set altitude above the elevation that you took off from. You want to make sure your drone flies at least 100’ higher than the highest elevation/ obstacle on the site. If this is not accounted for you can run into overlap issues when flying over the higher elevation points (shown in the illustration below).
If possible, take off from the highest point on your site, and do not exceed 400’ AGL.
Another way to deal with elevation change is to use Map Pilots “terrain awareness” feature.
This feature uses the 2003 SRTM model of the earth to instruct the drone to follow the natural elevation changes in place at the time that that model was taken. This option is a paid add on to the Map Pilot app and is convenient for projects with large elevation changes.